Encyclopedia Of Animal Science - Agroterrorism potx

Animal welfare has no agreed upon definition even among the scientists who research the topic.[1]However, there is a consensus that the state of the individual animal is the critical issu

Luther Tweeten

Agricultural, Environmental, and Development Economics, The Ohio State University,

Columbus, Ohio, U.S.A

INTRODUCTION

Agroterrorism is the willful, unlawful threatened or

actual destruction of property or people through the

agricultural and food industry to achieve the

perpetra-tor’s ends, usually political The ultimate target may be

food consumers Agroterrorism (or any other form of

terrorism) is a tool of choice in asymmetric power

situations, where the perpetrator perceives an inability

to achieve ends through conventional political, market,

judicial, or educational channels Terrorist threats and

acts are a form of propaganda designed to achieve a

political end by striking fear in people Among the

many forms of agroterrorism, random killing of

many innocent people is especially effective in striking

widespread fear Because everyone eats every day,

some experts conclude that the agricultural and food

industry is an attractive venue through which the

general population can be terrorized The following

paragraphs outline the threat and means to counter it

UNDERSTANDING AND ADDRESSING

THE AGROTERRORIST THREAT

This section outlines characteristics of agroterrorists,

their possible targets, and means to respond to the threat

The following observations characterize agroterrorism

in the U.S.A

 Among industries, the agriculture and food system

has been the most frequent target of terrorists in

the past decade or longer

 Agroterrorists have been home grown

Approxi-mately 100 acts of agroterrorism have been

committed each year by persons from just two

American organizations, the Animal Liberation

Front (ALF) and the Earth Liberation Front

Radicals from other groups such as People for the

Ethical Treatment of Animals have engaged in

petty acts of terrorism, such as throwing paint on

fur coats The only international agroterrorism

activity in the U.S.A has been by the North

American ALF of Canadian origin The

organiza-tion specializes in releasing animals from their cages

on fur farms Turning thousands of mink loose

from a fur farm to fend for themselves is a disasterfor local animals edible by hungry mink, andeventually leads to the starvation of many of thefreed mink The paradox is that any means such asstark cruelty to animals are justified to attain theends sought by the presumed animal-loving zealots

 Agroterrorism has been directed more at destroyingintellectual and physical property than at killingpeople Standard fare includes bombing of offices,laboratories, and experimental plots engaged indeveloping genetically modified organisms withrecombinant DNA Terrorists have tried to shutdown the use of animals to test medications, surgicaltechniques, and cosmetics before they are used onpeople Terrorists have destroyed buildings andmachines that they believed to be encroaching onthe wilderness They have spiked ‘‘old growth’’ trees

to protect them from logging It is not possible

to dismiss the varied activity of agroterrorists asmere pranks because those who intend only todestroy property and science end up destroyinglives both literally and figuratively A recentexample illustrates the tactics.[1]On May 19, 2005,University of Iowa President David Skortonreported on a November 2004 attack on universityanimal research laboratories by the ALF Morethan 300 rodents were removed, equipment wassmashed, and acid was poured on equipment andpapers, causing $450,000 damage The ALF opera-tives sent e-mails to local and national media listingthe names, home addresses, and spouse’s names offaculty who conducted the animal research Thenames of graduate assistants and lab assistants alsowere listed The purpose was to encourage thepublic to harass the named individuals PresidentSkorton called the ploy ‘‘[B]latant intimidation[that] was also successful, as these individualsare still being harassed and are still concernedabout their own safety as well as their families’.’’Terrorists had created a climate of fear; researchers

‘‘ are still concerned about allowing theirchildren to play in their own yards’’ said Skorton

 The agriculture and food sector comprised as it is ofmillions of acres and animals is readily vulnerable

to attack by domestic or international terrorists.Fail-safe protection is prohibitively expensive

Encyclopedia of Animal Science DOI: 10.1081/E EAS 120041359

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Since the ‘‘9/11’’ devastation wrought by Islamic

radicals, Americans are especially concerned about an

attack on the agriculture and food system by an

interna-tional terrorist group such as al Qaeda bent on killing

hundreds if not thousands of people Is such an attack

likely? On March 20, 2005, the Food System Insider

pub-lished the results of a survey of their readers Some 56%

of respondents said they believed ‘‘ there would be a

serious case of agroterrorism in the United States in

the next three years.’’ As for the likely target of

agroter-rorism, 33.3% said food processors, 16.7% said farms/

ranches, 13.6% said feed yards, 12.1% said the

trans-portation system, 7.6% said food services/restaurants/

cafeterias, and 4.5% said retailing These responses

are not scientific but are consistent with the earlier

con-clusion that the agriculture and food sector is vulnerable

to terrorists, in part because it is difficult indeed to

anticipate the time, place, and method of attack over a

highly dispersed industry

Targets of Opportunity

Al Qaedaseeks the spectacular act to strike fear; does

the agriculture and food sector offer such targets?

Given a lack of examples of actual pathogen

agroter-rorism from history, it is well to examine the cost of

(damage from) selected pathogen outbreaks from

nature Terrorists did not originate these outbreaks,

but the examples could serve as a model for some

future attack

Time and place Pathogen Cost or damagea

Ireland 1848 Potato blight Starved millions

Canada 2002 Mad Cow Disease $2.5 billion (1 cow)

U.S.A 2003 Mad Cow Disease $3 4 billion (1 cow)b

The foregoing data[2,3]indicate that the human andeconomic cost of pathogen infestation can be high

A conscious, planned effort by agroterrorists to spreadfoot and mouth disease or mad cow disease over awide area before it could be detected could causedamage far in excess of the numbers shown above

Responding to the ThreatAgroterrorism by animal rightists, radical environmen-talists, antiglobalists (opposed to multinational firmssuch as McDonalds), and neoluddites (opposed tonew technologies such as bioengineering) has becomecommonplace and will continue.[4]Agroterrorist orga-nizations representing these causes operate throughoutthe U.S.A and Western Europe, but on a decentralizedbasis from individual cells That fragmented structuremakes it more difficult for law enforcement agencies

to apprehend the terrorist ‘‘foot soldiers’’ and theirleaders Such radical groups need to be taken moreseriously than in the past The emergence of al Qaedaand other murderous Islamist terrorist groups adds anew dimension because of their determination to inflictmassive economic and human losses on America Atpresent, the issue is how to respond Here are somesuggestions

 Agroterrorism or any other form of terrorism isabominable, but it is important to recognize thatterrorists sometimes have legitimate grievances.These grievances need to be addressed expeditiouslythrough the political system or other means.Responses could range all the way from endingsome cruel animal treatment practices in the case

of animal rightists to promoting a peacefulsettlement of the Palestinian Israeli conflict in theMiddle East in the case of Islamist jihadists

 Enjoin the propaganda war for the hearts andminds of people Terrorists are recruited and driven

to acts of violence by inflammatory speech (includingliterature) and firebrand leaders ‘‘Education’’should not be left to the radicals Incendiary pro-paganda needs to be countered by strong, objectiveeducational programs reaching the target audience.Leaders in the target audience need to be enlistedwhere possible to provide objective information tofollowers

 That agriculture and the food supply are highlyvulnerable to attack from terrorists is a causefor neither panic nor complacency Our highlydispersed agriculture is not easy to shield fromterrorists but the dispersion also makes it difficult

to kill lots of people Tainted food from one tion is likely to be detected before being consumed

loca-by large numbers of people Pathogens in the water

a A range of cost is included in several instances because of disagree

ment in estimates among the sources The cryptosporidium parasite

outbreak in Milwaukee is included although it may have come from

the feces of deer or other wildlife getting into the city water supply.

The source conceivably could have been farm animals.

supply or nuclear weapons employed in cities would

inflict more casualties Terrorists are more likely to

be American environmentalists, animal rightists, or

neoluddite radicals inflicting economic terror than

sent by al Qaeda to kill people

 One of the best pieces of advice is to be alert

Terrorists ‘‘case’’ targets before acting Report

suspicious behavior to the police Good neighbors

watch out for each other

 Know likely targets Candidates include

Con-centrated Animal Feeding Operations; fur farms;

biotech offices, laboratories (especially those using

animals in research), and experimental plots;

commercial activity ‘‘infringing on nature,’’ and

new machinery likely to displace many workers

 The Animal Identification System currently being

introduced in the U.S.A is useful for traceback of

food pathogens to their source, whether the source

be terrorists or an unsuspecting farmer or rancher

 Secure tools used by agroterrorists It is no more

possible to stop a determined terrorist than a

determined burglar from entering your premises

However, making entrance difficult can discourage

a burglar or agroterrorist One stops terrorists like

one stops burglars, except it is especially important

to keep terrorists away from spray airplanes,

ammonium nitrate fertilizers, poisons, explosives

(dynamite), and petroleum fuels When hiring

workers, it makes sense to learn their background

 Know whom to contact Keep telephone numbers

handy to contact police, firefighters, veterinarians,

medical facilities, and the local extension service

agent The latter provides liaison to crop and

livestock specialists who have the expertise and

tools to diagnose and contain pathogens that might

be spread by agroterrorists

 Enforce laws Domestic as well as foreign terrorists

and the networks supporting them need to be

brought to justice Terrorist cells need to be

infiltrated

Institutional support at the state and federal level is

essential to back up local responses In the case of

live-stock, veterinarians are a critical line of defense Local

veterinarians need help from state and federal animalhealth specialists to be knowledgeable regarding mostlikely diseases, chemical, and biological agents used

by terrorists, equipment and expertise for detectingsuch agents, and responses essential to contain andremediate damage The local agricultural extensionagent will have access to the state plant pathologistswho diagnose and remediate problems with plants,much as the animal specialists handle problems withanimals Some state agency such as the Department

of Agriculture needs to be designated by the stategovernor as the lead agency working with the indivi-duals and groups listed above and the state emergencymanagement agency to plan and coordinate efforts toavoid or respond to agroterrorism

CONCLUSIONSThe food and agricultural sector is vulnerable to attack

by agroterrorists The principal threat is from thedomestic radicals inflicting damage mainly to property

An emerging threat is international jihadist groupsbent on killing large numbers of people The latterprefer concentrations of people characteristic of cities.Eternal vigilance is in order Also in order is to remem-ber that terrorists ultimately have always been losers,even if they have had some short-term success

3 Henderson, J FAQs about Mad Cow Disease andIts Impacts; Center for Study of Rural America,Federal Reserve Bank: Kansas City, December2003

4 Tweeten, L Terrorism, Radicalism, and Populism

in Agriculture; Iowa State Press: Ames, 2003

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Dairy Cattle: Waste Management

Department of Animal Sciences, Iowa State University, Ames, Iowa, U.S.A

Joseph P Harner, III

Department of Biological and Agricultural Engineering, Kansas State University,

Manhattan, Kansas, U.S.A

INTRODUCTION

Commercial dairy operations involve breeding of dairy

animals (cattle herein) to produce milk for human

consumption Operations may have more than two

categories of animals All operations will have lactating

(milk producing) and nonlactating (dry) cows

Replace-ment heifers (bred or unbred females and preweaned

calves that are still consuming milk or milk replacer)

may be housed at the facility or at a separate facility

designed explicitly for the care and rearing of young

ani-mals Additionally, mature bulls used for breeding, or

young bulls not yet used for breeding, may be present

In the U.S dairy industry, the number of cows has

decreased from 11 million to 9 million in the last two

decades The average herd size in the U.S.A., and

especially in California, has increased from 40 to 100

and from 200 to 788 cows, respectively, during the

same time period The number of herds has decreased

from 269,000 to 91,000 herds in the U.S.A The trend

for concentrating animals at a given location is in part

a function of an economically viable production unit,

given the opportunity costs of associated land and

farming enterprises Herds that are smaller in number

can be viable when land is debt free, intensive inputs

are not used, or niche markets are established Larger

herds are necessary when land and facilities are being

paid for, land prices are very high, and intensive

man-agement is needed to maintain or improve neighbor

relations The necessity of environmental stewardship

is greater as herd size increases

MANURE AND WASTE STREAM PRODUCTION

characteristic values are available from the American

Society of Agricultural Engineers Standard D384.2

(partially listed in Table 1) The 2004 revision of thetable provides mean values based on defined dietaryintake parameters as well as regression equations toallow for development of site-specific information thatwould assist in designing a suitable nutrient manage-ment plan

the waste stream can contain bedding (sand, per, rice hulls, sunflower hulls, recycled dry manure,sawdust), parlor generated water associated with udderhygiene, cleaning milking equipment, or flushing;spilled or residual feed; rain runoff; foreign material;and trace amounts of medicinal or sanitary com-pounds Daily milk center wash-water (nonflush system)ranges from 19 38 to >568 L=cow=day, when a flushsystem is used.[1] Recent studies on California dairiesindicated average parlor water use of 319 L=cow=day(
170) with a range from 170 to 746 L=cow=day.Attention to water use is critical to successfully design

newspa-a liquid stornewspa-age contnewspa-ainment

COLLECTIONManure can be collected as a solid from corrals ormixed with bedding, as a semisolid if collected fromfreestall lanes where significant bedding was used, as

a slurry when vacuumed or scraped and little bedding

or feed input exists, and as a liquid when flushed

STORAGEThe method of storage is defined by the form of man-ure Manure storage must be managed to minimizenuisance issues (odor, flies, etc.) Solids can be treated

or stacked Semisolids, slurries, and liquids need to beEncyclopedia of Animal Science DOI: 10.1081/E EAS 120023827

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collected in containers or retention=treatment ponds.

Collection of manure as a slurry versus liquid increases

the nutrient density and reduces the volume of material

important for off-site transportation

Storage structures are not present under the animals

in typical dairy operations in the U.S.A Size of the

storage structure depends on the amount of material

generated in a day, the number of days required for

storage, runoff from the rainy season, capacity to hold

runoff from a 25-yr, 24-hr storm, residual sludge or

material in the structure at the beginning of the storage

period, site specific needs, and an added safety factor

TREATMENT AND UTILIZATION

Numerous companies are venturing into the manure

treatment arena Companies may provide a

proprie-tary technology for use (they maintain ownership)

and they own and are responsible for the end product

Other companies have a turnkey system to treat

manure Some of these are in the development stage

Others have a long (positive or negative) track record

The most detailed list of effectiveness of treatment

Solid liquid separation is practiced to reduce water

content of solids to enable a more efficient export,

remove solids from liquids so that smaller particles will

be present in irrigation systems, or reduce volatile

solids loading to a treatment pond, thereby enabling

greater productivity from the pond Although some

solids are removed by the traditional gravity

separa-tion screens, these screens remove relatively little

nitrogen (N), P, or salts These nutrients are soluble

and predominantly remain in the liquid fraction

Gravity flow settling basins or ponds, or a custom

made, large surface area, weeping wall system removes

more solids compared with traditional screens.[3,4]

Another highly effective method of separation is

keeping solids out of liquids when possible When

compared to other separation techniques, scraping or

vacuuming to collect freestall manure or bedding

material as and when the weather permits, instead of

flushing all manure into liquid storage, may result in

higher annual solids removal

Chemical additives and flocculants have been tried

to improve solid liquid separation and P nutrientremoval Chemicals (Alum, other acids, or poly acryl-amide) have been added to manure to enhance theformation of flocculants This was successful underlaboratory conditions Flocculants have not beensuccessful at farm level because of the costs, additionalresources needed to manage the treatment system, andminimal disincentives when excessive P is applied onthe land A few commercial ventures utilizing floccula-tion or precipitation that is followed by dissolved airflotation (DAF) exist Presently, these technologiesare still in the experimental phase for dairy manure.Enhanced biological P removal (EBPR) as a nutrientremoval technique for dairy manure is being evaluated.[5]Acetic and propionic acids are the preferred energysources for P accumulating organisms and are a criticalfactor in EBPR

Composting can be an effective manure treatment.Benefits of on-farm composting include improved man-ure handling, decreased manure hauling costs, improvedland application ability, stabilized N, decreased weedseed viability, reduced risk of pollution and nuisancecomplaints, and pathogen destruction Drawbacks ofthis type of composting include atmospheric emissions

of gaseous compounds, loss of N, and resource tion (labor, equipment, and land must be dedicated tothis activity to maintain a consistent quality of theproduct) An excellent resource for on-farm composting

utiliza-is available.[6]

A key objective of anaerobic digestion is to collectand degrade organic material (solids) in an anaerobicenvironment and to capture the methane gas and con-vert it to electricity Anaerobic digestion in a controlledenvironment can be beneficial to reduce odor Gasesare formed within a structure (not released to theatmosphere) at a pH near 7, where methane produc-tion should be near optimum and there should beminimal formation of malodorous compounds Gasesformed are collected and they undergo combustion toyield electricity Anaerobic digestion is not an effectivetreatment technology for reducing total N, P, or salts.There are numerous resources available The USEPAmaintains a website for location of vendors, equip-ment, etc (http:==www.epa.gov=agstar=resources.html)

Table 1 Manure production and characteristics from the American Society of Agricultural Engineers Standard D384.2

Category Moisture (%)

Total manure(kg/head/day)

Total solids(kg/head/day)

N(kg/head/day)

P(kg/head/day)

K(kg/head/day)Lactating cow

(40 kg milk=day)

Replacement heifer 440 kg 83 48 3.7 0.12 0.020 N=A

N=a, new data not available.

Ap 909

On-Farm Biogas Production-NRAES-20 is available

from the Northeast Regional Agricultural Engineering

Service, 154 Riley-Robb Hall, Cornell University,

and Lanyon[8]prepared a publication identifying many

important questions to ask and answer prior to

instal-lation of an anaerobic digestion system

Gasification of manure is receiving greater attention

from commercial companies The primary objective is

the destruction of manure without causing air

pollu-tion while yielding energy The remaining ash is of high

quality The end disposition of the ash is yet defined

This type of technology should contain N, P, and salts

in the ash

The primary utilization of manure nutrients is as a

fertilizer or soil amendment Effective utilization of

manure necessitates sampling manures, soils, and crops

for nutrient composition, establishing a nutrient mass

balance for the production and crop areas, and

identi-fying alternative outlets when excessive nutrients are

sequestered at a facility

CONCLUSIONS

Dairy operations have increased and will continue to

increase in size The increased concentration of animals

at facilities will result in a more stringent scrutiny of

regulations and an increased need to manage manure

so as to prevent nuisance and utilize nutrients

appro-priately (protective of surface and ground water and

air resources) Animal housing dictates manure

col-lection and storage to a great extent Treatment=

utilization technologies=methodologies include

mecha-nical, gravity, or chemical separation, composting,

anae-robic digestion, gasification, and land application

The primary disposition of manure nutrients is land

application

REFERENCES

1 United States Department of Agriculture In

Handbook, 1992

2 Humenik, F Manure Treatment Options in stock and Poultry Environmental Stewardship

ser-vice, Iowa state, Amer Available through http:==www.lpes.org

3 Meyer, D.; Harner, J.P., III; Powers, W.; Tooman,

E Manure technologies for today and tomorrow,Proceedings of the Sixth Western Dairy Manage-ment Conference, Mar 12 14, 2003; Kansas stateuniversity: Manhattan; KS, 185 194

4 Meyer, D.; Harner, J.P., III; Tooman, E.E.; Collar,

C Evaluation of weeping wall efficiency of solidliquid separation Appl Eng 2004, 20, 349 354

5 Yanosek, K.A.; Wolfe, M.L.; Love, N.G ment of enhanced biological phosphorus removalfor dairy manure treatment in the animal, agricul-tural and food processing wastes Proceedings ofthe Ninth International Symposium, Raleigh,

Assess-NC, U.S.A., Oct 11 14, 2003; Burns, R., Ed.;ASAE Pub #701P1203, 2003; 212 220

Engineering Service, Cornell University: Ithaca,

NY, 1992; http:==www.nraes.org

Engineering Service, Cornell University: Ithaca,

NY, 1984; http:==www.nraes.org

8 Leggett, J.; Graves, R.E.; Lanyon, L.E AnaerobicDigestion: Biogas Production and Odor Reductionfrom Manure, G-77; Pennsylvania State University:Pennsylvania, U.S.A., 1995; http:==www.age.psu.edu=extension=factsheets=g=G77.pdf

Ap 910

Eggs: Composition and Structure

Richard E Austic

Department of Animal Science, N.Y.S College of Agriculture and Life Sciences,

Cornell University, Ithaca, New York, U.S.A

INTRODUCTION

The avian egg is one of the richest and most balanced

sources of nutrients among all of the foods available to

mankind Its biological function is to support the

development of the embryo from fertilization to the

emergence of the newly hatched chick The structure

of the egg is such that it maintains an aseptic ‘‘milieu’’

for embryonic development It protects the embryo

from physical trauma, allows for the exchange of

respiratory gases between the embryo and the

environ-ment, and provides the embryo with all of the nutrients

that are needed for growth and development Eggs are

generally similar among species of birds, but they can

differ in some aspects of their physical and chemical

composition This article briefly describes the physical

structure, chemical composition, and nutrient content

of the egg of the chicken, Gallus gallus domesticus

EGG STRUCTURE

The physical features of the egg are illustrated in Fig 1

The relative proportions of the parts as reported by

Shenstone[2]are shown in Table 1

Most of these features can be observed by visual

examination of the broken-out egg, but all major

com-partments of the egg also have unique microstructures

that can be seen with the aid of the electron

micro-scope The genetics, age, and diet of the hen, size of

the egg, and environmental factors influence the

relative proportions of albumen and yolk in the newly

laid egg.[3]

Yolk

The yolk is an ovum, a reproductive cell complete with

a cell membrane The cell is so large that it would not

remain as a discrete body if it were not for the vitelline

membrane that surrounds it This membrane is a

bilayered extracellular structure that is secreted by

the ovarian follicle and the oviduct.[2]

The surface of the yolk in the fresh egg appears

uniform except for the presence of the blastodisc

The blastodisc of the unfertilized egg is easily observed

as a small white spot, approximately 2 mm in diameter,

on the surface of the yolk.[4]It is larger, 3 4 mm, in thefertilized egg[2] because the embryo usually hasprogressed to the gastrulation stage by the time ofoviposition The latebra is a small sphere of white yolk

in the center of the yolk extending with a narrow neck

of this unpigmented yolk to the blastodisc The centric rings that are shown in Fig 1 are not visible

con-to the naked eye They have been observed in speciallystained eggs and are believed to represent alternatinglayers of yellow yolk that is deposited during the daywhen the hen is consuming feed and white yolk that

is formed at night when the hen is not eating noid pigments are responsible for the yolk’s yellowcolor.[4]These pigments are present in ingredients such

Carote-as yellow corn, corn gluten meal, and alfalfa meal inpoultry feeds.[5]

Egg yolk is composed of particles that are ded in a liquid phase containing low-density lipopro-teins, livetins, several vitamin-binding proteins, yolktransferrin, and salts.[2,4] The largest particles arespheres of white and yellow yolk that range in diameterfrom 50 to 100 mm These contain inclusions that arenumerous in yellow spheres but limited to one or twoinclusions per white sphere Yolk contains an abun-dance of small particles, known as insoluble yolkglobules, which range in size from less than one toseveral microns in diameter and are enveloped inmultilamellar membranes Yolk also contains granulesthat are about 1 mm in diameter and contain lipovitel-lins, low-density lipoproteins, and phosvitin Phosvitinbinds calcium, magnesium, and trace minerals and hasantioxidant properties About 90% of the iron in yolk

suspen-is bound to thsuspen-is protein.[2,4]

AlbumenAlbumen, or egg white, is the clear fluid surroundingthe yolk Although it might appear quite uniform instructure, it actually contains four compartments: athick gelatinous region (the firm albumen), borderedmedially by the inner thin albumen and surroundedperipherally by outer thin albumen The chalaziferouslayer is the fourth compartment It consists of a thinlayer of mucinous fibers that surround the yolk and

Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019584

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are anchored in the firm albumen in the large and small

ends of the egg These anchoring regions, the chalazae,

hold the yolk in the center of the egg They appear as

whitish appendages to the yolk in the broken-out egg

More than a dozen albumen proteins have been

identified.[2,4] All are sources of amino acids for the

developing chick embryo Many have unique

proper-ties such as inhibiting proteolytic enzymes (e.g.,

ovo-mucoid and ovomucin), causing lysis of gram-positive

bacteria (lysozyme), binding certain B-vitamins

(bio-tin-, thiamin-, and riboflavin-binding proteins), and

binding iron (conalbumen) The gel structure of firm

albumen stems from the presence of at least two

glyco-proteins, alpha- and beta-ovomucin, possibly in

asso-ciation with another protein, lysozyme.[4] Egg whites

gradually become thinner during storage and

even-tually lose their gel structure This may be related to

the gradual loss of carbon dioxide from the egg andthe resulting increase in pH of the egg white

Shell MembranesThe inner and outer shell membranes surround the eggwhite The inner membrane is about one-third thethickness of the outer membrane It separates fromthe outer membrane in the large end of the egg afteroviposition This occurs as the egg cools and itscontents contract after oviposition Air enters throughpores in the large end of the egg to form the air cell,which further increases in size over time owing tothe loss of moisture from the egg The outer shellmembrane contains the sites of mineral crystal for-mation during the process of egg formation ElectronFig 1 The parts of an egg (From Ref.[1].)

Table 1 Proportions and solids contents of egg structuresa

microscopy has revealed that the egg shell is embedded

in the outer shell membrane.[6]

Egg Shell

The egg shell contains about 2 g of calcium and

consists of columns of calcium carbonate crystals that

extend outward from the outer shell membrane An

organic matrix is deposited in the areas of crystal

growth during egg-shell formation The matrix

repre-sents only 2% to 3% of egg shell weight but is believed

to be important in the growth of the crystalline

structure of the egg shell.[4]

Several thousand channels exist from the outer

surface of the egg shell to the shell membranes These

channels, or pores, represent spaces between the

columns of calcium carbonate crystals.[6] They are

more numerous and greater in diameter in the large

end of the egg The outer surface of the mineralized

portion of the egg shell is covered with a proteinaceous

coat, the cuticle The cuticle provides the glossy sheen

that is normally visible on the newly laid unwashed

egg It probably functions to plug the openings of the

pores on the surface of the egg shell to prevent the

entry of microbes into the egg

NUTRIENT CONTENT OF EGGS

The egg is a rich source of nutrients.[7,8]Eggs contain

about 6.5 g of protein (Table 2)

The protein is highly digestible and contains an

excellent balance of amino acids Egg protein has been

used traditionally as a standard protein of high

biolo-gical value, against which proteins from other sources

are measured Yolk and albumen contribute about

40% and 60% to the total protein of the egg The edible

part of the egg contains about 5 g of lipids These are

found almost exclusively in the yolk in the form of

lipoproteins About 70% of the lipid is triglycerideand about 30% is phospholipid.[4]

Phoshatidylcholine(lecithin) and phosphatidylethanolamine (cephalin)account for about three-quarters and one-fifth of thephospholipid fraction, respectively Yolk phospholipidsinclude small quantities of lysolecithin, phosphatidyl-serine, sphingomyelin, and phosphatidylglycerol.[2,4]Eggs contain cholesterol, about 212 mg in a 60 g egg.Small amounts of free glucose are present in theegg, but most of the carbohydrates of the egg exist ascomponents of glycoproteins

Yolk lipids are rich in monounsaturated fatty acids,particularly oleic acid, and contain substantial quantities

of polyunsaturated fatty acids The fatty acid tion of eggs reflects the hen’s feed The typical feed isbased on corn meal, soybean meal, and a small amount

composi-of supplemental animal, vegetable, or animal vegetablefat blend as the sources of fatty acids The polyunsatu-rated fatty acids in these ingredients are predominantly

of the omega-6 series (e.g., linoleic and arachidonicacids) Eggs enriched in fatty acids of the omega-3 series(e.g., linolenic, eicosapentaenoic, docosapentaenoic, anddocosahexaenoic acids) are obtained by the inclusion

of flax seed, canola seed, fish oils, some species of algae, or other ingredients containing high levels of thesefatty acids.[9] Eggs enriched in this manner typicallycontain 400 to 500 mg of fatty acids of omega-3 series.Recent research has demonstrated that eggs can beenriched in other lipid-soluble factors such as lutein,beta-carotene, lycopene, conjugated linoleic acid, andoleic acid.[9,10]

micro-Eggs contain 12 of the 13 vitamins that are required

by man: they lack only vitamin C (ascorbic acid).Chickens, like most birds and mammals, can synthesizethis vitamin from glucose, and therefore it is not neces-sary for it to be present in the egg for the development

of the chick The fat-soluble vitamins (A, D, E, and K)are present only in yolk where they associate with thelipoproteins of yolk The remaining vitamins and 12important minerals are present in both yolk and albu-men,[7,8] although not necessarily equally distributedamong both egg compartments

The US Department of Agriculture[8] reports thecomposition of whole egg, yolk, and albumen based

on a running average of values submitted to theirdatabase Currently, the vitamin content of whole eggs

is as follows (in mg per egg): folate: 0.024, niacin:0.035, pantothenic acid: 0.719, riboflavin: 0.239, thia-mine: 0.035, vitamin B6: 0.071, vitamin B12: 0.00065,vitamin E (alpha-tocopherol): 0.97, and vitamin K:0.0003, and (in IU per egg) vitamin A: 487, and vitaminD: 34.5 The mineral content (in mg per egg) is:calcium: 26, copper: 0.051, iron: 0.92, magnesium: 6,manganese: 0.019, phosphorus: 96, potassium: 67,selenium: 0.0158, sodium: 70, and zinc: 0.56 According

to Naber,[7] the biotin, inositol, and choline contents

Table 2 Proximate analysis and energy content of the egga

Amount per egg

Component

Eggwhite

Eggyolk

Wholeegg

a An egg weighing approximately 57 g with 50 ml edible contents (33 g

of egg white and 17 g of yolk).

(From Ref.[8].)

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of whole egg are 0.0097, 8.19, and 437 mg per egg,

respectively The chloride content is approximately

91 mg per egg

CONCLUSIONS

The egg is composed of structures that serve to protect

and nourish the developing embryo It is a source of all

of the essential nutrients except vitamin C Recent

research has demonstrated that the egg can be enriched

in several nutrients by altering the composition of the

diet of the laying hen

REFERENCES

1 U.S Department of Agriculture (USDA) Egg

Grading Manual; Agriculture Handbook No 75;

Consumer and Marketing Service: Washington,

DC, 1969

2 Shenstone, F.S The gross composition, chemistry,

and physicochemical basis of organization of the

yolk and white In Egg Quality: A Study of the

Hen’s Egg; Carter, T.C., Ed.; Oliver and Boyd:

9 Gonzalez-Esquerra, R.; Leeson, S Alternativesfor enrichment of eggs and chicken meat withomega-3 fatty acids Can J Anim Sci 2001, 81,

295 305

10 Surai, P.F.; Sparks, N.H.C Designer eggs: fromimprovement of egg composition to functionalfood Trends Fd Sci Tech 2001, 12, 7 16

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Farm Animal Welfare: Economic Policies

W Ray Stricklin

Department of Animal and Avian Sciences, University of Maryland,

College Park, Maryland, U.S.A

INTRODUCTION

Animal welfare is intricately related to economics The

various animal production systems (beef, pork,

poul-try, cheese, etc.) compete within and with each other

for the same consumer dollar This tends to keep

pro-duction costs and food prices at a minimum

Technol-ogy has replaced labor and driven systems toward

animal confinement and larger production sizes And

the public is increasingly asking for assurance that

farm animals experience a reasonable quality of life,

especially in Northern European counties Opinions,

both inside the United States and outside, matter

because the world is moving rapidly toward a global

economy

DEFINITIONS

The terms ‘‘animal welfare’’ and ‘‘economics’’ each

have multiple meanings Therefore, definitions are

presented herein for clarity, with no intent they be

adopted universally First, the term ‘‘economic’’ is

inclusive of the monetary aspects of capital investment,

labor, profits, losses, taxes, and trade and also policy,

both written and implied Animal welfare has no

agreed upon definition even among the scientists who

research the topic.[1]However, there is a consensus that

the state of the individual animal is the critical issue,

with general agreement that this includes the subjective

mental state, i.e., animal feelings.[2]

ANIMAL PRODUCTIVITY, PROFIT,

AND ANIMAL WELFARE

Production level (number of eggs, volume of milk, rate

of gain, reproductive rate, etc.) is an economic issue in

that profit and loss is dependent on animal

productiv-ity Unprofitable units go bankrupt However,

devalu-ing animals to nothdevalu-ing more than resources, objects

that are simply a means to earning a profit, is

increas-ingly viewed as not being morally defensible.[1] Some

activists have charged that the lives of food animals

are viewed by their owners as lacking inherent value

and that they instead consider the animals as only ‘‘live

stock.’’ But historically, farm animal owners haveviewed animal life as having worth,[1,3]and the major-ity of the public believes farmers and ranchers careabout their animals.[4]However, the public also viewsthe trend toward fewer farms and tendency toward

animals being treated as simply objects for profit.[4]Animal scientists, especially in earlier years, haveargued that high animal production levels are indica-tive of good welfare At an individual animal level thiscontention has merit In assessing the animal care pro-gram of a farm unit, reviewing the records of calvinginterval, pigs per sow, etc., can identify poor welfare.However, high productivity may have negative effects

can result in a metabolic challenge to the animalsystem as in high egg production causing calciumdepletion of the hen’s bones Also, profit is typically

individual.[2]Because profit is based on group mance, greater profits are not always directly related

perfor-to better welfare for individual animals Because ofthe high capital investment costs for housing and therelatively low monetary value of the animal, as inlaying hens, for example, it is sometimes possible forprofits to increase in association with higher stockingdensities along with increased animal morbidity andmortality.[6]

The term ‘‘animal agriculture’’ is common in usageand implies a homogenous group, when, in fact, there

is not one entity identifiable as animal agriculture.Instead, U.S animal agriculture includes a wide range

of production systems For example, the product ‘‘beef ’’involves cattle across environmental conditions of the 50states Additionally, because ‘‘beef’’ is also meat fromdairy cattle when slaughtered, animals involved in theproduction of beef are also found in a wide range ofhousing conditions The various products of animal agri-culture compete for the same consumer dollar Pork,beef, and poultry (broilers) are highly competitive witheach other Consumption levels of these products percapita increase and decrease in relation to the price atthe supermarket, while the overall level of animal proteinper capita remains relatively constant.[7] Competitionamong the animal industries affects the willingness ofproducers to adopt animal welfare standards becauseEncyclopedia of Animal Science DOI: 10.1081/E EAS 120019595

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of the fear that imposed standards of welfare could

cause a loss in their competitive advantage relative to

the other production systems

LABOR, ANIMAL FARMS, AND FARM FAMILIES

Labor cost is possibly the most important economic

issue relative to animal welfare Farm work of 100 yr

ago was ‘‘stoop labor’’ often done by family members,

share-croppers, tenant farmers, etc.[1]Even today labor

policy treats farm workers differently Lowly paid

workers tend to be less educated and may not always

be informed about proper animal handling and care

For example, cases of blatant animal cruelty at

slaugh-ter have occurred, and while these workers were not

farm workers, agriculture still bears the consequences

and some responsibility

During the past 50 yr there was a radical change in

the amount and type of labor associated with

agricul-ture Primarily, there was a decline in the number of

persons working on farms, especially family laborers

(Fig 1) Approximately two persons of every three

were working on farms at the beginning of the past

century, whereas today only about two persons of

technology, both mechanical and chemical starting at

the end of World War II, was responsible for the

freed many people from hard, monotonous labor, but

there was an increase in animal confinement, with less

‘‘freedom’’ for animals to move about and live outdoors

under natural conditions This dramatic change lies atthe root of much of the modern animal welfare move-

coined the term ‘‘factory farming’’ and arguably wasthe most important book in initiating the modern animalwelfare discussion The primary contention of her bookwas, in fact, that less labor and greater technologyadversely affects the welfare of farm animals

ANIMAL WELFARE LEGISLATION ANDINTERNATIONAL TRADE

On a global basis, the relationship of welfare to mics becomes even more complex This is due largely

econo-to trade but is also influenced by human values ing by world region Northern Europeans considerappropriate animal welfare to be inclusive of naturalconditions, whereas Americans tend to emphasizestress, health, and disease as the most important wel-fare measures At times European and American scien-tists each charge the other with not being ‘‘scientific’’when in fact the debate is based largely on different

values have contributed to differing approaches todealing with animal welfare The European Unionhas adopted welfare laws but the United States hasnot Europeans also express greater concern overgenetically modified organisms than do Americans,including concerns about the possible impact onanimal welfare As the world moves toward a global

Fig 1 Declining numbers of farm workersduring the 20th century (From http:==www.usda.gov=nass=aggraphs=fl typwk.htm.)(View this art in color at www.dekker.com.)

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parts of the world will have increasing importance on

trade negotiations and agreements

To date the World Court has ruled that animal

wel-fare is not a basis for a country to refuse importation

of animal products However, trade negotiations on

the topic continue and countries with animal welfare

standards are likely to push for a world standard on

Organi-zation rules Also, because multinational fast food

chains are pressured to maintain animal welfare

dards across international borders, animal care

stan-dards have been adopted by their suppliers in the

United States

Developed countries in North America and Europe

face the possibility of a major shift toward greater

current labor costs associated with processing and

packaging food Only 21% of the U.S food dollar goes

to the farm,[7]and the biggest added cost, over 38%, is

for labor associated with processing (Fig 2) Today,

grain and soybean products are shipped from the

Americas to Southeast Asia, fed to livestock, and

the food products sold mostly in Hong Kong, Taiwan,

Singapore, and Japan In Asia the number of

produc-tion units are rapidly expanding Lower labor costs for

processing, combined with different environmental

standards, could potentially shift a considerable

amount of animal agriculture production outside the

United States Addressing welfare and environmental

standards within the United States and being a serious

participant in international negotiations are important

to ensuring both appropriate animal treatment and a

sound future for American animal agriculture

ANIMAL AGRICULTURE ANDINEXPENSIVE FOOD

Inexpensive food production is a goal of Americanagriculture, and abundant food, readily available to allmembers of society, has much merit In 2001, Americansspent 10% of their disposable personal income on food.[7]However, striving for even greater efficiency of produc-tion and lower priced food can have negative conse-quences, including adversely affecting animal welfare.Hodges[9]summarized the overall view as follows:

‘‘Agricultural and animal scientists need to embrace anew vision beyond the single minded existing pursuit

of biological efficiency The public in the West is nolonger concerned solely with cheap food Other paramount issues define quality of life, including: healthand safety of foods; nutritional value; traditional,regional, locally produced, and organic foods; animalwelfare; sustainable farming, environment, and ruralresources.’’

Ultimately, animal agriculture should not focus onany single issue such as profit or animal welfare.Instead, the goal should be to maximize the benefits

benefits but also ethical, biological, etc to animals,humans, and the environment.[10]

CONCLUSIONSAnimal welfare is very much influenced by economicsbut should be considered as involving more than

Fig 2 Only 23 cents of the dollar spent onfood goes to the farm and the remainder isassociated with marketing.[7] The cost oflabor is the biggest part of the total foodmarketing bill, accounting for nearly half

of all marketing costs (From http:==www.usda.gov=factbook=2002factbook.pdf.)

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monetary endpoints Decisions about animal welfare

have to do with how humans ‘‘ought to’’ treat animals

Thus, animal welfare is about doing the right thing

Polls clearly indicate that Americans wish to continue

eating animal products However, they also ask for

assurance from a third party that animals are given

‘‘appropriate’’ treatment.[4] In a sense the public is

asking that ownership of animal life experiences be

uncoupled from the ownership of the animal as a food

product Implementing this separation presents some

major challenges for American agriculture However,

failure to seriously address this issue and act

accord-ingly could have significant negative consequences

not only to animal welfare but also the future of

ani-mal agriculture

REFERENCES

1 Mench, J.A., Stricklin, W.R., Eds Proceedings of

an International Conference on Farm Animal

Welfare: Ethical and Technological Perspectives

J Agric Environ Ethics 1993, 6 (suppl 1

and 2)

2 Edwards, S.A Animal welfare issues in animal

pro-duction In Nordic Association of Agricultural

Scientists, 22nd Congress, Turku, Finland, July

4 Salem, D.J., Rowan, A.N., Eds The State ofAnimals; Humane Society Press: Washington,D.C., 2001

5 USDA FASS United States Department ofAgriculture National Agricultural Statistics, 2002(http:==www.usda.gov=nass=aggraphs=fl typwk.htm)

6 Craig, J.V Domestic Animal Behavior: Causesand Implications for Animal Care and Manage-ment; Prentice-Hall Inc.: Englewood Cliffs, NJ,

9 Hodges, J Livestock, ethics, and quality of life

J Anim Sci 2003, 81, 2887 2894

10 Stricklin, W.R Benefits and costs of animal culture In Proceedings of the Scientists Centerfor Animal Welfare Symposium on Science and

Guttman, H.N., Mench, J.A., Simmonds, R.C.,Eds.; Scientists Center for Animal Welfare:Bethesda, MD, 1989; 87 92

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Genetics: Population

Dorian J Garrick

Department of Animal Sciences, Colorado State University,

Fort Collins, Colorado, U.S.A

INTRODUCTION

Strictly speaking, genetics refers to the study of

inheritance Its usual interpretation is based on cell

biology, referring to the transmission of hereditary

factors, such as deoxyribonucleic acid (DNA), or,

more specifically, genes, from parents to offspring

Population genetics is concerned with inheritance

from a population perspective considering gene and

genotypic frequencies.[1,2]

GENE AND GENOTYPIC FREQUENCIES

Gene and genotypic frequencies may reflect

equilib-rium or non-equilibequilib-rium conditions A well known

equilibrium condition with respect to a single locus is

known as Hardy Weinberg equilibrium This always

occurs in the absence of forces that influence gene

fre-quency such as selection, migration, or mutation It has

a counterpart in relation to the concurrent

considera-tion of two or more loci known as linkage equilibrium

Traditionally, interest in population genetics was of

a theoretical nature or was applied to simply inherited

Mendelian characteristics such as the inheritance of

coat color, horns, or blood groups The recent

explo-sion in knowledge relating to individual genes that

has arisen from DNA markers and the discovery of

so-called quantitative trait loci has increased interest

in population genetics

A SINGLE LOCUS

Many loci may be involved in the expression of any

characteristic, but only loci that exhibit

polymorph-isms and therefore contribute to variation in observed

performance are of interest from a population genetics

perspective If a characteristic is determined by a single

locus, it is said to be monogenic Characteristics

influ-enced by a small number of loci are oligogenic and

those determined by genes at a large number of loci

are described as polygenic (infinitesimal) At any such

locus, there must be at least two alleles in order to

produce variation We denote a particular locus with

a capital letter such as A, or an abbreviation to sent the trait or gene function Alleles at a particularlocus might be denoted by the same letter in upper case

repre-or lower case repre-or with various superscripts Frepre-or nience, suppose the A-locus contains two alleles A and

conve-a In diploid organisms, such as animals and birds,individuals carry two alleles at each autosomal locus,one inherited from the sire and another from thedam Individuals can therefore have one of three geno-types, AA, Aa, and aa Two of these, AA and aa, aresaid to be homozygous because the individual can onlyproduce one kind of zygote, carrying either A or a Theother genotype Aa is known as a heterozygote as such

an individual can produce two kinds of zygotes, thosecarrying A and those carrying a From a populationperspective, the interest often is in the frequency ofthese alternate alleles (A vs a) and the frequency ofthe various genotypes (AA, Aa, and aa)

HARDY–WEINBERG EQUILIBRIUMSuppose the frequencies of the A and a alleles are pand q, respectively That is, a fraction, p, of thegametes contain A and the remainder, representing

is at random, the frequency of the three genotypescan be calculated from the independent frequencies

of each gamete A proportion p of the sperm will carry

frequency of AA offspring A similar argument showsthat the frequency of aa is q2and the frequency of Aa

is 2pq These genotype frequencies, in the absence ofmigration, mutation, or selection, represent what isknown as Hardy Weinberg equilibrium At equilib-rium, the frequency of gametes produced by thesegenotypes in the next generation will remain at the ear-lier values of p and q Only migration in or out of thepopulation, mutation of alleles, or selection of parentswill change the allele and genotype frequencies Ofcourse, in small populations, allele and genotypefrequencies can drift each generation due to chancesampling, which is, in a sense, undirected selection.The principle of Hardy Weinberg equilibrium can

be used to determine allele frequencies from genotypicEncyclopedia of Animal Science DOI: 10.1081/E EAS 120041456

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frequencies Suppose a rare recessive condition occurs

in 1 in 10,000 births If the locus is denoted with the

letter R, the affected individuals will be rr Their

fre-quency, q2, is therefore 1/10,000 or 0.0001 The square

root of this is q, which in this case is 0.01 The

frequency of the alternate allele R must therefore be

heterozygous individuals who can pass on a copy of

the recessive r allele without themselves having shown

There are therefore 200 times as many individuals in

the population carrying the gene for the condition as

there are exhibiting the condition

TWO OR MORE LOCI AND LINKAGE

DISEQUILIBRIUM

The presence of another locus, say the B locus,

pro-vides the opportunity to consider pairwise frequency

of various alleles and genotypes In the absence of

migration, mutation, and selection, the A and B alleles

will be in Hardy Weinberg equilibrium In some cases,

the A and B alleles will also be in equilibrium, a

condi-tion known as Mendel’s law of independent

assort-ment For example, if the frequency of the A allele is

p and the frequency of the B allele is m, then there will

be a frequency of pm gametes that carry the A and B

alleles together If the A and B loci are located near

each other on the same chromosome, or if the traits

affected by the A and B loci are subject to selection,

this pairwise equilibrium may not exist and the two

loci will be said to be in linkage disequilibrium For

example, if the a and b alleles were very rare alleles

representing recent mutations or introductions to the

population, it may be that the only gametes that carry

a also carry b An offspring created as the product of

such a gamete would be doubly heterozygous AaBb

In one generation, without further migration or

selec-tion, both the A and B loci would exhibit Hardy

Weinberg equilibrium However, if the A and B loci

were very close together so that a recombination event

between the two loci was very rare, most gametes

produced by the doubly heterozygous individual would

carry the haplotype ab or the haplotype AB The

pairwise disequilibrium may take many generations

to disappear This mechanism provides a basis for

marker-assisted selection

Some loci that influence one trait may have

so-called pleiotropic effects and influence other traits

These effects may be complementary when an allele

is favorable for both traits or it may be that the allele

that is favorable for one trait is unfavorable for

another The effect of such genes creates a correlation

between the genotypes for the traits These genetic

cor-relations may be positive or negative and will influence

the performance of one trait when the other trait issubject to selection They will also influence the rate

at which the traits respond to simultaneous selection,such as with an index

BREEDING VALUESThe phenotypes of individuals represented by geno-types AA, Aa, and aa will be influenced by the mode

of gene action The relative frequency of the three types will be determined by the gene frequencies thatdetermine the fraction of gametes that carry the A orthe alternate a allele One interesting issue from apopulation perspective, is the relative performance of

geno-a number of offspring thgeno-at inherit sgeno-ay the A geno-allele fromone parent, with the other parents being randomrepresentatives of the population The difference inperformance of such offspring from all offspring inthe population represents the average effect of allele

A An average effect can be similarly obtained for allele

a The average effects so obtained will be populationdependent as they vary with gene frequency Theseeffects can then be used to quantify the merit of parti-cular parents having the AA, Aa, or aa genotypes An

AA parent has twice the value of the average effect of

A A heterozygous parent has the average effect of Aand the average effect of a This sum of average effects

of each allele is known as their genetic merit or breedingvalue The same phenomenon can be considered for theinfinitesimal model when many genes are involved inthe expression of a trait, even though the loci, their genefrequencies, and modes of action are not known In thatcontext, the breeding value can be estimated by statisti-cal analysis of animal performance over a number ofgenerations Such breeding values are useful toolsfor selection and are routinely estimated in many live-stock species The estimates have a variety of names(EPD, EBV, PTA) depending upon the species andcountry and are sometimes scaled to assist in inter-pretation of the likely phenotypic performance ofoffspring

Variation in genetic merit can come about fromvariation in the merit of sires, variation in merit ofdams, and variation arising from chance sampling

of various gene combinations Chance samplingcomes about from two processes: first, because chro-mosomes are in pairs but only one member of thepair is passed on to the offspring; second, becausethere is typically crossing over between the pair ofhomologous chromosomes, which produces chromo-somes in offspring that are no longer identical tothose the parent inherited from its sire or its dam.The variation produced by this chance sampling isknown as Mendelian sampling and can be shown inthe infinitesimal model to contribute half of the

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genetic variation in the population, which explains

why offspring of the same sire and dam (such as

lit-termates) can vary considerably in genetic merit

CONCLUSIONS

Population genetics is involved with study of

inheri-tance at the population level Early work focused on

theoretical mathematical aspects associated with the

forces that alter gene frequency Modern work has

the luxury of having much data as a result of

compu-terized record collection and the advent of DNA

technologies that has introduced many new aspects

to studies of population genetics, particularly with

respect to the use of wild populations

ARTICLES OF FURTHER INTERESTGene Action, Types of, p 456 458

Genetics: Mendelian, p 463 465

Genetics: Quantitative Published online only

Quantitative Trait Loci, p 760 762

Selection: Marker Assisted, p 781 783

Selection: Traditional Methods, p 784 786

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Genetics: Quantitative

Dorian J Garrick

Department of Animal Sciences, Colorado State University, Fort Collins, Colorado, U.S.A

INTRODUCTION

Genetics is the study of transmission of hereditary

factors, such as deoxyribonucleic acid (DNA), or,

more specifically, genes, from parents to offspring

These factors can be studied at a number of different

levels including those having molecular, genomic,

population, or statistical viewpoints Quantitative

genetics makes use of statistical procedures to study

the variation that results in particular individuals

exhibiting superior or inferior performance

NUMBER OF GENES

Quantitative genetics relates variation in measured or

observed performance to inheritance by providing

var-ious models to explain observed variations in terms of

hereditary factors These alternative models attempt to

describe possible explanations for observed behavior

The true model is never known, but statistical analyses

can be undertaken to determine if observed variation is

consistent with that predicted by the model The

simplest two models to describe genetic merit or

geno-type range from the single gene (monogenic) model

to the infinitesimal or polygenic model.[1,2] With both

extremes, the genetic factors are assumed to result

from diploid DNA sequences, one half (a haploid)

having been inherited from the sire and the other haploid

from the dam The inheritance of these genes is said to

be Mendelian, even though the characteristic or trait

that they influence may not be of a simple Mendelian

nature In the monogenic model, a single locus is

responsible for observed variation In the infinitesimal

model, the genotype is assumed to be collectively

determined by an infinite number of individual genes,

each having a small almost non-significant influence

oligogenic models representing the effects of a few

genes, or mixed inheritance models including one or

more major genes in addition to residual polygenic

effects

A comprehensive range of traits is important to

animal scientists and producers Many traits such as

weaning weight, which are continuous in nature, allows

the observed performance of animals to be ordered

or ranked The average and the standard deviation of

performance can be calculated, with about two-thirds

of the animals performing at a level within one S.D

of the average Other traits tend to be categorical innature, and such traits may or may not be ordered.Consider equine coat color Some common colors arebay, chestnut, black, buckskin, and palomino Thesecolors represent distinct categories and they cannot

be precisely ordered In contrast, many categoricaltraits such as calving ease or litter size can be ordered

A ewe having twins has a litter size that is intermediatebetween a single and triplets Such an ordered cate-gorical trait is often referred to as a threshold trait

PHENOTYPIC VARIATION AND ITS CAUSESThe amount of variation observed in a quantitative orcontinuous trait can be quantified by calculating thephenotypic variance Since animals in different herds

or years typically exhibit different average levels ofperformance, the phenotypic variance, or its squareroot, the phenotypic standard deviation, is not simplycalculated from observed performance of all animals,but is pooled from estimates of the variation among

same herd in the same year, adjusted for systematicinfluences on performance such as their age orcalving date

A few traits or characteristics such as coat colorprovide direct indication of the likely genotype orgenetic make up of the individual Most traits, particu-larly production traits such as bodyweight, milk pro-duction, fleece weight, litter size, or calving difficultyare strongly influenced by environmental effects inaddition to the influence of genes Accordingly, thephenotype or observed performance is usually consid-ered to result from the combined effects of the geno-type and the environment The environment is rather

a loose term and actually refers to at least two differentkinds of influences The first of these might be referred

to as systematic effects These include all the influences

of the physical environment (such as the climate, agement, and level of nutrition) that is common to acohort or group of individuals Additional systematicenvironmental effects include the influence of sex, age

man-of the individual, age man-of the dam, birth, and rearingranks The second kind of environmental influence isEncyclopedia of Animal Science DOI: 10.1081/E EAS 120019652

Ap 922

probably more correctly referred to as non-genetic or

residual effects These influences contribute to the

superiority or inferiority of the performance of an

individual in comparison to its contemporaries of the

same sex and age in the same herd, but are not passed

on Such influences are sometimes partitioned into

so-called permanent environmental influences that

repeatedly affect performance over the lifetime of an

animal, and temporary environmental influences that

are unique to a particular measurement

The measure of relative importance of genetic and

observed within groups of contemporary animals is

known as heritability Heritability can be formally

cal-culated as the proportion of observed or phenotypic

variation that can be attributed to differences in

geno-types It is a measure of the strength of the relationship

between genotype and phenotype Heritability is an

important determinant of response to selection as it

influences the accuracy with which the underlying

genotypes of animals can be predicted from

observa-tions of their phenotypic performance in relation to

contemporaries

Concepts such as phenotypic variation and

herita-bility apply at the level of the population, rather than

to individuals These concepts exist regardless of

whether the trait is influenced by one, a few, or many

different genes Heritability can be estimated from a

statistical viewpoint by relating the superiority or

inferiority of the performance of parents to the

super-iority or infersuper-iority of the performance of offspring If

a quantitative characteristic was entirely due to genetic

merit with no residual or temporary environmental

influences, then the regression of offspring

perfor-mance on perforperfor-mance of a parent would be one-half,

reflecting the fact that each parent contributes half the

genes to its offspring This would correspond to a

heritability of one A lowly heritable trait would

exhi-bit a much weaker relationship between parent and

offspring performance Many production traits have

heritabilities of 0.2 0.3 whereas reproductive and

survival traits typically have even lower heritabilities,

often near 0.1

Some loci that influence one trait may have

so-called pleiotropic effects and influence other traits

These effects may be complementary if an allele is

favorable for both traits or it may be that an allele

is favorable for one trait and unfavorable for

another trait Both of these instances commonly occur,

particularly for genes that influence variation in

fun-damental pathways that contribute to productive

traits The effect of such genes is to create a

correla-tion between the genotypes for the traits These genetic

correlations may be positive or negative and will

influence the response in performance of one trait

when the other trait is subject to selection Such

correlations will also influence the rate at which bothtraits may respond to simultaneous selection, such asfrom use of an index

GENETIC MERITStatistical procedures can be used to quantify thegenetic merit of individuals from a population view-point, based on their own performance and also onperformances of their relatives Suppose a sire has hun-dreds of daughters that produce, on average, 1000 kgmilk more than their contemporaries Individual super-ior performance may come about from the effects ofgenes or from non-genetic or environmental reasons.However, such effects should average out when manyoffspring are considered and so the conclusion would

be that the sire in question was passing on one or morefavorable genetic factors that were contributing to thesuperiority of his daughters This cumulative influence

on offspring performance is known as a progeny ence or a transmitting ability in the beef and dairyindustries, respectively, in the United States Such sireeffects are estimated from performance data and there-fore may be subject to estimation errors These errorscould result in the assessment of the merit of an animalchanging over time To remind users of these assess-ments that they are predictions, the acronyms EPD(expected progeny difference) and PTA (predictedtransmitting ability) are used The value of the genes

differ-of the parents would be predicted as twice the valueobserved in the offspring, reflecting the fact that off-spring inherit a random sample of half of their parents’genes This estimate of the parental value is known asthe estimated breeding value From a Mendelian ormolecular viewpoint, a breeding value (BV) would bedescribed as the sum of average effects of particularalleles or DNA sequences It is interesting that thesame endpoint can be reached using a statistical basisand taking account of the fraction of the genome thatrelatives share in common to assess these values solelyfrom pedigree and performance records

CONCLUSIONSQuantitative genetics bridges the gap among molecu-lar, Mendelian, and population genetics It encom-

marker-assisted selection that can be used to exploitquantitative trait loci (QTL) The introduction ofDNA-based genetic markers has led to the use of sta-tistical approaches to partition the genetic influence

or BV into a polygenic component resulting from anunknown number of genes with unknown gene action

at unknown locations and a QTL effect representing

Ap 923

the influence of DNA sequences that are physically

located at or near a particular genetic marker These

new developments show that the nature of quantitative

genetics is expanding over time and that quantitative

genetics might more appropriately be referred to as

computational biology

ARTICLES OF FURTHER INTEREST

Genetics: Population Published online only

Quantitative Trait Loci, p 760 762

Selection: Marker Assisted, p 781 783

Selection: Traditional Methods, p 784 786

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Greenhouse Gas Emissions from Animal

Production Systems

Donald E Johnson

Department of Animal Sciences, Colorado State University, Fort Collins, Colorado, U.S.A

Kristen A Johnson

Department of Animal Sciences, Washington State University,

Pullman, Washington, U.S.A

INTRODUCTION

The burning of fossil fuels and allied human activities

of recent centuries result in increasing concentrations

of carbon dioxide (CO2), methane (CH4), and nitrous

oxide (N2O) in the earth’s atmosphere These major

gases and other miscellaneous gases and particles act

like a greenhouse, blocking portions of the long-wave

radiation of sunlight energy back out to space The

amount of blockage, and thus warming, varies with

the gas The warming potential of CH4and N2O are

23 and 296 times stronger than CO2 per kilogram of

gas added to the atmosphere Radiative forcing has

caused a global warming of an estimated 0.6C with

the potential for much more warming and a cacophony

of related climate changes with future greenhouse gas

(GHG) releases over the coming decades as described

by the International Panel on Climate Change.[1]

Globally, the major anthropogenic GHG is CO2

(55%) from fossil-fuel combustion in autos, power

plants, etc with CH4 (from landfills, livestock, rice

fields, etc.) comprising 18% and N2O (from

agri-cultural soils, manure storage and use) 6% of the

warming equivalent In the U.S., the portion arising

from CO2is considerably higher, 85%, although an

estimated 12% is currently being offset by carbon

sequestration through land-use changes and forestry

practices Several other gases contribute to warming

including chlorofluorocarbons, ozone, and aerosols

There are also several natural sources of GHGs

Natural sources include wetlands, termites, oceans, and

leakage of hydrate deposits for CH4, as well as bacterial

reactions in soils and oceans, and atmospheric reactions

as sources of N2O.[2]

CONTRIBUTIONS OF ANIMALS AND THEIR

PRODUCTION SYSTEMS

During the production and processing of crops to

feedstuffs, through animal digestion and metabolism,

and during the handling and disposition of manure, a

portion of each of the C and N elements are converted

to the second and third most important GHGs (CH4and

N2O) Additionally, the production, processing, andhandling of animals, feedstuffs, and manure consumefossil fuel and emit the primary GHG, CO2 An analysis

of whole-system emissions by typical beef and dairy duction systems around the U.S.A (Table 1) indicatesthat each U.S beef cow along with associated replace-ments, stocker, and finishing animals produce5500 kg

pro-of CO2equivalent annually Methane and N2O are theprimary sources, 47% and 42% A dairy cow, along withheifers reared to replace her, will produce from 9000 to11,000 kg CO2 equivalent annually depending on milkproduction per cow and dominance of anaerobic lagoonuse for manure disposal Fossil-fuel CO2emissions are arelatively small portion of GHGs from beef operations,but make a substantial contribution to dairy systememissions

As a relative perspective, animal system emissionscan be compared to other economic sector emissions

in the U.S.A As one example, the beef and dairy sectoremission estimates are 128 and 45 Tg CO2equivalent,[4]while passenger vehicles, cars, and light trucks produce

an estimated 1000 Tg annually by U.S EnvironmentalProtection Agency estimates

Livestock CH4EmissionsThe livestock contribution to the global CH4 budgetresults from emissions from enteric fermentation offeedstuffs and anaerobic manure decomposition.Enteric (gastrointestinal) CH4 results from microbialfermentation of dietary components, primarily carbo-hydrate, to volatile fatty acids, hydrogen, and subse-quently CH4within the gut of the animal Ruminantsare the greatest contributors of enteric CH4 because

of their unique gastro-intestinal structure that motes the fermentation of cellulosic diet components

pro-in the rumpro-inoreticulum and also because of theirlarge world population, body size, and appetites Theseanimals produce 96% of global enteric CH4(Table 2)

Encyclopedia of Animal Science DOI: 10.1081/E EAS 120019662

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Horses, pigs, and most other nonruminants also

produce CH4from hindgut fermentation of feed

resi-dues, but this contribution is small (Table 2) Methane

production by microbes in the gut is a mechanism by

which the ruminal ecosystem disposes of excess

reduc-tive hydrogen enhancing continued metabolism of

dietary substrates by other bacteria Methanogenic

bacteria reside in several niches within the ruminal

microbial community and derive energy as they

produce CH4 There is also an active population of

methanogenic bacteria existing in the ruminant hindgut

The majority of CH4 gas is eructated (belched) or

absorbed through the bloodstream and exhaled.[6]

Question: Are CH4emissions from cattle today, any

greater than that from the vast herds of bison in the

U.S.A during the last century? The anecdotal

accounts of bison populations suggest similar amounts

of CH4to that of cattle in the U.S.A today However,

the bison herds were essentially gone before the start of

the more than doubling of atmospheric CH4during the

last century Also, the global population of cattle/

ruminants[7] approximately parallels the rise in CH4

Thus, domesticated cattle or ruminants worldwide

contributed to, but did not by themselves cause, the

global rise in CH4

The amount of CH4 produced by a ruminant isprimarily dependent on diet dry-matter consumption.The chemical composition of the diet can have markedeffects on consumption and in some cases on the

CH4 yield per unit of diet When the predominantfermented ingredients in the diet are cellulose orhemicellulose, CH4 production is the predominanthydrogen-disposal method With fermentable starch,propionate’s role as a hydrogen sink increases and

CH4 yield decreases In fact, most of the mitigationstrategies available enhance propionate and otherhydrogen sinks When starch is the primary fermentablesubstrate, the CH4 yield can fall dramatically Inter-mediate diets, such as those fed to dairy cows, result inthe greatest amount of CH4produced

Emissions of CH4from manure, particularly in theU.S.A., are more prominently from nonruminantsowing to widespread use of anaerobic lagoons formanure management Emissions from lagoons areboth temperature and wind-speed dependent and arenot only a result of the degradative processes occurringduring the lagoon storage period, but can also arisefrom field surface application of the liquids Compost-ing manure solids reduces CH4emissions, but increases

N2O and ammonia emissions Other agricultural sources

Table 2 Global sources of GHG emissions from livestock

of CH4 include rice fields and biomass burning,

estimated to approximately equal enteric and manure

sources Energy production (coal, oil, and gas) and waste

sectors (e.g., landfills) are estimated to produce CH4

emissions about equal to those from agriculture as do

emissions from natural sources (wetlands, termites,

etc.) Overall CH4entry into the atmosphere is estimated

to total 598 Tg/yr, while CH4 sinks including the

hydroxyl ion and soil oxidation total 576 Tg/yr.[8]

This imbalance has resulted in a greater than twofold

increase in atmospheric concentrations to current

levels of 1750 ppb

Emissions of N2O from Livestock Systems

Livestock systems produce N2O during manure

sto-rage and disposition and crop and pasture fertilization,

and from volatilized and leached nitrogen Nitrous

oxide is formed when microbes in soil or manure

oxidize ammonia or organic sources of N to nitrate

(nitrification) under aerobic conditions or during

reduction of nitrate under anaerobic conditions

(denitrification) The major loses from livestock

man-ure storage or accumulation facilities is from fecal

and urine deposited by grazing animals or in dry-lot

facilities where 2% of N is commonly given off as

N2O-N All nitrogen amendments to soils as

manure-N, synthetic fertilizer-manure-N, legume fixed-manure-N, or N in crop

residues are subject to the same microbial processes

and release N2O Variability in soil conditions lead to

highly variable and episodic processes but average

1.25% of N2O-N emissions Additionally, volatilized

or leached N that eventually returns to soils or bodies

of water adds to N2O emissions Simulations of U.S

dairy operations[9] show these emissions to arise in

approximately equal amounts from manure handling

or disposal and from legume or synthetic-N fertilization

of crops and forages

Carbon Dioxide: Energy/fuel Use in Animal

Production Systems

The third source of GHGs from livestock operations is

CO2from fossil fuel use in feed and fertilizer production,

irrigation, transport, and processing Life-cycle analyses

also require estimation of CO2 from embodied energy

use for equipment and building production Although

these costs will vary widely around the world,

approxi-mately 11% and 26% of the total CO2equivalent from

U.S beef and dairy systems, respectively, is produced

from fuel consumption.[3]

Question: Does CO2exhaled by animals metabolizing

feed nutrients add to the GHG burden? No, metabolic

CO2 has been removed from the atmosphere during

photosynthesis, thus contributing no net increase

CONCLUSIONSAnimal production systems do contribute to GHGemissions; however, the opportunity exists to bothenhance animal production systems and reduce GHGemissions simultaneously

The first principle of consideration when evaluatingmethods to reduce livestock GHG emissions is thatmanagement or mitigation interventions need toexamine effects on the whole of the production system.Many trade-offs occur, e.g., changing manure-handlingsystems can reduce CH4but increase N2O, or foragetreatment to enhance digestibility may require fuelenergy inputs, and offset any advantage The secondprinciple is that options that enhance feed or animalproduction efficiency will usually reduce GHG per unit

of product Emissions of all GHGs are rather closelyrelated to the amount of feedstuff going into the pro-duction system; thus, reduced feed inputs reduceGHG outputs

Livestock systems have potential to increased soil-Cstorage to higher plateau levels partially offsettingemissions for a period of years Intensive grazing prac-tices in eastern U.S locations, for example, stored C inpastures to offset from 12% to 18% of total emissionsfrom beef cattle systems.[10] Silvopastoral productionsystems add another dimension and can offset evenlarger fractions of emissions as indicated by estimatesfor Costa Rican cattle operations.[11]

With the value of CO2 increasing to >EU 20/T,methods to capture, decrease, or offset GHG emissionswill likely become economically important and apotential source of revenue by agricultural industries.Opportunities include adoption of methods to decreaselagoon CH4, production of renewable fuel, implement-ing management to decrease dry-lot N2O, enhancingsoil C-sequestration, etc

REFERENCES

1 IPCC Intergovernmental Panel on ClimateChange, Third assessment report, 2004; (http://www.ipcc.ch/pub.htm)

2 EIA/DOE Emissions of Greenhouse Gases inthe United States in 2003; 2004; (www.eia.doe.gov)

3 Johnson, D.E.; Phetteplace, H.W.; Seidl, A.F.Methane, nitrous oxide and carbon dioxideemissions from ruminant livestock productionsystems 44 52; In Greenhouse Gases and AnimalAgriculture, Proceedings of the 1st InternationalConference on Greenhouse Gases and AnimalAgriculture, Obihiro, Japan, November 7-11,2001; Takahashi, J., Young, B., Eds ElsevierScience (www.elsevier.com), ISBN 0444510125,

372 pp

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4 USDA U.S Agriculture and forestry greenhouse

gas inventory: 1990 2001 Tech Bul 2004,

1907

5 Johnson, D.E.; Ward, G.M.; Ramsey, J.J

Live-stock methane: current emissions and mitigation

potential In Nutrient Management of Food

Animals to Enhance and Protect the Environment;

Kornegay, E.T., Ed.; CRC Press, 1996; 219 234

6 Murray, R.M.; Bryant, A.M.; Leng, R.A

Measurement of methane production in sheep In

Tracer Studies on Non-Protein Nitrogen for

Rumi-nants II; International Atomic Energy Agency:

9 Johnson, D.E.; Phetteplace, H.W.; Seidl, A.F.;Davis, J.G.; Stanton, T.L.; Wailes, W.R.Estimates of gaseous and phosphorus emissionsfrom cattle operations Part I: Dairy Cattle AnimalSci Res Rep Colo State Univ 2003, 45 48

10 Conant, R.T Potential soil carbon sequestration

in overgrazed grassland ecosystems GlobalBiogeochem Cycles 2002, 16 (4), 90/1 90/9

11 Johnson, D.E.; Phetteplace, H.W.; Seidl, A.F.Report to USEPA Silvopastoral livestock green-house gas emissions Colo State Univ Ft Collins,

CO, 2003, 80523

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Growth and Development: Peri-Implantation Embryo

Fuller W Bazer

Department of Animal Science and Center for Animal Biotechnology and Genomics,

Texas A&M University, College Station, Texas, U.S.A

Greg A Johnson

Veterinary Integrative Biosciences and Center for Animal Biotechnology and Genomics,

Texas A&M University, College Station, Texas, U.S.A

Thomas E Spencer

Department of Animal Science and Center for Animal Biotechnology and Genomics,

Texas A&M University, College Station, Texas, U.S.A

INTRODUCTION

Guillomot et al.[1]indicated that the phases of

implan-tation in mammals include: 1) shedding of the zona

pellucida; 2) pre-contact and blastocyst orientation; 3)

apposition; 4) adhesion; and 5) endometrial invasion

In contrast to rodents and humans, true endometrial

invasion does not occur in ruminants for which the

sheep will serve here as the prototypical ruminant.[2–4]

IMPLANTATION (SEE FIG 1)

Shedding of the Zona Pellucida (Phase 1)

Morula (16 32 cells) stage sheep embryos enter the

uterus from the oviduct on day 4 post-mating (day

day 6, and ‘‘hatch’’ from the zona pellucida between

days 8 and 9 Loss of the zona pellucida allows the

trophectoderm to expand and make contact with

the endometrial lumenal epithelium (LE) On day 8,

the spherical blastocyst is 200 mm in diameter with

about 300 cells By day 10, it is 400 900 mm in diameter

and contains3000 cells After day 10, the blastocyst

or conceptus (embryo and associated membranes)

develops into a tubular and then to a filamentous form

Pre-contact and Blastocyst Orientation (Phase 2)

Between days 9 and 14 of pregnancy, there are no

defin-itive cellular contacts between the trophectoderm and

the LE, but sheep conceptuses become positioned and

immobilized in the lumen of the uterus for rapid

elon-gation of the trophectoderm On day 11, the spherical,

then tubular, and finally filamentous conceptus

elon-gates to 25 cm or more by day 17 The primitive streak

in the embryonic disc appears at this stage and somitesappear soon thereafter The conceptus is initially local-ized to the uterine horn ipsilateral to the corpusluteum, but elongates into the contralateral horn onday 17 Elongation of the conceptus is critical forcentral implantation and for production of interferontau (IFN-t), the signal for pregnancy recognition.Pregnancy recognition signals ensure maintenance of

a functional corpus luteum for production of terone, the hormone of pregnancy

proges-Apposition (Phase 3)The trophectoderm is in close association with the LEfollowed by unstable adhesion and then onset of appo-sition accompanied by a reduction of the apical micro-villi covering the trophectoderm between days 13 and

15 in sheep The LE undergoes similar modificationfor closer association with the trophectoderm in somespecies The apposition of the trophectoderm involvesinterdigitation of cytoplasmic projections of the tro-phectoderm and the LE beginning at the inner cellmass and spreads along the filamentous conceptustoward the ends of the trophectoderm Uterine glands

of sheep are also sites of apposition as the derm develops finger-like villi that penetrate into themouths of the uterine glands between days 15 and 18and then disappear by day 20 of pregnancy These villiappear to anchor the peri-attachment conceptus andabsorb secretions of uterine glands These villi are alsopresent in cattle, but not in goats

trophecto-Adhesion (Phase 4)The conceptus trophectoderm is firmly adhered to the

LE on day 16 in caruncular and intercaruncular areas

of the endometrium and adhesion is completed onEncyclopedia of Animal Science DOI: 10.1081/E EAS 120019665

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day 22 of pregnancy in sheep IFN-t gene expression in

mononuclear trophectoderm cells begins for pregnancy

recognition during elongation Trophoblast giant

binucleate cells (BNCs) differentiate from the

mono-nuclear trophoblast by day 16, but only monomono-nuclear

trophoblast cells adhere to endometrial LE The BNCs

produce hormones such as placental lactogen and

pro-gesterone that regulate maternal physiology

Tropho-blast BNCs arise from mononuclear trophectoderm

cells by consecutive nuclear divisions without

cyto-kinesis, migrate through the apical trophectoderm

tight junctions of the chorion, and flatten as they become

apposed to the apical surface of the LE The BNCs

then fuse apically with the LE and form syncytia of

trinucleate cells, thereby assimilating and replacing

the endometrial epithelium Subsequently, the

tri-nucleate cells enlarge by continued BNC migration

and fusion to form syncytial plaques linked by tight

junctions that are limited in sheep to 20 25 nuclei

The syncytial plaques eventually cover the caruncular

surface and aid in the formation of placentomes

Indeed, BNCs migrate and fuse with uterine epithelial

cells or their derivatives throughout pregnancy The

uterine LE persists but is modified to a variable

degree, depending on species, by the migration and

fusion of fetal BNCs with the endometrial LE The

sheep placenta is synepitheliochorial, being neither

entirely syndesmochorial without uterine epithelium,

nor completely epitheliochorial with two apposed cell

layers for which the only anatomical interaction isinterdigitated microvilli as in the pig

UTERINE SECRETIONS AND CONCEPTUSDEVELOPMENT

All mammalian uteri contain endometrial luminal andglandular epithelia that synthesize and secrete ortransport a complex array of enzymes, growth factors,adhesion proteins, hormones, transport proteins,amino acids, ions, and other substances referred to col-lectively as histotroph Evidence from human, primate,and subprimate species indicate an unequivocal rolefor uterine histotroph in conceptus survival, develop-ment, production of pregnancy recognition signals,implantation, and placentation Ewes that lack uterineglands (UGKO ewes) produce insufficient histotrophand are unable to support conceptus development today 14 of gestation.[5] Defects in conceptus survivaland elongation in UGKO ewes are not due to altera-tions in expression of steroid receptors, mucin glyco-protein one, adhesive integrins on the endometrial

LE, or to the responsiveness of the endometrium toIFN-t, the pregnancy recognition signal, but likelyare due to deficiencies in secreted adhesion moleculessuch as osteopontin, galectin-15, and glycosylated celladhesion molecule one, which are secreted by the LEand GE.[3,4,6]

Fig 1 Implantation involves five potential phases that involve increasingly complex interactions between the trophectoderm andthe uterine endometrial epithelium and stroma.[1,10]

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PREGNANCY RECOGNITION SIGNALS

(SEE FIG 2)

Primates

The conceptus trophectoderm secretes chorionic

gonad-otrophin (CG), the luteinizing hormone-like hormone

that acts directly on CL to insure maintenance of its

structure and function for continued secretion of

eight-cell stage of development of human embryos,

but secretion of CG increases during implantation,

trophectoderm outgrowth, and pregnancy recognition

Ruminants

The antiluteolytic signal for pregnancy recognition in

ruminants is IFN-t secreted by the trophectoderm

during the peri-implantation period to abrogate the

luteolytic mechanism by inhibiting transcription of the

estrogen receptor alpha and oxytocin receptor genes.[8,9]

This prevents pulsatile release of luteolytic

prostaglan-din F2-alpha (PGF) by uterine epithelia to protect

corpus luteum function In addition, IFN-t increases

expression of a number of interferon-stimulated genes

including interferon-stimulated gene 15 (ubiquitin

cross-reactive protein), major histocompatibility complex-2,

and galectin-15 that may affect the conceptus

Pigs

Estrogens, produced by pig conceptuses between

days 11 and 12 and then between days 15 and 25 of

gestation, are the antiluteolytic signals for recognition

maternal recognition of pregnancy in pigs is based onthe following evidence: 1) the uterine endometriumsecretes luteolytic PGF; 2) pig conceptuses secreteestrogens which are antiluteolytic; 3) PGF is secretedtoward the uterine vasculature (endocrine) in cyclicgilts to induce luteolysis; and 4) secretion of PGF inpregnant gilts is into the uterine lumen (exocrine)where it is sequestered and metabolized to preventluteolysis The transition from endocrine to exocrinesecretion of PGF between days 10 and 12 of pregnancy

is coincident with initiation of estrogen secretion bypig conceptuses that results in a transient release ofcalcium into the uterine lumen within 12 hr and isfollowed by an increase in endometrial receptors forprolactin

HorsesThe equine conceptus inhibits uterine production ofluteolytic PGF as pregnant mares have little PGF inuterine fluids, low concentrations of PGF in uterinevenous plasma, and no episodic pattern of release ofPGF into peripheral plasma Also, endometrial pro-duction of PGF in response to cervical stimulationand exogenous oxytocin is low or absent in pregnantmares Estrogens secreted between days 8 and 20 ofgestation by equine conceptuses may have a role inpreventing luteolysis, but this has not been established.Further, equine conceptuses secrete several proteins(400, 50, and 65 kDa) between days 12 and 14 ofpregnancy, which may be involved in pregnancyrecognition signaling.[8]

Fig 2 The conceptus trophectoderm secretes signalsfor pregnancy recognition that include estrogens in pigsand interferon tau in ruminants These hormones act onthe uterine endometrium to prevent release of luteolyticprostaglandin F2 alpha so that progesterone secretion

by the ovarian corpus luteum is maintained and theuterine glands secrete histotroph necessary for conceptus development

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The peri-implantation conceptus secretes a pregnancy

recognition signal for establishment of pregnancy and

initiates implantation These two critical events must

be successful if a successful pregnancy is to be

main-tained for birth of a viable offspring

REFERENCES

1 Guillomot, M.; Flechon, J.E.; Leroy, F

Blasto-cyst development and implantation In

Levasseur, M.C., Hunter, R.H.F., Eds.; Elipses:

Paris, 1993; 387 411

2 Bazer, F.W.; First, N.L Pregnancy and

parturi-tion J Anim Sci 1983, 57 (suppl 2), 425 458

3 Burghardt, R.C.; Johnson, G.A.; Jaeger, L.A.;

Ka, H.; Garlow, J.E.; Spencer, T.E.; Bazer, F.W

Integrins and extracellular matrix proteins at the

maternal fetal interface in domestic animals

Cells Tissues Organs 2002, 172, 202 217

4 Spencer, T.E.; Johnson, G.A.; Bazer, F.W.;

insights from the sheep Reproduction 2004,

128, 657 658

5 Gray, C.A.; Burghardt, R.C.; Johnson, G.A.;

Bazer, F.W.; Spencer, T.E Evidence that an

absence of endometrial gland secretions in uterinegland knockout (UGKO) ewes compromisesconceptus survival and elongation Reproduction

2002, 124, 289 300

Burghardt, R.C.; Meeusen, E.N.; Spencer, T.E.Discovery and characterization of an epithelial-specific galectin in the endometrium that formscrystals in trophectoderm Proc Natl Acad Sci.USA 2004, 101, 7982 7987

7 Stouffer, R.L.; Hearn, J.P Endocrinology of thetransition from menstrual cyclicity to establish-ment of pregnancy in primates In Endocrinology

of Pregnancy; Bazer, F.W., Ed.; Humana Press:Totowa, NJ, 1998; 35 58

8 Bazer, F.W.; Ott, T.L.; Spencer, T.E ogy of the transition from recurring estrous cycles

Endocrinol-to establishment of pregnancy in subprimatemammals In Endocrinology of Pregnancy; Bazer,F.W., Ed.; Humana Press: Totowa, NJ, 1998; 1 34

9 Spencer, T.E.; Burghardt, R.C.; Johnson, G.A.;Bazer, F.W Conceptus signals for establishmentand maintenance of pregnancy Ann Reprod.Sci 2004, 82 83, 537 550

10 Guillomot, M.; Flechon, J.-E.; Leroy, F cyst development and implantation In Reproduc-

Levasseur, M.C., Hunter, R.H.F., Eds.; Ellipses:Paris, 1993; 396

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Growth and Development: Pre-Implantation Embryo

Fuller W Bazer

Department of Animal Science and Center for Animal Biotechnology and Genomics,

Texas A&M University, Texas, U.S.A

Greg A Johnson

Veterinary Integrative Biosciences and Center for Animal Biotechnology and Genomics,

Texas A&M University, Texas, U.S.A

Thomas E Spencer

Department of Animal Science and Center for Animal Biotechnology and Genomics,

Texas A&M University, Texas, U.S.A

INTRODUCTION

In most species, ovulated ova are at Metaphase II of

meiosis and remain so until fertilized within the

ovi-duct some 5 30 min after ovulation Within 11 22 hr

after fertilization, meiosis is completed and the female

and male pronuclei, each with its 1N or haploid

com-pliment of chromosomes, fuse to establish the 2N or

diploid status with pairing of maternal and paternal

chromosomes The one-cell fertilized ovum or zygote

then undergoes cleavage to form a two-cell embryo

by about 26 hr after fertilization Ova may be either

meiotically immature or chromosomally abnormal,

which contributes to the 25 40% pre-implantation

embryonic mortality in most mammalian species

EMBRYONIC DEVELOPMENT

Following fertilization, most mRNA encoding proteins

in the zygote is of maternal origin, but as the embryo

advances in development, it becomes less dependent

on maternal mRNA as more mRNA transcripts

repre-senting its own genome are expressed.[1]This maternal

to embryonic transcript transition occurs at the 4-cell

stage in pigs and 8- to 16-cell stage in sheep and

cat-tle.[2] Advancing embryonic development results in

genes being silenced, so that the genome loses

‘‘totipo-tency’’ or its ability to orchestrate development of a

normal individual However, the cloning of the sheep

Dolly taught us that the nuclear genome in adult cells

can be reprogrammed to restore totipotency following

somatic cell nuclear transfer, although less efficiently

than cloning by blastomere nuclear transfer using

8- to 16-cell sheep and cow embryos.[3]

Genome imprinting refers to the requirement for

an embryo to have both maternal and paternal

chromosomes (genomes) to develop normally This isbecause of preferential expression of maternal genes

in the embryonic disc for development of the embryo=fetus, while paternal genes are expressed preferentially

in the trophectoderm for development of a functionalplacenta Imprinted genes include those for insulin-likegrowth factor II from the maternal genome and insulin-like growth factor II receptor from the paternal genome,both of which are essential for the development of anormal conceptus

After fertilization, embryos remain in the oviductand enter the uterus at 48 56 hr in pigs, 72 hr in ewes,

72 96 hr in cows, and 144 hr in mares Unfertilizedequine ova are not transported from the oviduct intothe uterus, perhaps because of the lack of production

of prostaglandin E2 However, unfertilized ova ofsheep, pigs, and cows are transported into the uterus.Embryos of most species fail to develop beyond theearly blastocyst stage if confined to the oviduct owing

to the absence of critical factors needed for ment or the presence of embryotoxic factors

develop-The early cleavage stages of mouse embryonicdevelopment require expression of many genes includ-ing 1) phosphoproteins known as cyclins that regulatecell division; 2) heat shock proteins for genome activa-tion during the maternal mRNA to embryonic mRNAtransition; 3) lamins A and B for formation of thenuclear membrane after pronuclei fuse; 4) lamininswhich are extracellular matrix proteins that promotecell adhesion; 5) uvomorulin for compaction and tightjunction formation for blastomeres of morulae tobecome polarized, and form a hollow center, the blas-tocoel, into which water and nutrients are pumped;6) gap junctions for cell cell communication; and7) sodium-potassium ATPase for active transport ofwater, electrolytes, and essential nutrients.[3]Blastocystformation is a key stage in early embryonic develop-ment when cells segregate into the embryonic disc,

Encyclopedia of Animal Science DOI: 10.1081/E EAS 120041186

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trophectoderm, extraembryonic endoderm, and

blasto-coel necessary for continued development and

differen-tiation to a conceptus [embryo and associated

extraembryonic membranes (Fig 1)]

Beginning at the two-cell stage of embryonic

development, many growth factors are expressed that

influence cellular proliferation and differentiation

including transforming growth factor-a and -b,

insu-lin-like growth factor-I and -II, fibroblast growth

factor-7, epidermal growth factor, and insulin

Proto-ncogenes and viral-like genes incorporated into the

embryonic genome are also expressed and include

c-mos that regulates meiosis, c-fos that is a

trans-cription factor, c-erb that encodes epidermal growth

factor receptor, c-fms that encodes colony stimulating

factor-1 receptor, and oct-4 that encodes for germ line

differentiation.[2]

As pre-implantation embryos develop, increased

carbon dioxide production reflects changes in

meta-bolic activity, and there is increased uptake of

precur-sors for RNA (uridine), proteins (amino acids), and

glycoproteins (glucosamine) as well as water and

glucose for general metabolism

BLASTOCYST DEVELOPMENT AFTERHATCHING FROM ZONA PELLUCIDA[1]

Before blastocysts develop into a conceptus, they

‘‘hatch’’ from the zona pellucida The trophectodermexpresses plasminogen activator that converts plasmi-nogen to plasmin which is a protease that degradesthe zona pellucida to allow the blastocyst to emergeand continue development in cows (Day 9), mares(Day 8), ewes (Day 7), pigs (Days 6 7), mice (Day 4),and humans (Days 7 8)

Pig embryos are 0.5 1-mm diameter spheres whenthey ‘‘hatch’’ from the zona pellucida, increase in size

by Day 10 of pregnancy (2 6 mm), and undergo amorphological transition to large spheres (10 15-mmdiameter) and then tubular (15 mm  50 mm) andfilamentous (l mm  100 200 mm) forms on Day 11.During the transition from tubular to filamentousforms, pig conceptuses elongate at 30 45 mm=hrremodeling of trophectoderm However, hyperplasia

of trophectoderm is responsible for subsequent growthand elongation of pig conceptuses to 800 1000-mmlength by Day 15 of pregnancy Rapid elongation of

Fig 1 Embryonic development during the pre implantation period begins with the zygote and continues with early cleavagestage embryos, and blastocysts which transition from spherical to tubular and filamentous forms The polar bodies (extrudedextra sets of chromosomes following meiosis and fertilization), blastomeres, zona pellucida, inner cell mass or embryonic disc,trophectoderm, and blastocoel are illustrated

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