Black''''s veterinary dictionary 21st edition - I pot

TheBovine Animals Records, Identification andMovement Order 1995, as amended by theCattle Identification Amendment Regulations 1999 and the Cattle Identification of OlderAnimals Regulati

Iatrogenic Disease

Any illness resulting from treatment, such as

the side-effects of some drugs Adverse drug

reactions were suspected in 130 of 39,541 cases

treated at the Veterinary Hospital, University

of California, Davis In 66 cases there was

reasonable evidence to link the reaction

observed to the drug Antibiotics and

antipara-siticides were incriminated 21 times, with

ana-phylaxis being the most commonly observed

reaction There were 3 deaths following the

administration of procaine penicillin

(inadver-tently intravenously) to a lamb; potassium

penicillin (10,000 units/kg) to a cat; and

oxyte-tracycline (25 mg/kg) to a cow Anaesthetic and

related agents were involved 20 times Severe

clonic convulsions developed in 5 cats receiving

more than 80 mg ketamine hydrochloride;

cardiac arrest, hypotension, dyspnoea and

muscular rigidity in 2 horses given xylazine

(1 mg/kg intravenously); and severe

bradycar-dia and respiratory arrest in 2 dogs given

fentanyl-droperidol Anti-cancer drugs were

implicated in 10 cases with the most dramatic

reactions being observed in 5 dogs treated with

5-fluorouracil One of these died as a result of

neural toxicosis (See also SIDE-EFFECTS;DRUG

INTERACTIONS.)

IBK

Infectious bovine keratitis (infectious ophthalmia

of cattle) (See EYE,DISEASES OF.)

IBR

Infectious bovine rhinotracheitis (See

RHINO-TRACHEITIS.)

Ibuprofen

A non-steroidal anti-inflammatory drug, much

used in human medicine It has a narrow

margin of safety in dogs, in which it can cause

a sometimes fatal gastric ulceration The same is

true of flurbiprofen

Ice, Ice Cubes

Of use in cases of haemorrhage from the

stom-ach, as an aid to control bleeding from wounds,

and as an application in cases of meningitis and

paraphimosis; also in cases of hyperthermia and

animal-to read the data in the chips

A database of animals so identified is kept,under the name Anibase, by Animalcare Ltd.,

of Common Road, Dunnington, York YO1SRU (see also MICROCHIP)

Identification of Cattle

This is controlled by law in the UK TheBovine Animals (Records, Identification andMovement) Order 1995, as amended by theCattle Identification (Amendment) Regulations

1999 and the Cattle (Identification of OlderAnimals) Regulations 2000, requires that allcattle be identified by an ear tag in each ear.Each animal must have a ‘passport’ that mustaccompany it wherever it goes and in whichthe following details must be entered: date ofmovement on to a particular holding, or date

of birth on the holding; eartag number; breed;sex; dam’s identification number (replacementear tag where applicable) When the animal ismoved off a holding, its age or date of birth, theholding from which it is moved, and that towhich it is moved are recorded Ear tags must beapplied to dairy cattle within 36 hours of birthand, in other cattle, within 30 days of birth

Identification of Goats

Identification of Goats is controlled by theSheep and Goats (Records, Identification

I

and Movement) Order 1996, as amended.

Requirements are essentially the same as for

sheep (see below) except that plastic ear tags are

not recommended as goats will chew them

Identification of Horses

Under the Horse Passports Order 1997, as

amended, each horse must have a passport

prepared as specified The document must be in

French and English Details of the individual

horse are given and a silhouette of the animal

is filled in with the markings Information of

vaccinations and dates of administration must

also be stated in the passport There is also

pro-vision for the results of veterinary examinations

to be included and signed by the veterinary

surgeon in charge of an event in which the

horse is entered, or when the animal is about to

undertake a journey

Identification of Pigs

All pigs must be identifiable to the pemises of

origin, under regulations set out in the Pigs

(Records, Identification and Movement) Order

1995 Breeding stock are usually ear-tagged

before leaving the breeding farm Pigs for

slaughter are usually identified by a slap mark;

those travelling across an EU frontier must be

ear-tagged Records must be kept of pigs born

on a holding Very strict measures have been

taken to control disease transmission, because

many viruses multiply rapidly in an infected

pig and the quantity of virus shed can be much

more than is the case with cattle, sheep or

goats with the same infection All movements

of pigs must be recorded in a specified manner

Regulations set out the format for the

declara-tion of pigs moved off a holding, moved from

a farm for breeding, exhibition, artificial

insem-ination or veterinary treatment, and returned

to the farm after having left it for breeding

pur-poses The form of declaration is also specified

for the movement off a farm of pigs that have

been fed waste food (NB feeding of catering

waste, including swill, is banned), and for those

moved from a collection centre to a farm Pigs

must not be moved to an abattoir within 72

hours of their arrival on a holding; normally,

pigs can only be moved after at least 20 days

Identification of Sheep

Identification of Sheep is controlled by the

Sheep and Goats (Records, Identification and

Movement) Order 1996 (as amended) Sheep

moving into the EU and sheep leaving Britain

must be identifiable by ear tag Animals must

be marked before they are moved off the

holding where they were born

IgA, IgE, IgG and IgM

IgA, IgE, IgG and IgM are antibody/immunoglobulins found in the blood serumand also in secretions from mucous membranes.(See IMMUNOGLOBULINS;SECRETORY IgA.)

4 months old It has been suggested that there

is a hereditary predisposition to this condition,which often affects the whole litter In manyinstances, the trouble is recognised only atthe bacon factory, having caused no apparentillness in the pigs Those that die, on the otherhand, do so from perforating ulcers and peri-tonitis, after showing evidence of thirst, a bluishcolour of the skin, and collapse (See PORCINE INTESTINAL ADENOMATOSIS.)

Ilium is another name for the haunch-bone, the

outer angle of which forms the ‘point of the hip’

The ilium is the largest and most anteriorly

situated bone of the pelvis (See BONE.)

Imbalance

A term used to describe, for example, a faulty

calcium to phosphorus ratio in the food of an

animal, or an excess of one hormone in the

bloodstream, or a deficiency of another – with

resulting disease (See RICKETS; INFERTILITY;

METABOLIC PROFILES;CALCIUM SUPPLEMENTS;

DOGS’ DIET.)

Imidocarb Dipropionate

A drug used for the treatment and prevention

of bovine babesiosis (Redwater fever, Babesia

divergens infection) It is given, by subcutaneous

injection in the neck, at the first clinical

appear-ance of the disease; all animals in the same

group should be treated as a precaution Some

animals may have an anaphylactic reaction that

could be fatal Imidocarb has also been used for

treatment of canine babesiosis, although it is

not registered in the UK for this purpose In the

dog it is given by slow intravenous injection or

intramuscularly at a dose of 5 to 6 mg per kg

bodyweight, repeated after 2 to 3 weeks

Immobilon/Revivon (Large

Animal)

(Novartis) is a neuroleptanalgesic, i.e combines

sedation with analgesia It combines etorphine

hydrochloride with acepromazine Given by

intravenous injection in the horse, it provides

immobilisation and analgesia useful for restraint

and minor surgical procedures Immobilon

does not, like morphine, cause excitement,

vomiting or defecation It does, however, act as

a respiratory depressant, and slows heart action

Immobilon is reversible in its effects by means

of Revivon (diprenorphine hydrochloride) It

is absolutely essential that the manufacturer’s

directions are followed

Precautions Immobilon is rapidly fatal for

man and must be used with great care A

veterinary surgeon died within 15 minutes after

accidental self-inoculation when a colt made a

sudden violent movement Unfortunately the

antidote, Narcan (naloxone), was not available

Donkeys are more sensitive to Immobilon

than are horses and it is not licensed for

that species If used, about half the dose

recommended in the horse is adequate

Recommended precautions include the

wearing of gloves to avoid skin contamination

(which has required hospital treatment), andprotection of the eyes Once the dose has beenwithdrawn from the container into the syringe,the needle should be discarded and a freshone inserted into the injection site; the syringecontaining Immobilon is then attached to theneedle and the dose injected An assistant capable of administering the antidote mustalways be on hand

Immune-Mediated Disease

Immune-Mediated Disease include GUS; FELINE INFECTIOUS PERITONITIS; MYAS- THENIA GRAVIS THROMBOCYTOPENIA and

PEMPHI-POLYARTHRITISmay also, in some instances, beimmune-mediated diseases (See AUTO-IMMUNE DISEASE.)

Lymphocytes play an important part in theimmune response, attacking cells containingthe antigens This happens in graft rejectionand organ transplants, in reaction to malignanttumours, and in infections where bacteria,viruses or other parasites are present insidehost cells

B lymphocytes are the precursors of the

plas-ma cells which secrete antibodies B cells haveantibody-like receptors on their surfaces whichaid in the recognition of specific antigens (See under BLOOD; B CELLS; T CELLS; RETICULO- ENDOTHELIAL; ANTIBODIES; IMMUNOGLOBU- LINS;SECRETORY IgA.)

360 Immunisation

I

an antiserum or antitoxin (See IMMUNITY;

VACCINES;ANTISERUM.)

Side-effects Immunisation is not always

attained without side-effects (See SERUM

SICK-NESS;ANAPHYLACTIC SHOCK.) In human

medi-cine both serum shock and serum neuritis may

occasionally follow the use of equine antitetanus

serum or of antitoxin made from this

Immunity

Immunity is the power to resist infection or the

action of certain poisons This immunity is

(1) inherited; (2) acquired naturally; or (3)

acquired artificially

Natural immunityThere are some species

of animals that are not affected by diseases or by

poisons that are dangerous to others The

snake-killing mongoose of India possesses an

immunity against cobra venom; the pigeon can

withstand large doses of morphine without

harm; fowls are resistant to tetanus; the horse

does not become affected with foot-and-mouth

disease; rats are not attacked by tuberculosis;

the ox is immune from glanders; man is not

affected by swine fever and many other diseases

that are fatal to the lower animals, while, with

the exception of the monkey, animals are not

susceptible to syphilis It is probable that species

immunity cannot be broken down even by

massive inoculation of the causal agent

A degree of immunity to locally occurring

infections is transmitted to it by the medium

of the colostrum in its mother’s milk (See

COLOSTRUM;IMMUNOGLOBULINS.)

Acquired immunityresults from an attack

of some disease from which the animal has

recovered It is probable that most diseases

confer a certain amount of immunity, but this

varies greatly It may be life-long, or virtually

so, as in sheep pox, swine fever or erysipelas;

in most instances, however, its duration is less,

and in some only temporary For example,

cat-tle may be attacked by foot-and-mouth disease

several times during their lives, and horses

after recovery from one attack of tetanus may

have a second natural attack The immunity

conferred by recovery is liable in many of the

viral diseases (e.g blue-tongue), and in some

protozoal diseases to break down in the

pres-ence of massive infection subsequently

Recovery from a disease involves a process of

natural immunisation against that disease, the

toxins or other antigens present in the body

being destroyed by antibodies elaborated by

the body tissues

Artificially acquired immunity is of 2varieties, either active or passive

(a) Active immunity may be artificially duced by inoculating an animal with a vaccine(i.e dead or attenuated bacteria or virus) orwith a toxoid

pro-(b) Passive immunity is that form of artificialimmunity obtained by injecting into the body

of 1 animal, blood serum drawn from the body

of another animal which has previously beenrendered actively immune by injecting particu-lar antigens The serum contains antibodies

or ‘antitoxins’, which enable an in-contactanimal to resist an infection, or enable analready infected animal to overcome the infec-tion, so that an attack of illness – if it occurs

at all – is milder than it would otherwisehave been (See ANTISERUM.) A young animalmay acquire passive immunity through thecolostrum of its dam which had beenimmunised with this purpose in mind (For anexample, see LAMB DYSENTERY.)

The immune system normally ‘learns’ to criminate between self and non-self antigensearly in development, leading to the normalstate known as self-tolerance A newbornmouse or rat injected with large numbers ofcells from a genetically foreign individual willgrow up tolerant of the foreign allo-antigens

dis-of the donor, so that, for example, it will accept

a skin graft from the donor which would normally be rejected It has been shown thatthis induced state of ‘neonatal tolerance’ ismaintained by suppressor T-cells

There are many complexities involved inimmunity, which is far from being the simplesubject it may here appear (See IMMUNE RESPONSE;ORIFICES.)

Immunodeficiency

This may involve a specific factor, such as body or lymphocytes; or a non-specific factorsuch as a complement component In eithercase the deficiency results in some failure ofthe IMMUNE RESPONSE, so that viral, bacterial

anti-or fungal disease may ensue

Deficiencies of immunity can be either mary, due to congenital dysfunction of theimmune mechanism, or secondary

pri-Primary immunodeficiency has beenstudied more fully in humans than in animals,although a condition of foals called ‘inheritedcombined immunodeficiency in foals ofArabian breeding’ has been documented inAmerica

Theoretically, if the deficiency is mainly ofB-lymphocytes, the animal is likely to have

Immunodeficiency 361

I

measurably low levels of immunoglobulins and

a deficiency of lymphoid follicles in lymph

nodes Such an animal would be susceptible

to pyogenic bacterial infection, but would be

able to cope with most viral infections

Conversely, if the deficiency is mainly of

T-lymphocytes, the animal will have reduced

‘delayed skin hypersensitivity’ and will be more

susceptible to viruses

Foals affected by the inherited combined

immunodeficiency frequently suffer from

adenoviral pneumonia due to their inability

to resist infection

Secondary partial immunodeficiency

is much more common, and is being

increas-ingly recognised as an important cause of failure

to recover completely from certain diseases

Severe malnutrition, certain viral infections,

exposure to X-rays, and corticosteroid therapy

can all lead to a reduction in the immune

response (See also IMMUNOSUPPRESSION.)

Immunofluorescent Microscopy

This is a useful laboratory method of diagnosis,

described as specific and very sensitive It

enables a virus to be identified during the

course of an unknown infection It can

demon-strate the presence of swine fever virus, for

example, even before the appearance of

symp-toms Results can be obtained within a matter

of hours

The principle involved is that antigens in

tissues are identified by using their ability to

respond to, and fix, the homologous antibody

previously labelled with a fluorescent tracer

which does not affect its properties

The method has demonstrated swine fever

virus using impressions from lymph nodes

taken from pigs killed during the first 60 hours

after experimental infection The virus is

revealed first in the cytoplasm as a diffuse

granular fluorescence; later bright, fluorescent

particles become visible within the nucleus

The term ‘fluorescent antibody test’ is

applied to this technique (See also under RABIES.)

Immunoglobulins

Immunoglobulins – found in blood, colostrum,

and most secretions – are proteins produced

by PLASMA CELLSin response to stimulation by

antigens, and play an important part in the

IMMUNE RESPONSE Immunoglobulins

inacti-vate or destroy antigens In cattle, 4 main

classes of immunoglobulin are recognised: IgA,

IgE, IgG, and IgM

IgA is mainly secreted locally in mammals Its

function is aimed at combating micro-organisms

entering the body at a specific site, e.g upperrespiratory tract, lungs, intestines

IgE is present in increased amounts inanimals with allergies It is attached to themast cells and, on exposure to the antigen,anaphylactic and allergic mediators are released.IgG is the main circulating immunoglobulinand the one responsible for transferring passiveimmunity from parent to offspring

IgM is found in the serum and is the 1st body produced in an immune response It isthe only antibody produced by fish

anti-All domestic animals have IgA, IgG andIgM; a 5th immunoglobulin, IgD of uncertainfunction, is found in some other species,including man

ANERGY;LEVAMISOLE;SPLEEN.)The occurrence of anergy following certainviral infections is worth emphasising; affectedanimals show a reduced cell-mediated response,especially following infections by viruseshaving a cytotoxic effect on lymphoid cells, e.g.Newcastle disease virus

Immunosuppressantsinclude TEROIDS and cytotoxic drugs such as

in its socket that the eruption of the nent tooth below is prevented, this is known asdental impaction Impaction of rumen or ofcolon means that food materials have becometightly packed into these organs, causing ablockage (See STOMACH, DISEASES OF;

perma-INTESTINES,DISEASES OF; and COLICin horses.)

and abdomen in puppies It is characterised by

the formation of painless pustules, shallow,

thin-walled, and usually projecting upwards

above the level of the surface of the skin It

is seen in puppies affected with worms,

distem-per, and teething troubles, in bitches and

cows after parturition, and in other animals

(See also ACNE.)

Implantation

This term is used in connection with the

appli-cation beneath the skin of pellets containing

medication released gradually to provide a

long-lasting effect Microchips coded with

identity data are also implanted (See

HOR-MONES IN MEAT PRODUCTION;CAPONISATION;

also IDENTICHIP.)

Implant

Any material, tissue, or object inserted into

the body on a more or less permanent

basis Implants may be prosthetic, such as

replacement hip-joints; biodegradable, such as

long-acting medicinal preparations; or for the

purposes of identification, such as electronic

microchips

Importing/Exporting Animals

Many animal-owners – including sophisticated

travellers completely familiar with passports,

visas, and vaccination certificates – overlook

the fact that they cannot legally take their

pet animals with them across any and every

national frontier Some governments exercise

a total ban on the import of certain species

of animal; others require prior vaccination

and production of a certificate; others insist

upon an animal going straight into quarantine

on arrival Australia and New Zealand, for

example, will admit dogs only from each other’s

territories or from the UK

Pet animalsDogs and cats may travel to and

from certain countries and the UK, without the

need for quarantine, provided that strict

condi-tions for vaccination against rabies and health

checks are observed For details, see under PET

TRAVEL SCHEME

The Export of Animals (Protection) Order

1981 laid down certain welfare requirements

for the export of cattle, sheep, goats, and pigs

from Britain

There are restrictions on the import of cattle

and semen on account of BLUE-TONGUE and

other diseases

Sheep Animals imported to Britain from

outside the EU require a period of month-long

on-farm isolation following release from thereception/quarantine station During the isola-

tion period, testing for maedi/visna, Brucella

ovis, and Mycoplasma agalactiae is carried out;

with slaughter or re-export required for positivereactors

(See also HORSES,IMPORT CONTROL; BIRDS,

IMPORT CONTROL;RABIES;QUARANTINE.)

Impotence

Inability of the male to mate successfully.Causes include malformation of the genitalorgans, weakness, starvation, and constric-tions resulting from injuries or operations.Impotence may be only a temporary phase inthe life of the animal from which it recov-ers with rest and good food (See also PENIS;

INFERTILITY.)

Imprinting

This is a mental process in which an inborntendency in the animal causes it to attachitself to a set group of objects or a singleobject within a few hours after birth It is

a very important process if the younglamb or calf is to be properly suckled andcared for

Inbreeding

Mating of closely related animals It may bepractised deliberately to preserve desirable char-acteristics, but tends to encourage undesirableand enfeebling ones

Incidence

In relation to disease outbreaks, incidencedescribes the number of new cases in aparticular area in a specific time period (see also PREVALENCE)

There are no upper incisor teeth in domesticated

ruminants (See TEETH.)

Inclusion Bodies

Round, oval, or irregular-shaped structures of a

homogeneous or granular nature, found in cells

during the course of viral infections, e.g Negri

bodies in nerve cells in rabies; Bollinger bodies

in epithelial cells in fowl pox

Inclusion Body Hepatitis

A viral disease of chickens, and also of

inten-sively reared pheasant poults In broilers the

disease may appear at about 5 to 7 weeks of

age, giving rise to an increased mortality but

with some birds remaining healthy

Incompetence

Inability to function effectively The term is,

applied e.g to the valves of the heart when, as

a result of disease in the valves or alterations in

the size of the chambers of the heart, the valves

are unable to close the orifices which they

should protect (See HEART DISEASES.)

Incontinence

Inability to control faecal and urinary function

Incontinence may follow injury to the spinal

cord (See PARALYSIS.) Faecal incontinence alone

in the dog and cat may result from DIARRHOEA,

STRESS, or possibly weakness of the sphincter

ani in old animals

Urinary incontinence may be associated with

a dog with an enlarged prostate gland relieving

bladder pressure indoors (See also under DIABETES

INSIPIDUS.) Old dogs may be unable to avoid

incontinence at night, owing to kidney lesions

A rare cause is an ectopic URETER

Occasionally urinary incontinence is a sequel

to spaying of the bitch, and is attributed either

to a hormonal effect or to adhesion between the

vaginal stump and the bladder or urethra

In the cat, as in the dog, chronic nephritis

in the elderly animal is a common cause The

animal is obliged to drink more, and to pass

urine during the night-time Stress may be a

factor too; for example, the appearance of an

aggressive entire tom cat in the neighbourhood,

being left alone for long periods, or the

addi-tion of a baby or another cat to the household

(See also POLYDIPSIA.)

Incoordination

Incoordination is a term meaning irregularity in

movement Various muscles or, in some

instances, portions of 1 muscle contract or fail to

contract without relation to each other or to the

whole Deliberate purposive movements are nolonger possible or are carried out imperfectly

bovine 14 days at earliestPiroplasmosis, other forms Up to 3 weeksPleuro-pneumonia,

contagious bovine 3 weeks to 3 monthsPleuro-pneumonia,

contagious equine 3 to 10 daysRabies 10 days to 5* monthsRinderpest 4 to 5 daysAfrican horse-sickness 6 to 8 daysStrangles 3 to 8 daysSurra 5 to 30 daysSwine fever 5 to 15 daysTetanus, horse 4 days to 3 weeksTetanus, ox 5 to 8 daysTexas fever 6 weeksTuberculosis 2 weeks to 6 months(*but see under RABIES )

Caution It is always wise to allow at least aweek more than the longest incubation periodgiven before allowing an animal that hasbeen in contact with an infection and has notdeveloped the disease to resume its placewith other healthy animals (See also INFECTION;

ISOLATION;QUARANTINE.)

Indicator

A substance used in chemistry, etc., to show by

a colour change that a reaction has taken place.Litmus is an example (See also COMPLEMENT.)

disease from one animal to another Exposure

to infection may or may not be followed by

dis-ease, depending upon whether the potential

host animal has or has not a useful degree of

immunity against that particular infective

agent, whether the animal is well nourished,

not under stress, and has not any other major

infection, disease, or defect which might lower

its power to resist the new infection (See

IMMUNOSUPPRESSION;IMMUNODEFICIENCY.)

The virulence or otherwise of the infective

agent, and the quantity of it, will also have a

bearing upon whether disease will follow For

example, a heifer vaccinated against Brucella

abortus will normally be able to resist exposure

to these organisms; but her immunity might

break down if challenged by a massive dose of

B abortus.

With rabies, for example, there is a

‘thresh-old’ dose of virus, and below this the infected

animal will not become rabid (at any rate in the

absence of stress)

Susceptibility to infection is also influenced

by genetics For example, see K88 and MAREK’S

DISEASE

Concurrent infectionsThe average farm

animal is host to several different parasites at

one and the same time – including viruses,

mycoplasmas, bacteria, fungi, and worms

Accordingly, when one speaks of a calf having

pneumonia, it is unrealistic to imagine that,

say, the parainfluenza 3 virus (causing the

inflammation of the lungs) is the calf ’s sole

resident parasite

Some parasites may be present in relatively

small numbers and not be causing active

disease Some, owing to the host’s powers of

resistance (the immune response), may be on

the decline Others may have a sudden

oppor-tunity for multiplication and increased activity

as the host’s resistance becomes lowered by

some additional infection or by stress arising

from cold, insufficiency of good food, poor

ventilation, or the rigours of transport, etc

Again, infections should be thought of as

not merely mixed but changing all the time,

developing, and with complex interactions

between a number of factors, including

man-agement ones (See under RESPIRATORY DISEASE

IN PIGS.)

In respiratory diseases there is often a

syner-gism between viruses and certain bacteria In

canine distemper, for instance, Bordetella

bron-chiseptica is quick to invade in the wake of the

canine distemper virus and produce bronchitis

Foot-rot in sheep is often a mixed bacterial

infection, with Fusiformis necrophorus causing

sufficient damage to permit the entry of

Bacteroides nodosus Liver-flukes and bacteria

may both be involved in production of BLACK DISEASE

Experimental work at the Institute forResearch on Animal Diseases, Compton, hasshown that fluke-free cattle can withstand anintravenous dose of 108 Salmonella dublin,

whereas those infested with live-fluke are killed

by this same dose

Clinical and subclinical infections

Exposure to infection may lead to overt orclinical disease in which symptoms are inevidence; or there may be a subclinical infection

in which few if any symptoms – detectablewithout laboratory aids – are shown A goodexample is subclinical mastitis (See MASTITIS

IN THE COW.)Infection may persist in an animal which hasrecovered from a disease and is no longer show-ing symptoms but is excreting the infectiveagent Such an animal is known as a carrier.For example, a bull may be a carrier of brucel-losis; a dog of leptospirosis; a horse of equineinfectious anaemia; a cat of feline leukaemia

Routes/modes of infection An animalmay breathe in air containing droplets in whichthe infective agent is present, e.g influenzavirus or tubercle bacillus This is sometimescalled an aerosol infection

The oral route provides a common mode ofinfection Infective material may be licked, aninfected carcase eaten, or a cow may eat feedcontaminated with salmonella organisms oranthrax spores (In some instances, an infectiveagent, such as salmonella, is already in theintestine but becomes pathogenic when itsbacterial competitors are mostly destroyed by

an antibiotic See DIARRHOEA– Horses.)Spirochaetes and hookworm larvae areexamples of parasites which can enter the hostthrough unbroken skin Small, even insignifi-cant, wounds can be followed by tetanus Bitingflies can transmit diseases (see under FLIES), andticks are notorious vectors Dog bites and catscratches can lead to rabies, the virus of whichcan penetrate intact mucous membrane

Infection may be transmitted at mating, e.g.brucellosis by the carrier bull Dourine in thehorse, and venereal tumours in the dog, are 2other examples of infections transmitted atcoitus Congenital infections also occur

Inter-species infections Many organisms have a wide range of possible hosts,e.g the rabies virus, the influenza viruses, the

micro-Infection 365

I

anthrax bacillus Infections from man to farm

animals are ANTHROPONOSES Farmers may

also be interested in diseases which arise in one

species following their use of buildings which

previously housed another species For

exam-ple, turkeys have become infected in this way

with swine erysipelas, which also affects game

birds (See also under HOUSING OF ANIMALS.)

With cattle kept in association with pigs (as in

North America), acute interstitial pneumonia

may occur in cattle due to the pig worm Ascaris

suum (See also DOG KENNELS.)

Infections transmissible from animals

to man are listed under ZOONOSES In

Britain, those of importance to farmers and

stockmen include brucellosis, Q-fever, canicola

fever, Weil’s disease (leptospiral jaundice),

loup-ing-ill, anthrax, erysipelas, tuberculosis and

salmonellosis

Blood cells which counter infection

When bacteria gain entrance through a wound

in the skin, for example, they are attacked by

white blood cells (leucocytes) The first to

attack are neutrophils, which have their origin

in the bone marrow They pass through the

walls of the capillaries and engulf the bacteria

Monocytes perform a similar task when

they have turned into macrophages, but in

addition to engulfing bacteria they also dispose

of disintegrating neutrophils Lymphocytes

(T-cells or B-cells) also reach the site of

infection (See LYMPHOCYTES; also INTERFERON,

IRON-BINDING.)

Other aspects of infection are dealt with

under separate headings such as ANTIBODY;

COLOSTRUM; FOMITES; IMMUNE RESPONSE;

IMMUNITY; ISOLATION; NOTIFIABLE DISEASES;

SignsBreathing difficulties which may be

evi-dent only when the birds are at rest A reduced

egg yield Misshapen eggs may be laid; this may

persist following recovery Mortality is usually

low and due to secondary infections such as

mycoplasma or E coli.

Prevention Live vaccines are available tocontrol the disease; compound vaccines offerprotection against other avian viral diseases aswell as infectious bronchitis

Infectious Bursal Disease (IBD)

Infectious bursal disease (IBD) of chickensaffects the Bursa of Fabricius, an important part

of the avian immune system, leaving the birdswith lowered resistance to infection It is alsoknown as Gumboro disease from the town

in Maryland, USA, where it was first fied Young birds between 1 and 5 weeks areaffected, with a peak at 31⁄2 weeks Mortalityfrom IBD may be high; because of subsequentinfections, high rates of mortality will continue.The main signs of disease are listlessness anddiarrhoea Post-mortem examination showshaemorrhage or a caseous plug in the bursa.Prevention is by vaccination of breeding stock

identi-Infectious Canine Hepatitis

(see CANINE VIRAL HEPATITIS)

Infectious Coryza of Chickens

Infectious coryza of chickens is caused by

Haemophilus paragallinarum The disease is

sudden in onset and spreads so rapidly that it

366 Infectious Bovine Keratoconjunctivitis

I

Infectious bronchitis can result in a marked oration in egg quality with consequent heavy eco- nomic loss The illustration shows some of the effects, which include roughening and scoring of the shell Shells may also be distorted and thin, or soft-shelled eggs may be laid by infected birds.

deteri-seems as if all the birds have been infected

simultaneously Clinical signs include swelling

of the head, wattles and sinuses, discharges

from the eyes and nose, coughing, noisy

breath-ing, lack of appetite and depression Mortality

is low but recovery takes time

Infectious Haematopoietic

Necrosis

A viral disease of salmonid fish, at present

confined to North America and Japan

Infectious Laryngotracheitis

(see under AVIAN)

Infectious Nasal Granulomata

in Cattle

In certain parts of India, cattle in restricted

areas (sometimes in single herds only) may

become affected with this condition Large

tumour-like masses develop in connection with

the frontal sinus and the turbinated bones in

the nasal passages

The cause is a schistosome, Schistosoma

nasalis, which is present in the veins of the nasal

mucous membrane

Treatment Injections of various antimonial

preparations have been used, but they have

toxic side-effects Praziquantel is among other

drugs that may be effective, but regular

admin-istration is required Prevention by control of

the intermediate snail hosts is preferable

Infectious Necrotic Hepatitis

(see BLACK DISEASE)

Infectious Pancreatic Necrosis

A viral condition of salmonids that is a

NOTIFI-ABLE DISEASEthroughout the EU The clinical

disease lasts only about 4 days Affected fish

often swim on their sides or with slow spiral

movements and sink to the bottom of the

pond They may be darker than normal in

colour and have swollen abdomens It is

mainly, but not exclusively, a disease of young

fish Losses are around 20 per cent but the

survivors do not thrive There is no treatment

Infectious Salmon Anaemia

A NOTIFIABLE DISEASEof viral origin Infected

salmon are pale and lack energy They may try

to gulp air to make up for a lack of oxygen in

the blood There is no treatment; affected pools

or cages of fish are slaughtered and any eggs,

etc destroyed under the provision of the

Animal By-products Order 1999 for high-risk

material

Infectious Pustular Vulvovaginitis

A reproductive disorder caused by infectiousbovine rhinotracheitis (see under RHINOTRA- CHEITIS,INFECTIOUS)

Infectious Tracheobronchitis

(see KENNEL COUGH)

Infective Drug Resistance

Resistant strains of bacteria may arise as a result

of chromosomal mutation More commonly,drug resistance is carried by PLASMIDS (See ANTIBIOTIC RESISTANCE.)

Infertility

Inability of the female or male to reproduce.Insidious but great losses are directly due tofailure to breed on the part of otherwisepromising animals The immediate loss tothe individual owner of livestock is not soapparent as with certain specific diseases, but it

is infinitely greater than the loss accruingfrom any other single specific or non-specificdisease This loss is made up by the keep ofthe barren animals, the absence of offspring,reduction of the milk supply, and interferencewith breeding programmes (See also CALVING INTERVAL.)

Causes The most common and importantcauses of infertility can be grouped forconvenience under the following headings

1 Feeding and ConditionUnder-feeding

is a common cause of infertility in heifers Thediet must include adequate protein of goodquality and sufficient vitamins, especially vita-min A, plus essential trace elements includingcopper and iodine

Excessive fat in cows, heifers or bulls maylead to infertility problems or to inability on

Infertility 367

I

Hypoplasia of the left ovary of a cow of the Swedish Highland breed Compare its size with that of the normal right ovary from the same animal (The ruler is graduated in centimetres.)

the part of the male to accomplish coitus (See

also FATTY LIVER SYNDROME.)

In cows, temporary infertility may

appar-ently be closely associated with the feeding at

about the time of service Cows losing weight

are likely to be affected, especially if fed on

poor-quality hay or silage With ad lib feeding

systems, heifers and more timid cows may

not be receiving enough roughage Kale is

sometimes responsible

In ewes, infertility and fetal death are always

serious in many hill areas, the result – to quote

Dr John Stamp – ‘of keeping pregnant sheep

under conditions of near-starvation during

the winter months when weather conditions

are atrocious’ (See DIET; FLUSHING OF EWES;

STILLBORN PIGS; REPRODUCTION; VITAMINS;

KALE;SELENIUM.)

2 Environment and Management A

sudden change of environment, close

confine-ment in dark quarters (formerly the

lot of many a bull), and lack of exercise may all

predispose to, or produce, infertility Abnormal

segregation of the sexes and the use of

vasec-tomised males (for purposes of detecting

oestrus) are other factors A low level of

nutri-tion may cause a quiescent or dormant state

on the part of the ovaries At the same time

there are seasonal cycles of sexual activity, and

a ‘failure to breed’ during the winter months

may be natural enough, even if the farmer

regards it as infertility This ‘winter infertility’,

as it is often called, may be influenced by

tem-perature, length of daylight, lack of pasture

oestrogens, underfeeding, etc At this season,

heifers often have inactive ovaries, while in

cows irregular and ‘silent’ heats give low

con-ception rates

Infertility may result from the oestrogenic

effects of red clover in the UK, as well as from

subterranean clovers in Australia

In outdoor pig herds, ‘summer infertility’ is

common, partly due to seasonal loss of fertility

in the boars

The most frequent reason for poor fertility is

poor management In cows, poor oestrus

detection or timing, or bad technique if

artificial insemination is used, are common

Similar problems occur in pigs In cattle and,

particularly, pigs, when natural service is

used, all matings must be seen and at least

2 undertaken within the heat period In sheep,

fertility problems often follow when too few

rams are used, or those which are too young

or unproven

3 Diseases of the Genital Organs in the

FemaleWhile there is a very long list of such

diseases, their overall importance in causinginfertility is much less than that of managementproblems such as poor oestrus detection.Inflammation or other disease of the ovaries:ovaritis; the non-maturation of Graafianfollicles, from any cause, and the presence inthe ovary of cysts (which often form from

a corpus luteum), are causes of infertility;another is blocked Fallopian tubes

Persistent corpora lutea: as a true clinicalcondition, these are not very common Wherethey do exist, the animals may have a uterineinfection The persistence of the corpus luteumprevents the ripening of the Graafian follicle,

so the animal does not display oestrus and isnot mated (See under OVARIES, DISEASES OF;

HORMONES;HORMONE THERAPY.)Inflammation of the uterine mucous mem-brane: a large number of cases of infertilitycan be ascribed to infection of the uterus(metritis) or the oviduct by organisms (For alist of the infections which cause infertility,

see under ABORTION For infections causinginfertility in the mare, see under EQUINE GENITAL INFECTIONS.)

When the condition is mild, following a vious calving, it may disappear spontaneously,but in many instances it persists and becomeschronic Associated with inflammation of themucous membrane of the uterus or oviduct isoften a persistent corpus luteum in the ovary.Carelessness during parturition, the use ofunclean instruments or appliances, decomposi-tion of retained membranes, and other similarfactors, also bring about infection of the uterus.Brucellosis though not necessarily itself a cause

pre-of sterility, by lowering the vital resistance pre-of theuterus, favours infection by a multitude of otherorganisms which normally may be non-patho-genic The details of uterine infection, includ-ing salpingitis (inflammation of the oviduct), inthe causation of sterility, are highly technical,but, generally speaking, it may be said that thepresence of organisms in the uterus, or the pres-ence of the products of their activity, either killsthe spermatozoa, or renders the locality unsuit-able for anchorage of thefertilised ovum (orova), with the result thatit perishes

Abnormalities of the cervix may preventconception – mechanically when the lumen isoccluded or plugged by mucus of a thick tena-cious nature; and pathologically when there isacute inflammation of the mucous membrane

of the cervix, or even of the whole uterus.Scirrhous cervix – where much fibrous tissue islaid down in the cervix – when very advancedmay cause sterility, but by itself is not usually

of great importance It is much more serious

368 Infertility

I