coursera week 6 DAIRY PRODUCTION AND MANAGEMENT

Chin Resting: Secondary sign of estrus where a cow will rest her chin on the back of another cow Colostrum: The first milk the cow produces for the calf that is rich in antibodies Conce

AM/PM Rule: Relative to the timing of artificial insemination, cows detected in heat in the

morning should be inseminated in the afternoon and cows detected in heat in the afternoon should be inseminated the following morning

Antibodies: Immunoglobulins that are absorbed by the calf’s stomach and that provide

immunity to during the first weeks of a calf’s life

Bulbourethral gland: Accessory sex gland that contributes to the production of seminal plasma Cervix: Cartilaginous tube connecting the uterus to the vagina.

Chin Resting: Secondary sign of estrus where a cow will rest her chin on the back of another

cow

Colostrum: The first milk the cow produces for the calf that is rich in antibodies

Conception Rate: The number of pregnant cows divided by the number of cows inseminated Corpus Luteum: Structure formed at the site of ovulation that produces progesterone.

Diestrus: Longest period of the estrous cycle from day 5 to day 18 characterized by high

circulating concentrations of progesterone

Endometrium: Component of the uterine wall that produces secretions (uterine milk) to nourish

the embryo and will form the maternal side of the placenta

Epididymis: Thin tube connected to each testis that matures and stores sperm prior to

ejaculation

Estrogen: Steroid hormone produced by the follicle that causes the cow to exhibit signs of

estrus

Estrous Cycle: Time between two periods of estrus, which averages 21 days in dairy cattle but

can range from 18 to 24 days

Estrus: Stage of the estrous cycle when the cow will stand when mounted by other animals

Defines day 0 of the estrous cycle

Follicle: Structure on the ovary that produces estrogen and the oocyte.

Heat Detection Rate: The number of cows detected in heat divided by the number of cows

eligible to be detected in heat during a 21 day period

Heat Detection Rate: The number of cows detected in heat divided by the number of cows

eligible to be detected in heat during a 21 day period

Interferon tau: Protein hormone produced by the embryo that maintains CL function

Interservice Interval: The interval between inseminations in a cow that fails to conceive.

Libido: Male sex drive or willingness to engage in copulation

Metestrus: Period from the end of estrus until progesterone concentrations in the blood increase.

Nutritional status: A measure of whether feed intake is adequate to support the physiologic

demands of the animal (growth and production)

Oocyte: Female gamete or egg that will fuse with the sperm and form the embryo

Ovary: Female gonad that houses and matures oocytes and forms the corpus luteum.

Oviduct: Thin muscular tube that connects the ovary to the uterus Site of fertilization.

Ovulation: Release of the oocyte from the follicle.

Penis: Male copulatory organ that is the common exit for the reproductive and urinary systems.

Pheromones: Organic acids produced by vaginal bacteria that are detected by the bull and

provide information about the stage of the estrous cycle

Placenta: Organ that forms in the uterus as an association between the developing embryo and

uterus that provides nutrients, oxygen and produces hormones The placenta is shed during parturition

Pregnancy Rate: Primary metric of the success of the reproductive management program that is

calculated by multiplying the farm's heat detection rate (or submission rate) by conception rate

Proestrus: Period from CL regression until the cow enters estrus.

Progesterone: Steroid hormone produced by the corpus luteum that is essential for the

maintenance of pregnancy

Prostaglandin F: Lipid hormone produced by the uterus that regresses the CL and initiates the

onset of proestrus

Prostate: Accessory sex gland that contributes to the production of seminal plasma

Puberty: Age at which a cow can carry a healthy calf to term without compromising her health.

Seminal Vesicles: Accessory sex glands that contribute to the production of seminal plasma Sperm: The male gamete that combines with the oocyte at fertilization.

Submission Rate: The number of cows in ovulation synchronization programs that are

submitted for insemination divided by the number of cows that started the ovulation

synchronization program

Testes: Paired gonads in the bull that produce testosterone and sperm.

Testosterone: The primary male sex steroid produced by the testes and essential for sperm

production and male sex drive

Transition period: Period approximately 3 weeks before and 3 weeks after calving when the

cow is at increased risk of disease and injury

Uterus: Site of fetal development during pregnancy.

Vagina: Common opening of the reproductive and urinary tracts which is the site of semen

deposition during natural mating

Vas deferens (ductus deferens): Long muscular tubes attached to each epididymis that carry

sperm to the base of the penis just prior to ejaculation

Voluntary waiting period: Period between calving and insemination where cows are given time

to recover from calving and adjust to the new lactation

Withers: The highest point of the shoulder.

Hello

My name is Troy Ott, and I'm a professor of Reproductive Biology in

the Department of Animal Science at Penn State

My research focuses on factors affecting fertility in dairy cows, and

I teach reproduction to undergraduate and graduate students

Before we begin to talk about reproduction in a dairy cow,

it is important that we take a moment to look at the big picture

What is it that we want for these beautiful and

gentle animals as they help us feed a hungry world?

Well, first and foremost, we want to create environments that maximize

the welfare and comfort of cows on our farms

Cows that are not comfortable do not produce milk well and

end up costing dairy producers money

Second, we want to produce a wholesome, nutritious product that people can afford

To achieve these goals,

we like to think about the optimal life cycle of the dairy cow in our herd

An easy starting point is birth, or calving

We want to make sure that calves are born into a comfortable and

sanitary environment

And that they consume high quality Colostrum

with in their first 3 hours of life

Now colostrum feeding will be covered in another section

But just as a reminder, colostrum is the first milk the cow produces for

her calf that is rich in antibodies

It is these antibodies that will protect the calf from disease during the weeks and

months of life, while it's own immune system develops

Remember, regular milk or milk replacer are poor substitutes for

high quality colostrum and will not protect your calves from disease

Modern production systems use an immediate or early weaning process where the calf is removed from the mother shortly after nursing colostrum or

immediate if high quality colostrum is provided by a bottle or two

This is done to reduce stress on the calf and the mother

Now you may think that this seems odd that early removal of the calf reduces stress, but it does

Imagine if we leave the calf on the cow for days or weeks and

then separate them, this would be a great stress to the calf and to its mother

Once the calf is removed, it can be individually cared for, and

it is not at rick for injury or disease from mixing with older cows

This newborn calf then enters the equivalent of elementary school where it

is grouped together with other calves of similar age in pens, and transitioned

over several months from a diet of mil or milk replacer, on to solid feed

During this time, it is important that the calf receive all the necessary

vaccinations to ensure that it will be ready to fight disease

These vaccinations vary by location and country, and

you should consult with your veterinarian as to what is recommended in your area Attempting to save money by skipping needed vaccinations is risky and

will likely result in large losses later

Remember, these dairy heifers are the future of your herd and

they should be treated with the utmost care and attention

Now, when is your young dairy heifer ready to take her spot in the milking herd?

Well, this can vary a bit by breed and production system

But I will provide a few key pointers to make sure this first big step

in her productive life is a good one

Before a heifer will lactate or produce milk, she must reach puberty

Now you're not going to need to worry about acne or

who she will be taking to her high school dance like humans

But achieving puberty at the right time is important for profitable dairy production The main goal here is that the dairy heifer is fed an appropriate diet to allow

her to achieve puberty consistent with cows of her breed

How to achieve this will be covered in detail elsewhere in the course

We can define puberty in animals in several ways, but for

dairy cow we define puberty as the age

which she can carry a healthy calf to term with compromising her health

This means that even though some cows may achieve puberty and

start their reproductive cycles at an early age, we need to wait until that

heifer achieves the appropriate size and weight before we breed her

Interestingly, it is a heifer's weight and skeletal size

Now, her age, that has the largest affect on, the age at which she achieves puberty When evaluating heifer's to breed, we need to look at both the skeletal size which,

we typically measure by withers height, or the height at her shoulder and weight

As a general rule, a hosting heifer will start cycling when she achieves about 50

to 55% of her mature body weight

But she will need to reach roughly two thirds of her mature

body weight before she should be bred

In addition, modern Holsteins should be 48-50 inches

to be considered adequately grown for breeding

Frame size and weight are better measures of the physiological age of the heifers

If we only use age as a parameter for

breeding, some heifers may be too small, and others too large

Finally, it should be clearly understood that nutritional status

drives reproductive cyclicity and fertility

So if your not feeding your animals well, they will achieve puberty late and

will have reduced lifetime productivity

Likewise, if you over feed the heifers,

they will also have problems with fertility

In general, our goal is for Holstein to calf and

begin their lactation between 22 and 24 months of age

Of course this is somewhat breed dependant, but it is a good rule of thumb

Now, a heifer calving for

the first time is an animal that should receive careful attention

First of all, she has been in your herd for two years, and

has not generated any income

If something goes wrong at this stage, it is very expensive for the dairy producer Second, although we look forward to each calf the cow gives us, calving is

the most dangerous time in a cow's life and getting your cow successfully through this transition period is the key to profitable dairy production

Once she is calved a two year old heifer must be managed to

deal with the nutritional challenges of high milk production and

also to support body growth which should continue through the next year

Now that we have gotten the heifer to reproductive age

it is important that we take some time to understand basic reproductive anatomy and hormonal control of reproductive simplicity

Both of these are important for

effective management of reproduction in your dairy herd, for example

If you practice artificial insemination or even use bulls to inseminate your cows, understanding how to manage insemination is critical for success

Furthermore, if you plan on using technologies to synchronize your cow herd, you must have an understanding of how hormones affect their reproductive

processes

These topics will be covered in the next lecture

To summarize,

managing the calving process is key to the success of a dairy operation

Calves should be provided with high quality colostrum and

receive adequate vaccinations at the correct times during early life

It is important to remember that cows may start to cycle before they

are of adequate size to conceive and carry a pregnancy successfully to term Remember to focus on body size and weight,

not just age, when making breeding decisions

Cows should achieve two thirds of their mature body weight, and

have adequate skeletal size before breeding

The ultimate goal is to have the heifer calf for the first time between 22 and

24 months of age at adequate body size and

weight to support the demands of continued growth and lactation

Welcome back

Today's lesson will cover the basic reproductive anatomy and

hormonal control of reproduction

As the French physician Fernel once said,

anatomy is to physiology as geography is to history

What the term physiology describes is the study of the body's functions

In this section we are studying the physiology of reproduction

What this quote reminds us is that in order to have a complete understanding of the physiology of reproduction, we must understand reproductive anatomy

So let's take a quick tour through the reproductive tract of the male and

female cattle

The reproductive tract in the female is best visualized as a multilayered tube that connects the ovary to the vagina

The ovary is where oocytes grow, develop, and ovulate

And the vagina is the final tube through which the fully developed fetus passes

As it exits the female reproductive track the egg, or oocyte,

leaves the ovary at ovulation and is picked up by the oviduct

The oviduct is a muscular tube that connects the ovary to the uterus

It is also the place where the sperm and the egg come together at fertilization Now, once the egg is fertilized, it is called an embryo

And early embryonic development begins as the embryo moves down the oviduct into the uterus, a process that takes four or five days

Once the embryo arrives in the uterus, it attaches to the uterine wall and

develops a placenta

The placenta is a tissue that serves as an intermediary

between the fetus and the mother

It attaches the embryo to the uterus, provides critical nutrition and

oxygen to the embryo and produces a number of hormones that are important for pregnancy and the subsequent lactation

At birth, the fetus moves from the uterus through the cervix and vagina and

is delivered as a calf into the environment

Now I will describe the functions of each part of the reproductive tract

starting with the vagina

The vagina is the external opening of the female reproductive tract, and

is the female copulatory organ

It also served as a conduit for urine leaving the body

Beneficial bacteria that inhabit the vagina, also termed commensal bacteria,

produce compounds called pheromones

Pheromones are typically organic acids released from the vaginal bacteria

which the bull can sense with a specialized organ in his nose

The types of pheromones released,

relays information to the bull about the cow's reproductive status

These pheromones are particularly attractive to the bull when the cow is in

Estrus, or heat

Furthermore, the vagina provides the right combination of sensory stimuli for the bull to achieve ejaculation including both temperature and pressure

The vagina is also the site of semen deposition during natural mating, but

not in artificial insemination

I'll tell you more about that later

A common problem of the vagina which can affect fertility is vaginitis or

infection of a vagina

Now, progressing inward from the vagina, we can come to the cervix next

The cervix is the gateway to the uterus

It is a thick, cartilaginous tube, about five centimeters in length,

that controls access to the uterus

The relative openness of the cervix is affected by the stage of the estrous cycle

or gestation

Specific timing of opening and closing of the cervix facilitates

sperm transport as estrous but then closes and protects the uterus during pregnancy For an example there is an abundant secretion of

clear viscus mucus when the cow is in estrous

The presence of this mucus can be used as a secondary sign that the cow is in estrous

And we'll talk more about primary and secondary signs of estrous later

The cervix is also the major barrier for artificial insemination

After estrous, the cervical mucous changes, and

the cervix essentially becomes closed

This is a protective mechanism to stop infections from invading the uterus during gestation

Once inside the cervix the next structure is the uterus

The uterus is essentially two tubes connected at one end,

it's also referred to as the womb

It is the site of attachment and development of the embryo

The lining of the uterus,

known as the endometrium, is designed to develop an intimate association with the fetal placenta that will transport nutrients to the developing fetus

During pregnancy, the endometrium produces secretions called uterine milk

that are taken up by the placenta to support fetal growth

The uterus is surrounded by two layers of muscle,

which it will need at the end of gestation to help expel the fetus at parturition The uterus will undergo tremendous growth in pregnancy

From an organ that you could hold in your two supped hands,

to one that can hold a 40 kilogram calf

At the end of gestation, the muscle layers which were dormant during pregnancy, start to contract in a concerted manner and

ultimately will force the calf through the cervix and vagina at birth

As we continue the journey, the next tube we encounter is the oviduct

Now, the oviduct is a small tube,

about the width of a piece of yarn, that connects the ovary to the uterus

It is the way the ovulated egg gets from the ovary to the uterus

The oviduct is the site where sperm and egg meet at fertilization

After fertilization, the new embryo spends several days in the oviduct completing the journey to get to the uterus

During this time, it undergoes several rounds of cellular division, so by

the time the embryo arrives in the uterus, it is a ball of cells called a morula

The opening of the oviduct is a large,

funnel like structure called the infundibulum that surrounds the ovary and

collects the eggs released at ovulation

Now let's talk about the ovaries

Ovaries are paired structures that contain the female eggs or oocytes

At birth the ovaries contain all the eggs a cow will ever have

Now talk about having all your eggs in one basket,

well I guess two baskets because there are two ovaries

This is different than bulls which can produce sperm throughout their lives and into old age

We refer the eggs and sperm as the female and male gametes, respectively

In addition to the eggs, the ovaries form two other structures that are critical for reproduction

The first are the follicles

Follicles are structures containing the oocyte that grow and

develop in waves during each estrous cycle

They appear as a fluid filled blister on the surface of the ovary,

each one containing an egg

For cows, usually only one follicle ovulates to release its egg every cycle

Although double ovulations are possible

The follicle helps mature the oocyte and it produces the hormone, estrogen,

which prepares the female reproductive tract for the impending pregnancy

Just prior to ovulation, estrogen levels reach their peak and

it is these high concentrations of estrogen

that cause the cow to display the behaviors associated with estrous

Now we'll talk more about these behaviors in a later lesson

You may have noticed the similarities between the words estrous and estrogen Production of estrogen is a physiological adaptation that is designed to synchronize

mating with ovulation, so the sperm and the egg have a greater chance of meeting Bulls are usually very good at detecting changes in behavior and

pheromones that occur during estrous, but humans are not as good and

this can create challenges for deciding which cows to breed

Now, after ovulation and release of the egg, there is a remarkable transformation

of the follicle into a structure called a corpus luteum

After the follicle ovulates and releases it's egg, it stops producing estrogen and then transforms into a large grape-sized structure called the corpus luteum

Corpus luteum mean yellow body

The corpus luteum is a yellowish red color because it contains a lot of beta

carotene, which is the same compound that gives carrots, pumpkins, and

sweet potatoes their color

Beta carotene is an inactive form of vitamin A that the body can activate

to provide this essential vitamin

The primary function of the corpus luteum is to produce the hormone progesterone Progesterone is the most critical hormone supporting pregnancy

You can even see this in the name,

pro gestation, which is another term for pregnancy

Without progesterone pregnancy can not proceed

Progesterone changes the oviducts, uterus, cervix, mammary glands and

brain to prepare them to support the developing embryo

For example, progesterone stimulates secretions in the uterus

that the growing embryo needs and it keeps the muscle layers from contracting until the cow is ready to calf

Another important role for progesterone is that it changes the cow's behaviors Cows with high concentrations of progesterone

don't typically exhibit estrous and will not allow mating

Finally, progesterone acts on the mammary gland to stimulate development

of the secretory tissue in preparation for lactation

So there you have it

The female reproductive tract is a series of tubes including the oviduct that

picks up the egg at ovulation, and is the site of fertilization

The uterus, where the embryo attaches and develops until parturition

The cervix, which is a restrictive passage way between the uterus and

the vagina the seals off the uterus during pregnancy

And the vagina, the copulatory organ of the female and

the common opening of the reproductive and urinary systems

And finally the female gonad or

ovary which contains all the eggs the cow will ever have when it's born

Now that we have taken a quick tour of the female reproductive tract,

let's talk a bit about the male reproductive tract

In modern dairy production, it is getting less and

less common to see bulls on farms,

because greater than 70% of cows in the US are bred using artificial insemination Why is this?

Well, it's quite simple

With the development of artificial insemination, for the first time,

every farmer could own the best bull just by purchasing a straw of his semen Some of the best bulls have sired more than 100,000 calves, and this has greatly accelerated the rate of genetic progress in the national dairy herd

For example, milk production per cow has more than doubled in the last 30 years Now, I can't help but to point out that the many of the techniques associated with artificial insemination were developed and refined here at Penn State in the 1940s and 1950s by a famous scientist named Dr John Almquist

Dr Almquist ultimately was awarded the Wolf Prize for

his work, an award that many refer to as the Nobel Prize for agriculture

He and his collaborators developed and refined ways of freezing and

storing semen

So what was the outcome of all this research?

Well, because of the rapid genetic progress made possible

by artificial insemination

In the US, we have less than a third of the cows than we did 60 years ago

And those cows are producing two-thirds more milk

Added benefits included reducing the spread of venereal disease by bulls,

reducing the cost associated with feeding an animal that weighs almost a ton, and reducing injuries and

deaths associated with having temperamental bulls around workers

Many farmers still have the perception that bull breeding results in the highest pregnancy rates but this is not always the case

Having said that, many farms still maintain live bulls, and

in other countries, it is the primary way that cows get pregnant

There are a number of issues that must be addressed if dairy farmers want to get maximal fertility from their bulls

But first, let's quickly go over the anatomy of the bull reproductive tract

Just as with the ovaries, the testis are also referred to as the gonads, and

there are two of them

The testis are the sites of sperm production

They are housed in the scrotum which hangs away from the body

More about that in a minute

The testis are incredible sperm factories producing in excess

of 10,000 sperm during each heartbeat

Yes, you've heard me correctly, 10,000 sperm per heartbeat

In fact, one mature bull produces enough sperm in one day to fertilize

every cow in the world

Seems excessive doesn't it?

But I will tell you why later

One way we evaluate the fertility of a bull

is by estimating the size of his testes by measuring his scrotal circumference The larger the testis, the more fertile the bull

Testis are similar to ovaries in some ways, but testis are different in that

they will continue to produce sperm throughout the natural life of the bull

Even the oldest bull can fertilize a cow,

even though his fertility declines as he ages

This is the same for humans, where there are reports of males fathering children when they were in their 70s, and even 80s

I sure hope they were up for the midnight diaper changes

Further more, just like an old car that doesn't have the newest features,

old bulls are behind the times with their genetic value for production traits

Further more, breeding bulls to their own daughters should be avoided at all costs This is called inbreeding, and in dairy production it is bad

Even if you use AI,

you want to make sure the bulls you select are not closely related to your cows Therefore, bulls should be replaced on a regular basis, and

AI mating should be carefully chosen by someone knowledgeable about genetics Now, I pointed out that the testis are held outside the body cavity in

the scrotum, which seems to me, and most men, like a dangerous thing to do

Why not keep them nestled inside protection of the body cavity like cows

and women do with their ovaries?

Well, as it turns out,

sperm production cannot take place at body temperature in bulls or men

Now don't ask me why,

it is one of the many mysteries that science has not figured out yet

So the key point here is that the testes temperature is critical to produce high

quantity and quality of sperm

And when it comes to temperature and testis, cooler is better

For maximal sperm production and fertility,

the testis should be 3 to 6 degree centigrade cooler than body temperature

So when you manage your bulls, you must be aware that heat stress, lack of shade or water, and too much activity chasing cows around at hot weather can result in

elevated body temperature that is severe enough to reduce the bull's fertility

And when this happens infertility can last for many weeks

Now, some things you can do if you live in hot climates is to make sure the bulls have easy access to shade and water, and

make sure that you do not have too many cows for each bull to breed

When bulls are young, not more than 10 to 20 cows per bull, and

when the bull is mature, 30 to 40 cows is recommended

Remember, if the cows are spread over large areas,

the bull will have to work much harder

So it is recommended that bulls be housed with cows in smaller pastures during the breeding season

One other trick is to put the bulls in with the cows only at night

when it's cooler

Producing sperm is only one function of the testis

The other important function of the testis is the production of the male sex hormone testosterone

High levels of testosterone are critical for sperm production and for

male sexual behavior

Animals deficient in testosterone will have reduced fertility and

sexual drive, which we call libido

These dud bulls, if not detected and culled,

can greatly reduce pregnancy rates on farms that rely on bull breeding

Now, once the sperm are produced in the testis,

they have to travel a long way to make it out of the body and into a cow

The major tube leaving each testis is called the epididymis

If the testis are like sperm production factories, the epididymal tubes are like finishing shops that take the sperm from the testis and

put the finishing touches on them for maximum fertility

The epididymis also serves as a storage site where the sperm collect

until ejaculated

It takes about two weeks for sperm to traverse the epididymal ducts, but

by the time they do, they are fully mature and ready to go

One other point

Just like we often reach to the back of the grocer's milk case to get the freshest milk, sperm that spend too long in the epididymis can start to age and

lose fertility

Therefore, when a bull has not ejaculated in a long time,

the first couple of ejaculations will likely have reduced fertility as

the old sperm are cleared from the epididymis first

From this storage depot in the tail of the epididymis, the sperm are recruited to move into the vas deferens when the bull is preparing to ejaculate

Each epididymal duct is connected to its own ductus deferens, or vas deferens The vas deferens is a muscular transport tube that carries sperm from

the epididymal duct back up into the body cavity in preparation for ejaculation Guys, this is the tube they cut when you get a vasectomy

Severing these two tubes essentially blocks movement of sperm into the penis for ejaculation

This is a very effective and safe method of birth control

As the sperm move through the male reproductive tract,

several accessory sex glands add key components to the sperm to nourish and protect them during the journey

The accessory sex glands, which include the seminal vesicles, the prostrate and the bulbourethral glands add essential nutrients, buffers, antibiotics,

and other molecules to the sperm from the testis

to help them on their long journey through the female reproductive tract

These glands also give you ejaculate its volume,

which in the bull, is about three to five milliliters, or

about a teaspoonful, and about a billion sperm per milliliter

The sperm and the accessory fluids together are referred to as semen and

this gathers near the base of the penis just prior to ejaculation

Now the penis is the sperm delivery mechanism that conveys the semen, which is the sperm and the accessory fluids to the sight of semen deposition in the cow, which is the deepest part of the vagina, just outside the cervix

Now if you remember from above, I told you that fertilization takes

place in the ova-duct, and this is a long way for a sperm to travel

To make a comparison,

it would be like a six foot tall man walk 100 miles through a mountain range

More on that journey later

For the male, the testis are the sperm factories that also produce testosterone

They must be kept cooler than body temperature to function

The sperm, 10,000 per heartbeat, leave the testis and are finished and

stored in the epididymis until ejaculation,

at which time they move up into the body through the vas deferens

And passed the accessory sex glands, which add protective secretions to the sperm

that help it survive in the female reproductive tract

The sperm and accessory fluids are called semen

And together, they are expelled from the penis into the vagina at copulation

Well, that was a lot to cover in one lesson

But I hope you have a better understanding of the anatomy and

function of the male and female reproductive tracts

In the next lecture,

we're going to tell you about how hormones regulate reproductive processes, and

describe the changes that occur during the estrus cycle of the cow

The Estrous Cycle

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[MUSIC]

Welcome back, in the previous lecture we covered reproductive anatomy, and

function of the male and female reproductive tracks

In this lecture,

we're going to tell you about how hormones regulate reproductive processes and describe the changes that occur during the estrous cycle in the dairy cow

The story of the estrous cycle is really a story about

two primary structures on the ovary and two hormones

The structures on the ovary are the follicles which produce the egg or

oocyte, and the hormone estrogen

The other structure is the corpus luteum which produces the hormone, progesterone The growth and ovulation of a follicle and the growth and regression of corpus luteum define the structural changes on the ovary that occur during one reproductive cycle

As each structure grows it produces more and more of its hormone either estrogen or progesterone

And then this hormones act when the reproductive tract to prepare the cow for

pregnancy, and on the brain to drive the behaviors that will first ensure mating

at the appropriate time, and then stop cyclicity once pregnancy is established

The average estrous cycle length in dairy cows is approximately 21 days, and

is defined as the length of time between subsequent periods of estrus or heat

So, what is this heat we speak of?

Well, we define estrus as when the cow will allow mounting by other cows or

accept the bull for mating

In fact, we often say the cow is in standing heat or

standing estrus because of this behavior

It is important to understand that this behavior has an essential purpose

It is designed to time mating or insemination with ovulation

with the goal of bringing the sperm and the egg together for fertilization

When thought of this way, it makes sense that this behavior is tied to the cycle of growth of follicles on the ovary, and that, as the follicle is ready to be

ovulated, the cow's behavior will change to promote mating

This change in behavior is driven by increasing concentrations of

estrogen coming from the follicle as it matures

Once estrogen reaches its peak concentrations,

the cow will exhibit distinct signs of the pending ovulation

These signs will first be apparent as restlessness,

an increase in vocalization, interactions with other cows,

resting her chin on the backs of other cows, and attempting to mount other cows These behaviors are referred to as secondary signs of estrus and

are common just prior to, during, and just after estrus

During the period before the onset of standing estrus,

the cow will not allow other cows or the bull to mount her

Once, however, final maturation of the follicle occurs and peak estrogen levels are achieved, she will now stand to be mounted by other cows or a bull

This period of standing heat is designated as day 0 of the estrous cycle and will last between 6 and 24 hours

Young heifers tend to exhibit longer periods of estrus around 12 to 15 hours And mature lactating dairy cows will exhibit shorter periods of estrus

around 6 to 9 hours

These averages are for US Holstein cows and

other breeds of cattle may exhibit slightly different averages

It is important to remember that cows exhibit estrus around the clock, so

if your only checking cows infrequently,

you are likely to miss the cow standing estrus

More on how to accurately detect estrus later

Now once the cow enters standing estrus,

she will ovulate about 30 hours later after she is no longer in estrus

This stage of the estrous cycle,

from the end of estrus until the mature corpus luteum forms on the ovary and progesterone can be measured in the blood, is called metestrus

During metestrus, ovulation occurs and

the oocyte starts its journey down the oviduct to the uterus

The follicle which has ruptured and released the oocyte then undergoes

a remarkable transformation to form a corpus luteum which secretes progesterone Remember, progesterone is the key hormone of pregnancy and pregnancy cannot be maintained unless there's an adequate supply of progesterone

If a successful pregnancy is going to be established,

the oocyte will need to be fertilized during metestrus in the oviduct

By the end of metestrus, around days four to five of the estrous cycle,

the fertilized embryo will enter the uterus and

the cow will enter the next stage of the estrous cycle called diestrus

Now diestrus is the longest stage of the estrous cycle,

lasting from about day 5 until about day 18

And the dominant ovarian structure is the corpus luteum,

which produces large amounts of progesterone

Progesterone acts to prepare the reproductive tract for establishment and

maintenance of pregnancy and will work on the cow's brain to block ovulations and estrus behavior as long as the corpus luteum is present and

is producing progesterone

So, the embryo arrives in a uterus that was first primed by estrogen and then by

progesterone to find an environment ideal for establishment of pregnancy

During this time,

the embryo must begin signaling the uterus to maintain the corpus luteum

It does this by releasing hormones that reveal its presence, and

act on the uterus and ovary to protect the corpus luteum

The signals termed pregnancy recognition signals

emanate from the early embryo starting at around day 13 of the estrous cycle

One of the key signals produced by the cow embryo is a hormone called

interferon tau changes the function of the uterus and insures that the corpus luteum will continue to function and produce progesterone

Now, if the oocyte was not fertilized or

if the early embryo failed to develop correctly and produced interferon tau,

dramatic changes will occur that will result in death of the corpus luteum

This is a process termed luteal regression

This process is mediated by a hormone called prostaglandin F

Prostaglandin F is released by the uterus at the end of diestrus

travels to the ovary and kills the corpus luteum

The utility of prostaglandin F in regulating reproductive cycles

was first recognized in the 1960s and 70s

And it soon was available commercially to synchronize estrous cycles by causing cows

with a corpus luteum to regress their CL and return to estrous

Regression of the corpus luteum is initiated a non-pregnant cows around day

18 of the estrous cycle and is accompanied by a rapid decline in progesterone This marks the onset of proestrus, the final stage of the estrous cycle

With progesterone at low levels, signals emanating from the cows brain will cause another follicle to grow over the next three days, and

begin to produce increasing amounts of estrogen

This process will continue as described above, and

the cow will come back into estrus, beginning her next estrous cycle

So when cows reach puberty, they will exhibit periods of standing estrus

every 21 days, until they are successfully inseminated and establish a pregnancy The challenge for dairy producers is to accurately detect estrus and

to time insemination, so that viable sperm are present in the oviduct

when the freshly ovulated oocyte arrives during metestrus

If the farm is using bulls to breed cows

these bulls will be constantly be monitoring cows for estrus and

will repeatedly mate with cows in standing estrus

If the farm, however, is using artificial insemination then the farmer must learn to accurately detect estrus to time the insemination with ovulation

This is a much harder task and will be covered in the next lecture

To summarize, the estrous cycle of the cows is a story of growth and

ovulation of a follicle on the ovary

That is accompanied by a production of estrogen

that will peak just prior to ovulation

High concentrations of estrogen will cause the cow to first

exhibits secondary signs of estrus,

including restlessness, vocalization, chin resting, and mounting other cows These behaviors will occur just prior to, during, and just after the end of estrus Standing estrus marks day 0 of the 21 day estrous cycle, and

indicates that ovulation will shortly occur

Cows ovulate during metestrus and following ovulation,

the ruptured follicle forms into a corpus luteum and secretes progesterone Once progesterone reaches high enough levels to be detected in the blood, the cow enters diestrus, which is the longest stage of the estrous cycle

If a fertilized embryo arrives in the uterus and develops appropriately,

it must begin to produce interferon tau by about day 13 of the estrous cycle

to rescue the corpus luteum and insure continued progesterone production

If there is no embryo, the corpus luteum will regress and

initiate the onset of proestrus

This will cause progesterone concentration to drop sharply

And allow another follicle to grow and ovulate to initiate a new estrous cycle

In the next lecture, we'll cover factors affecting expression of estrus and

strategies to accurately detect estrus and

insure timely insemination of your dairy cows

Detecting Estrus

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[MUSIC]

Hello, now that you know a bit about the estrus cycle of the cow,

let's focus on challenges of detecting estrus or heat, and inseminating cows at

the appropriate time to maximize the chances of establishing a pregnancy

Heat detection is important in the US,

because the majority of cows are bred by artificial insemination

Remember from our discussion of the life cycle of the cow, after she calves,

we give the cow roughly two months to adjust to the demands of lactation and

to heal her uterus in preparation for the next pregnancy

We want cows to calve roughly every 12 to 13 months for profitable dairy production

In order to accomplish this, dairy farmers must be good at detecting estrus

However, there is a wide variation in the ability of dairy workers to

accurately detect heats, and in many cases,

they will detect less than 50% of heats in their herds

Even worse, in some cases, cows are called in heat that are not in heat

When this happens you not only lose time, but

money is wasted on insemination that will not result in a pregnancy

This can be a real problem for getting cows pregnant in a timely fashion

Now, if the farm uses bulls to breed the cows,

heat detection is done by the bull, which is housed with the cows

Bulls are generally considered to be much better at detecting heat

in cows than humans are, which should be no surprise to anyone

So you might be asking, well, if heat detection is so difficult for humans and bulls are so good at it, why not just use bulls to breed all the cows?

Well, there are a number of reasons why bull breeding is not desirable

First and probably most important, is that a farm's ability to improve the genetics

of their cow herd will be reduced if they use bulls for breeding

Adoption of artificial insemination

has allowed the dairy industry to rapidly improve the genetic value of dairy cows This is because every farmer can now purchase a straw

of semen from the best bull

For example, in the US, we are producing two-thirds more milk today

than we did 60 years ago, and we're doing it with about one-third of the cows This is because of the increased genetic value for milk production

that resulted from widespread adoption of artificial insemination

Now, this increased milk production has greatly reduced the environmental impact

will occasionally become infertile

Finally, bulls are unpredictable, and

every year we hear stories of people being injured or killed by bulls

For these reasons, most dairies use artificial insemination, and

accurate heat detection is a key component to a successful AI program

Like every challenge,

to overcome it we must break the challenge down into its essential elements First, we need to inseminate cows after they come into estrus, but

before they ovulate

Research has shown that cows will ovulate about 30 hours from

the point they enter estrus

The problem is that we rarely know exactly when a cow comes into heat Current recommendations for heat detection stipulate

that dairy personnel should watch cows three times a day for 30 minutes, especially during times when cows are moving to and from the milking parlor Now, this recommendation is rarely adopted, because farmers are busy and often multitask heat-checking with other duties on the farm

Furthermore, cows in modern dairies are often housed in barns with concrete floors that can be slippery

This will discourage cows from mounting other cows or

allowing other cows to mount them

In hotter climates, it is essential that cows are cooled with fans or

water sprinklers,

because hot cows will not exhibit signs of estrus, especially during the day Cows that have feet or leg injuries, or that are losing weight due to

the demands of lactation, will also not show signs of estrus

If you remember, I mentioned previously that cows come into heat during all hours of the day and night

So how often are cows being watching during the night?

If a mature cow comes into heat at 9PM,

she might be out of heat by 6AM the next morning

Thus her entire cycle will be missed, and her breeding will be delayed

Finally, it is important to remember that signs of heat covered in the last lecture, including increased activity, vocalization,

chin resting, mounting other cows and

evidence of mucus discharge are all called secondary signs of estrus

And they can be seen before, during, and after a cow is in heat

The defining sign that a cow is in heat is that she will stand for

several seconds when being mounted by another cow or a bull

Ideally, this is what is used to make a decision to inseminate a cow

>> Let's focus in on the period of heat itself and

the signs of heat that may occur prior to or during heat

The primary and

most reliable sign is that the cow stands to be mounted by another animal

A cow that is not in heat will quickly walk away, if an attempt is made to mount her, or she may turn and butt the cow attempting to mount her

A cow standing to be mounted is the only accurate sign of of estrus

Other signs, called secondary signs, which are less reliable, but

are good clues that heat may be near, include mounting other cows

These cows may or may not be in heat

Mounting other cows may be a sign that they are approaching heat

These cows should be observed closely for other behavior, like a clear

mucous discharge from the vulva and swelling and reddening of the vulva

Persistent trailing and attempting to mount other cattle and

less time resting, bawling, and general excitement and nervousness

Tail head hair that has rubbed off or fluffed off, and

dirty flanks, sniffing the genitalia of other cows, head raising and

lip curling, and chin resting and rubbing the backs of other cows

>> Once the cow is detected in standing estrus,

it is important to inseminate that cow such that the sperm have time to travel

to the oviduct prior to the arrival of the ovulated egg

Remember, fertilization takes place in the oviduct

As a general rule, we say that sperm have a life span of about 24 hours in

the female reproductive tract

And that the egg has a life span of about 12 hours after it is ovulated

Remember, we know that a cow will ovulate roughly 30 hours after she enters estrus Yet we almost never know the precise time when the cow first entered estrus

So the best recommendation is that cows detected in estrus

should be inseminated as soon as possible, within the next couple of hours

If the farmer knows precisely when the cow entered estrus or

stood to be mounted, then we use what's called the AM/PM rule

The AM/PM rule states that if a cow is first detected in estrus in the morning,

then breed her that afternoon

And if she's first detected in heat in the afternoon,

then breed her first thing the next morning

Once again, the AM/PM rule works well when the farm

feels confident they know when the cow first entered estrus

If the cow is seen in heat first thing in the morning,

it is possible that that cow came into heat the night before

In this case, our first recommendation should be followed, and

the cow should be bred as soon as possible

To summarize, accurate estrus detection is a key component

of artificial insemination breeding

The goal is to have viable sperm in the oviduct when the egg arrives

shortly after ovulation

To accomplish this, we need to breed cows towards the end of estrus, a period of time that can be as short as six to nine hours in mature, lactating dairy cows However, we often don't know precisely when the cow first came into heat Therefore, we recommend that cows detected in estrus should be bred as soon as possible, unless it is known when the cow first came into heat

Then we recommend that cows detected in heat in the morning are bred in

the afternoon, and

those detected in the late afternoon are bred the following morning

This is called the AM/PM rule

Of course, all of this relies on accurate estrus detection

Secondary signs of estrus including increased activity, vocalization, chin

resting, and mounting other cows are good signs that the cow is close to estrus However, a definitive diagnosis of estrus is that the cow will stand for

several seconds when mounted by another cow or a bull

To detect estrus accurately, farms should conduct dedicated heat detection at least

three times per day for 30 minutes each time

Personnel tasked with estrus detection

should have this as their primary duty during this time,

and the cows should be in a comfortable, cool environment with good footing

In the next lecture, we wrap up our module on reproduction with a discussion

of factors affecting conception rate and how to detect pregnancy

Welcome back

As we wrap up this module on reproduction,

we're going to focus on the key question in any reproductive management program Did we get the cow pregnant?

Pregnancy rate is the key metric to measure the effectiveness of

a reproductive management program

Pregnancy rate is calculated by measuring heat detection rate by conception rate For example, if heat detection rate is 50% and

conception rate is 40%, then pregnancy rate will equal 20%

In the last session we talked about the challenges of heat detection and

how to improve heat detection rate

Many dairies address the problem of low heat detection rate

by incorporating ovulation synchronization and

timed insemination into their reproductive management programs

In these programs, cows are induced to ovulate in a tight window, and

they can be inseminated on a schedule without heat detection

The advantage of these programs is that the first part of the pregnancy rate

calculation, heat detection, is replaced with a new term called submission rate This represents the fact that all cows that are started

on an ovulation synchronization program are submitted for

insemination regardless of whether they exhibit signs of estrus

In our example, if heat detection is replaced by submission rate of 100%,

the new pregnancy rate would be 40%

Which would be outstanding and well above the national average for

pregnancy rate of about 17 to 19%

Of course in the real world, we rarely achieve 100% in anything we do

However, I think you can see the beneficial effects of

increasing the number of cows submitted for insemination

Now, the details of how to accomplish effective

ovulation synchronization programs are beyond the scope of this MOOC

But many dairies in the U.S use a combination of insemination based on

detected heats and timed insemination following ovulation synchronization

Once cows are inseminated, the second part of the equation becomes the critical determinant of pregnancy rate, that is, conception rate

Now, conception rate is affected by a number of factors, and

these factors are under varying levels of control by the farmer

The factor that is most difficult to change quickly

is the inherent fertility of your cows

Yes, it's true, cows differ in their genetic value for fertility

We see differences between breeds, and

within breeds we see differences between cows

Because this trait is controlled by genetics,

we can improve the genetic value of our herd for fertility traits

But this takes careful attention and time and will not be accomplished overnight The value of including fertility traits in selection of our breeding stock

was recognized over 40 years ago

But only seriously addressed after many breeds were experiencing lower fertility Now, modern selection programs are including

fertility traits in their selection indexes and

we are seeing the genetic value for our fertility traits increasing

You will find more information on genetic selection in the section

on dairy genetics

There are other factors which influence conception rate that are under greater control by the dairy

For example, we discussed in the last section that accurate heat detection

was critical to achieve maximum pregnancy rates

If cows are not inseminated at the correct time,

they have little chance of fertilization and conception rates will be low

Likewise, if ovulation synchronization programs are not optimized,

conception rates will be low

In both cases, careful attention to detail, training and

retraining are essential

Secondly, cows submitted for insemination must be healthy and

live in comfortable environments

For example, cows that are losing weight will have reduced conception rates Cows that have subclinical diseases, including mastitis and

ketosis, will have reduced conception rates

Cows that have chronic feet and

leg problems will have reduced conception rates

Cows that are heat stressed will have reduced conception rates

I think you get my point

Healthy, comfortable cows are the most important element

of a successful reproductive management program

When healthy, comfortable cows are inseminated at the appropriate time

with sperm from high quality bulls,

the cows will have the ability to express their genetic potential for fertility and deliver a healthy calf in a little over nine months

One other issue to be aware of is that humans can

often be the primary stressors in a cow's life

Good dairy farmers work hard to ensure that cow-human interactions are as stress-free as possible

This means training workers to move gently and quietly among the cows and

to handle them with respect and care

As JD Hoard, founder of the Hoard's Dairyman Magazine said

more than 125 years ago, cows are the foster mothers of the human race

There should be zero tolerance for neglect, rough handling or

abuse by workers and poor treatment of cows by just

one worker is an affront to the entire dairy industry

Gentle handling and reduced stress on cows is particularly important during the first

4 to 6 weeks of pregnancy

This is a time when most pregnancies are lost and

the developing embryo is very sensitive to stress

For example, heat stress kills many embryos in the first week after conception

and every effort should be made to reduce heat stress in your cows

Other stressors include, remixing cows in pens,

transportation, handling for management, especially things like hoof trimming All these can cause early embryo loss

Once cows are inseminated, they need to get through this critical window

stress-free in order to maximize fertility

Now, I'm going to close this module with a brief discussion about

pregnancy detection

For dairy producers,

results from pregnancy checks tell them a lot about how they're managing their cows And if conception rates are low,

this will have a long term effect on the profitability of the dairy farm

There are several ways that are used to detect pregnancy

Of course, the most obvious is that cows that fail to conceive

may exhibit estrus 18 to 24 days after they are inseminated

If this is the case, it is important to ensure that cows

are truly in standing estrus, and not just exhibiting a secondary sign of estrus,

which occasionally occurs in cows that are actually pregnant

Interestingly, many cows that fail to conceive will not exhibit estrus in that

18 to 24 day window and some may not exhibit estrus for 1 to 2 months

We see this especially in high-producing dairy cows

that were inseminated using an ovulation synchronization program

Of course dairies that struggle to attain high heat detection rates

will be especially affected in this regard

Most commonly dairy producers will use transrectal palpation

to detect pregnancy in their cows

It is recommended that this technique be done after 35 days following insemination Attempting to palpate pregnancies before 35 days has the potential to induce

pregnancy loss

There are also several blood tests that are available to detect

pregnancies as early as 28 days after insemination

Finally, transrectal ultrasonography in the hands of a skilled professional is

probably the best approach to detect pregnancy

because fetal heartbeat can be confirmed

This technique is effective starting around day 28 after insemination, but

it can be costly

The goal with pregnancy detection is to identify as early as possible

those cows that failed to conceive so they can be re-inseminated

The interval between inseminations is one way to evaluate the effectiveness of your pregnancy detection program

Current recommendations are that the interservice interval, or the time between two inseminations, be less than 42 days or about 2 complete estrous cycles

Finally, once a cow is detected pregnant,

it is important that her pregnancy is confirmed later in gestation,

especially if the first pregnancy test is done very early

In US Holstein cows,

as many as 10 to 15% of confirmed pregnancies are lost by day 60

Therefore, we recommend that cows are re-checked

around day 60 after insemination, and at least once again after day 90

Many producers will incorporate an additional pregnancy check beyond this to ensure cows are pregnant at dry off

As we wrap up this module on reproduction, let's remember a few key points

First, optimal dairy production relies on making management decisions that allow your cows to express their genetic potential

Perhaps the biggest factor to this end is that cows must be in comfortable

environments, and they must be managed by workers who care about their health and well-being

We want cows to freshen and join the milking herd for

the first time at about two years of age, with an adequate body size to accommodate the stress of birth and the subsequent lactation

We would like our cows to be able to complete the cycle at least four to six

times before we replace her in the herd with a new heifer

Utilizing reproductive management programs effectively requires an understanding

of the anatomy and physiology of the male and female reproductive tracts

This will help workers understand the factors that control the estrus cycle, and

the willingness of cows to exhibit estrus

If farms want to incorporate programs that rely on ovulation synchronization and timed insemination

It is even more important that the workers have a clear understanding

of the effects of the hormones used in these programs on the cow's physiology The primary metric for

evaluating reproductive management on a dairy is calculating the pregnancy rate, which is the product of heat detection rate and conception rate

There are tools available to improve both these factors, but these tools

require careful training, retraining, and monitoring to work effectively

Finally, early detection of pregnancy status following insemination

will allow for rapid re-insemination of those cows which failed to conceive

Well, that's all for this module

Thank you for your participation, and

I hope you increased your knowledge about dairy reproduction

I encourage you to keep the Penn State Extension web page

bookmarked on your web browser, and be on the lookout for new and

more advanced offerings in each of the areas covered in this MOOC

number of cows inseminated

number of cows in heat

number of cows ovulating

number of cows pregnant

Cows losing weight

All of the above

7.Question 7 Which of the following is the most accurate description of when a Holstein heifer isready to be inseminated for the first time?

1 / 1 point

As soon as the heifer exhibits a good standing estrus

When the heifer is two years of age

When the heifer is cycling and achieves 2/3 of her mature body weight and a withers height

10 Question 10 What is recommend times and intervals for heat detection 1 / 1 point

Once per day for 20 minutes

Twice a day for 30 minutes

Three times per day for 30 minutes

Four times per day for 10 minutes

Correct

11 Question 11 Which is not a benefit of using artificial insemination? 1 / 1 point

Reduce venereal (sexually transmitted) diseases

Simple and can be done without training

Reduced costs compared to bull breeding

Reduced injuries to cows and personnel

Mounting other cows

All of the above

Mounting other cows

Standing to be mounted by other cows

Quy tắc AM / PM: Liên quan đến thời điểm thụ tinh nhân tạo, những con bò phát hiện bị động

dục vào buổi sáng nên được phối giống vào buổi chiều và những con bò phát hiện bị động dục vào buổi chiều nên được phối vào sáng hôm sau

Kháng thể: Các globulin miễn dịch được hấp thụ bởi dạ dày của bê và cung cấp khả năng miễn

dịch trong những tuần đầu tiên sau khi sinh của bê

Tuyến sinh dục : Tuyến phụ góp phần sản xuất huyết tương.

Cổ tử cung: Ống sụn nối tử cung với âm đạo.

Nằm yên : Dấu hiệu động dục phụ khi một con bò cái sẽ tựa cằm vào lưng một con bò khác Sữa non: Sữa đầu tiên mà bò tạo ra cho bê con rất giàu kháng thể

Tỷ lệ thụ thai: Số bò cái có chửa chia cho số bò cái được thụ tinh.