coursera week 6 DAIRY PRODUCTION AND MANAGEMENT

Glossary
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
Share
0:00/9:27

Share
Help Us Translate
Interactive Transcript - Enable basic transcript mode by pressing the escape key
You may navigate through the transcript using tab. To save a note for a section of text press
CTRL + S. To expand your selection you may use CTRL + arrow key. You may contract your
selection using shift + CTRL + arrow key. For screen readers that are incompatible with using
arrow keys for shortcuts, you can replace them with the H J K L keys. Some screen readers may
require using CTRL in conjunction with the alt key


[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
Share
0:00/9:26


Share
Help Us Translate
Interactive Transcript - Enable basic transcript mode by pressing the escape key

You may navigate through the transcript using tab. To save a note for a section of text press
CTRL + S. To expand your selection you may use CTRL + arrow key. You may contract your
selection using shift + CTRL + arrow key. For screen readers that are incompatible with using
arrow keys for shortcuts, you can replace them with the H J K L keys. Some screen readers may
require using CTRL in conjunction with the alt key
[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
of dairying.
This rate of genetic progress would not have been possible with bull breeding.
Another reason is the cost of purchasing and
maintaining a bull, which can amount to several thousands of dollars per year.
Bulls can also carry and spread venereal disease, and


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