4 Physiology Review: The Estrous Cycle and Synchronization

OVULATION; DAY 0

1. LUTEAL PHASE: Metestrus; Day 1-4. An ovulatory follicle ruptures to release an egg forming a Corpus Hemmorhagicum. This turns into a Corpus Luteum (this is called lutenization) which produces progesterone, the hormone to inhibit repro. behavior and maintenance of pregnancy. So, progesterone begins to increase.

2. LUTEAL PHASE: Diestrus; Day 4-18. Corpus Luteum is fully functional and progesterone plateaus. During the last 2-3 days, destruction of the Corpus Luteum occurs (this process is called luteolysis) due to Prostaglandin F2alpha. This terminates the Luteal phase.

3. FOLLICULAR PHASE: Proestrus, Day 19-behavioral estrus. Progesterone is decreasing after luteolysis and estradiol becomes dominant hormone. GnRH SURGES, triggering LH and FSH.

4. FOLLICULAR PHASE: Estrus. Female sexual receptivity. Peak Estradiol and LH/FSH secretion (which grows and matures follicle) causes ovulation.

A LONG ONE: Starting and ending at ovulation, use the names of the phases, hormones in each phase, and describe what happens during the estrous cycle

Day 0: estrus

Day 1-4: metestrus

Day 4-18: diestrus

Day 19-behavioral estrus: proestrus

Cows have non seasonal polyestrous cycles (meaning they cycle multiple times year round) = cycle ranges from 17-24 days

Describe the days of the bovine estrous cycle

Estrus is the sexual receptivity of the female. SHE WILL STAND to be mounted and has clear vaginal mucus discharge. Inc. bellowing and walking, dec. rumination/milk production. TONED uterus

What is estrus? Name some behaviors typically seen in estrus

Estrus

Which stage of the estrous cycle is the sexual receptivity of the female. SHE WILL STAND to be mounted and has clear vaginal mucus discharge. Inc. bellowing and walking, dec. rumination/milk production. TONED uterus

Peak estradiol levels

What hormones are highest during estrus? What is the follicle like?

xx

For your reference

Fluid filled structures on the ovary that release the egg

During estrus there is follicle maturation, and final follicular maturation occurs in metestrus. What IS the follicle?

Final follicular maturation and ovulation (where the follicle bursts to release the egg, which is ovulation that starts into metestrus), forming a corpus luteum (which is the result of the follicle bursting, releases progesterone to prepare the womb for pregnancy)

What major processes occur during metestrus?

Metestrus

During which stage of the estrous cycle is final follicular maturation and ovulation (where the follicle bursts to release the egg that starts this part of the estrous cycle), forming a corpus luteum (which is the result of the follicle bursting, releases progesterone to prepare the womb for pregnancy)

Progesterone levels are the highest. Period of corpus luteum dominance thru luteolysis (aka degradation of the corpus luteum). Uterus FLACCID

What major processes occur during diestrus?

Diestrus

During which stage of the estrous cycle are Progesterone levels the highest. Period of corpus luteum dominance thru luteolysis (aka degradation of the corpus luteum). Uterus FLACCID

Progesterone levels are decreasing and estradiol levels are increasing. This is when cows start to mount.

What happens during proestrus?

Proestrus

During which stage of the estrous cycle are Progesterone levels decreasing and estradiol levels increasing. This is when cows start to mount.

The first follicular wave occurs as Progesterone is rising or during peak secretion. So, follicles during this wave will become atretic (they degenerate)

This will also happen during the second wave if the cow has three total

What happens during the first follicular wave in cattle? (most have 2-3 waves) When does this occur?

The third follicular wave is initiated before luteolysis (when the CL regresses) and a dominant follicle will ovulate. Only follicles in growing phase during luteolysis can ovulate.

What happens during the final follicular wave in cattle? (it may be the third or second wave depending on the cow) When does it happen?

When she reaches 50-65% of her adult body weight

When do heifers generally hit puberty?

Genotype (Bos Taurus earlier than Bos Indicus), *body weight*, nutrition

Name the factors that influence puberty in cattle?

BEEF: 600-650 lbs, 9-12 months

DAIRY: 700-750 lbs, 10-15 months

At what age and weight do beef and dairy heifers hit puberty?

6-30 hours (normally around 15 for dairy, 20 for beef)

How long does estrus last in cattle?

Ovulation occurs 2-20 hours after the end of estrus, after estrogen has peaked

When does ovulation occur and how long does it last?

BEEF: most are bull bred with light calving intervals

DAIRY: most AI bred and year round calving

What is the difference of insemination between beef and dairy herds?

Heifers are bred at 14-15 months of age and calve at 22-24 months of age

When do you breed dairy heifers and when do they calve?

The calf is removed at birth then fed colostrum and hand reared

After dairy calves are born, what happens to them?

Her calf is removed from her side, she enters milking herd. The has a voluntary waiting period during which she will not be bred. After this period is over, she enters the breeding group

What happens to a cow after she births a calf?

45-65 days

During the voluntary waiting period, a cow that has just calved will not be bred. How long is this period typically?

She needs to be observed in heat and inseminated. Once heat is detected and the animal is bred, this is DAYS TO SERVICE (it doesn't matter if the insemination is successful or not)

A cow has moved thru her voluntary waiting period. Now what?

75 days = gives a picture of heat detection or anestrus (if number is increased, then animals are not cycling or not being detected cycling)

What is the average "days to first service" in cows, the period from calving to first breeding? Why do we care about this?

40% or greater

What should the conception rate be on the first service?

Few cows should have extended days open (days not pregnant)

If both estrus detection and conception rates are adequate, then few cows should have WHAT?

1. inadequate estrus detection

2. poor expression of estrus (due to heat stress, concrete, or feet and legs)

3. high number of anovulatory cows during early lactation

Why are service rates poor in dairy cattle? (remember this is when heat is detected and animal is bred for the first time)

a. inadequate estrus detection

b. poor expression of estrus

d. high number of anovulatory cows during early lactation

Select the reasons why service rates are poor:

a. inadequate estrus detection

b. poor expression of estrus

c. bull semen inadequate

d. high number of anovulatory cows during early lactation

e. inability to stay pregnant due to CL regression

1. high incidence of early embryonic death during early gestation

2. estrus detection errors

3. semen quality

4. AI technique

5. bull fertility

6. milk production and nutrition

7. environmental influences (temp.)

8. age

9. genetics

*Why might conception rates be poor in dairy cattle?*

a. high incidence of early embryonic death during early gestation

b. semen quality/bull fertility

d. milk production/nutrition

f. estrus detection errors

Select the reasons why conception rates might be poor in dairy cattle:

a. high incidence of early embryonic death during early gestation

b. semen quality/bull fertility

c. medications

d. milk production/nutrition

e. number of animals in pasture

f. estrus detection errors

We have bred so much for milk production that we have decreased conception rate

First service conception rates has decreased in dairy cattle, why?

herd members detected in heat and inseminated (A) x AI technique (B) x fertility level of herd (C) x semen fertility level (D) = % pregnant

What is the equation of reproduction?

Less than 2.5

How many services are required to achieve pregnancy commonly?

The duration of estrus of a cow milking 60 lbs per day has an average time of *14.7 hours* in standing heat (cows standing to be mounted)

The duration of estrus of a cow milking 60 lbs per day has an average time of how many hours in standing heat?

As milk production increases, standing heat decreases drastically

How does milk production affect standing heat in cattle?

pregnancy rate = estrus detection rate x conception rate

so we have to inc. one of those or both of those factors

How can we increase pregnancy rate?

1. tail-head pressure monitors

2. estrus detector animals

3. pedometry (a step recorder, because remember cows walk around more in estrus)

4. vaginal fluid electrical resistance decreases during estrus

List estrus detection aids

Heat detection (ex. personnel missing the signs of heat detection)

What is one of the largest reasons for dec. pregnancy rates in cattle?

1. proper cow ID

2. separate into and observe small groups for heat

3. proper nutrition

4. good footing

5. maintain accurate records

6. train/assign heat detection to one person

7. use estrus synchronization programs

8. use estrus detection aids

Describe the factors we can use to enhance estrus detection

a. proper cow ID

b. use estrus detection aids and synchronization programs

d. train/assign heat detection to one person

f. maintain accurate records and good nutrition

Choose the factors we can use to enhance estrus detection:

a. proper cow ID

b. use estrus detection aids and synchronization programs

c. breed all with the same semen

d. train/assign heat detection to one person

e. use cows of the same breed

f. maintain accurate records and good nutrition

Tail head pressure monitors

This type of estrus detection aid includes Kymar (kind of like an ink sac that explodes when something mounts the cow), lotter tickets, tail paint, chalk, and Heatwatch

Estrus detector animals

This type of estrus detection aid includes chin ball markers (when the animal with the chin marker mounts another animal, it will mark the animal that is being mounted), gomer/teaser bulls (vasectomized), androgenized heifer/steer

Chin ball for estrus detector animals

What is this?

Tail head pressure monitors

What is this?

OvSynch and CIDR (intrauterine device that releases progesterone) Synch

=these are both TIMED AI PROTOCOLS

Note: CIDR is progesterone but considered an Estrus control because you are controlling when they go into estrus when you pull it

What are the primary Estrus Control or Synchronization programs used to improve service rates in dairy cattle?

Use Timed AI protocols (OvSynch or CIDR Synch) = service rate is now 100% because all eligible cows were bred

Timed AI allows producers to perform insemination at fixed time without the need of estrous detection

How do you remove heat detection from the equation of pregnancy (the BIGGEST error in getting them pregnant)?

We are more controlling diestrus, but in this way we can hasten or delay the onset of estrus

What is "control" of the estrous cycle

Coordinated and control of estrus in multiple animals

What is "synchronization" of the estrous cycle

1. reduce window of time when insemination is appropriate

2. reduce time spent on estrus detection

3. enhance estrus detection potential due to anticipation by the detector, increased display of estrus due to synchrony of estrus

4. allow scheduling of breeding/inseminations

5. provide synch that is essential to most embryo transfer programs

Name the advantages of Control and Synchronized Estrus (or Timed AI)

Control and Synchronized Estrus (or Timed AI)

What are these advantages of:

1. reduce window of time when insemination is appropriate

2. enhance estrus detection

3. reduce time spent on estrus detection

4. allow scheduling of breeding

5. provide synch for embryo transfer

Shorten luteal phase, lengthen luteal phase (or diestrus)

Overall, what are the principles of control and synchronization of Estrus?

Prostaglandins and Progestin

What two main hormones are used in estrus control/synchronization?

Prostaglandin F2alpha

Lutalyse (Dinoprost tromethamine) and Estrumate (Cloprostenol sodium) are examples of what types of products for Estrus synchronization

Cause luteolysis and regression of corpus luteum (when progesterone is very high) = estrus displayed in 2-5 days

What is the purpose of Prostaglandin F2alpha products like Lutalyse (Dinoprost tromethamine) and Estrumate (Cloprostenol sodium)?

*Only works on days 6-17 of the estrous cycle* = you can't lyse a CL if it's too early and you don't want to do after day 17 because the animals will be coming into estrus anyway

On what days of the estrous cycle can you use Prostaglandin F2alpha products like Lutalyse (Dinoprost tromethamine) and Estrumate (Cloprostenol sodium) and have it be effective?

1. one injection

2. two injections, 11-14 days apart (preferable because the cows that didn't response to the first dose will likely response to the second)

3. heat detect THEN prostagladin F2alpha

What are the common ways to administer prostaglandin F2alpha?

Progestagens

Melengestrol acetate (MGA) and Controlled Intravaginal Drug-Release (CIDR) are examples of what types of products for Estrus synchronization?

You give progesterone for 14 days then pull it away. Their body will move to an infertile estrus for another 16-18 days even tho technically the main circulating hormone is still progesterone. At this point give PGF2alpha to lyse CL and trigger estrus in 2-5 days

Why do you give Progesterone like Melengesterol Acetate in the feed for 14 days? What is the point?

Extend luteal phase and suppress gonadotropin release (FSH and LH)

What is the purpose of Progestagens like Melengestrol acetate (MGA) and Controlled Intravaginal Drug-Release (CIDR)?

Fertility is poor at time of initial estrus (because remember the first estrus after MGA withdrawal is "infertile estrus"), but synchrony is maintained through one cycle

What is the problem with the progestagen Melengestrol acetate (MGA)?

a term for a group of steroid hormones that act like progesterone

Melengestrol acetate (MGA) and Controlled Intravaginal Drug Release are examples of Proestagens. But what IS a proestagen?

Do not breed heifer after withdrawal of MGA

-Feed MGA for 14 days, withdrawl feed for 16-18 days (this is the infertile estrus stage), THEN inject PGF2alpha, and after 5 days the cow will be in estrus

What do you have to keep in mind for animals on Melengestrol Acetate (MGA), a proestagen?

the fertilized eggs enter the uterus prematurely, and the uterine lining is not yet ready for implantation

MGA has an "infertile estrus stage" where you don't breed heifers on the first heat after withdrawal of MGA. Why?

Implant at day 0, remove implant at day 7 and inject with PGF2alpha, then observe for estrus in the next few days and inseminate 12 hours after onset of estrus

Describe the time line for the CIDR program of estrus synchronization using progestagens

GnRH --> causes release of FSH and LH

What hormones are used for Follicular synchronization?

FSH

Which follicular synchronization hormone causes synchronous emergence of a new follicular wave?

LH

Which follicular synchronization hormone causes ovulation?

Estrus synchronization focuses on manipulating the estrous cycle to induce females to exhibit signs of heat (estrus) at the same time. Estrus synch works with progesterone and PGF2alpha.

Follicular synchronization specifically manipulates the growth and development of follicles on the ovaries (multiple follicles at the same time), often in preparation for estrus synchronization or other reproductive procedures. Follicular synch works with FSH, GnRH, and LH.

What is the difference between estrus synchronization and follicular synchronization? How are they related?

Induce a synchronous emergence of a new follicular wave with GnRH

What is the goal of follicular synchronization?

All cows undergo Timed Insemination (TAI)

What follows follicular synchronization? What do all cows undergo?

OvSynch

With this follicular synchronization protocol, you inject GnRH to trigger LH and FSH to grow follicles. One follicle grows dominant and ovulates. Then a CL is formed so you have to give PGF2alpha to lyse the CL. Give GnRH again to ovulate and inseminate.

*note: you give GnRH the first time because they're all at different places in their cycle so you need to lyse them and give GnRH a second time so they're all officially synched up