Lecture 4: The Estrous Cycle and Synchronization

0. estrus (ovulation)

1. corpus hemorragicum

2. functional CL

3 uterus released PGF2a

4. follicular development in absence of CL

The bovine estrous cycle is 21 days. What are theses major events?

- Estrus = day 0

- Metestrus = day 1-4 = 4 days

- Diestrus = day 4-18 = 14 days (66% of the time)

- Proestrus = day 19-21

How many days are spent in each stage of the bovine estrous cycle?

- Sexual receptivity of the female = stand to be mounted

- increased restlessness/movement, vocalization

- decreased ruminations, appetite, milk production

What are common behaviors seen during bovine estrus?

- Peak estradiol levels

- LH spike

- Peak of FSH

- low progesterone

What hormonally is happening during bovine estrus?

- uterus toned (estrodiol)

- clear vaginal discharge = bulling

What physiologically is seen during bovine estrus?

- toned (like bent forearm)

What does the uterus feel like in a cow during estrus?

- slow increase of progesterone

- low FSH, LH, and E2

What hormonally is seen during bovine metestrus?

- Ovulation

- Formation of early CL

- Final follicular maturation

- bleeding off 1-3 after estrus (not all cows)

What physiologically is seen during bovine metestrus?

- high progesterone

- low FSH, LH, and E2

- GnRH increasing

What hormonally is seen during bovine diestrus?

- CL dominance through luteolysis

- flaccid uterus (progesterone and relaxin) (when you DIE you are flaccid)

What physiologically is seen during bovine diestrus?

- increase in estradiol

- decrease in progesterone

- slow increase in LH + FSH

What hormonally is seen during bovine proestrus?

1. gonadotropic sensitive follicular pool waiting for FSH

2. 1st follicular wave as either progesterone is rising or during its peak secretion. Selected follicle becomes atretic and dies

3. 2nd follicular wave at progesterone peak. Selected follicle becomes atretic and dies (some only have 2 waves)

4. 3rd follicular wave initiated before luteolysis leading to a decrease in progesterone. Selected follicle will ovulate

What are the follicular dynamics like during 1 estrous cycle in the cow?

- when they are 50-65% of their adult body weight

- Beef at 600-650 lbs (9-12 months)

- Dairy at 700-750 lbs (10-15 months)

When do we generally see heifers reach puperty?

- Genotype

- Body weight (major factor)

- Nutrition

What factors influence when puberty is reached in cattle?

- it will delay it

How does being underfed impact puberty?

a. sooner

b. later

How does each of the following impact puberity?

a. cross-breeds

b. inbred

- most bull bred

- desire light calving intervals

What is breeding like in most beef herds?

- most practice AI (not many bulls around)

- year round calving

- often follow an AM-PM rule for breeding

What is breed like in most dairy herds?

- having effective heat detection

What is most important when trying to breed cattle?

- bred at 14-18 months

- calves at 22-24 months

- enters milking herd

When are dairy heifers first breed and when do they first calve?

- the time period after calving where the cow is not bred

- gives the uterus time to return to normal

- length is determined by physiology, economics, producers, ect

What is a voluntary waiting period (VWP)?

- 45-65 days (60 most commonly)

What is the average length of the voluntary waiting period in cattle?

- a observed heat

- inseminated

- conceive

Once cows are past the voluntary waiting period, what should occur?

- once a heat is detected and the animal is bred after the VWP

What does first service mean?

- period of time from calving to first breeding

- herd average should be 75 days

- gives a picture of heat detection or anestrus

What does days to service mean in cattle? What is it like?

- heats not being caught

- animal is not cycling

What are things that can increase days to service?

- 40% or greater

What should the first service conception rate percentage be in a cattle herd?

- inadequate estrus detection

- poor expression of estrus

- high number of anovulatory cows during early lactation

- heat stress

Reproductive efficiency in dairy is poor due to low AI service rates and poor conception rates. What are some reasons for low service rates?

- high incidence of early embryonic death during early gestation

- high estrus detection errors

- poor semen quality

- poor AI technique

- milk production and nutrition

- bull fertility

- environmental influences --> TEMP

- age

- genetics

Reproductive efficiency in dairy is poor due to low AI service rates and poor conception rates. What are some reasons for low conception rates?

- want it to be less than 2.5 in preg cows

- the higher it is the more services they needed to get preg

What is service per conception average of a herd?

true

True or false

as milk production increases the longer time between calving and more services are needed

- 14.7 hours

- heats are very hard to detect

In research, it was shown that the duration of estrus and standing heat for a cow milking 60 lbs a day was on average was _______. What does this mean?

- Proper cow ID

- Separate into and observe small groups

- Ensure proper nutrition

- Provide good footing

- Maintain/assess accurate records

- Train/assign heat detection to one person

- Use estrus synch programs

- Use estrus detection aids

What are management methods to enhance estrus detection on farms?

- Tail-head pressure monitors = chalk, heat watch, kymra

- Estrus detector animals = chin ball markers, gomer/teaser bulls, androgenized heifer/steer

- Pedometry

- Vaginal fluid electrical resistance decreasing detection monitor (Not practical yet)

What are methods used to aid in estrus detection?

- using estrus control or synchronization (OvSynch or CIDR Synch) since they are timed AI protocols

(does not improve inherit fertility of estrus)

What are methods that can be used to improve service rate in cattle?

- control of the estrous cycle that can be used to hasten or delay the onset of estrus

What does estrus control mean?

- implies the coordinated control of estrus in multiple animals

What does estrus synchronization mean?

- Reduces the window of time when insemination is appropriate

- Reduces time spent on estrus detection

- Enhances estrus detection potential

- Allows scheduling of breeding's/inseminations

- Provides synchrony essential for most embryo transfer programs

What are the advantages to a controlled and synchronized?

- Prostaglandin programs = lutalyse or estrumate --> regression of the CL --> estrus in 2-5 days

- Progestin programs = melengestrol acetate or Controlled Intravaginal Drug-Release (CDIR)

What are 2 methods of estrus control and synchronization?

- only from days 6-17

When do are you able to do a prostaglandin protocol?

- lutalyse or estrumate

- regression of the CL --> estrus in 2-5 days

What are the drugs used for the prostaglandin protocol? What are you trying to make happen?

- One injection of PGF2a = 65% response rate

- Two injections of PGF2a = most animals will respond

What are the 2 methods for a prostaglandin protocol?

· First injection --> wait 11-14 days --> second injection --> 2-4 days in estrus

How does the 2 injection prostaglandin method work?

- melengestrol acetate (MGA) or Controlled Intravaginal Drug-Release (CDIR)

- extend the luteal phase and suppress gonadotropin (FSH/LH) release

What are the drugs used for the progestin protocol? What are you trying to make happen?

- feed for 14 days and then withdraw feed --> 16-18 days look for infertile estrus --> PGF2a injection --> wait for heat and AI

How does Melengestrol acetate (MGA) work?

- Placed at day 0 --> wait 7 days --> remove CDIR + PGF2a injection --> estrus in 3-4 days --> AI within 12 hours

How does Controlled Intravaginal Drug-Release (CDIR) work?

- ECS = get animal into estrus during a window

- FS = get all cows to have a synchronous emergence of a new follicular so they can all be bred on the same day. Do not have to do estrus detection because TAI protocol

How does follicular synchronization and estrus control and synchronization differ?

- GnRH / gonadorelin diacetate tetrahydrate

- release of FSH and LH for a synchronous new follicular wave and ovulation

What are the drugs used for follicular synchronization (initiate a new wave of follicles)? What is their purpose?

1. GnRH at day 0 (ovulate those close and produce CL)

2. day 1-7 wait

3. PGF2a at day 7 to rid CL

4. wait 2 days for luteolysis

5. GnRH again at day 9 (mass ovulation)

6. LH surge and ovulation --> day 10 inseminate

What does a typical OvSynch protocol look like?