Lecture 4: Bovine Estrous Cycle & Synchronization

What is the bovine estrus cycle?

• Estrus = Day 0

• Metestrus = Days 1-4

• Diestrus = Days 4-18

• Proestrus = Day 19-behavioral estrus

What happens during bovine estrus?

• Sexual receptivity of the female - Standing to be mounted is the most definitive sign in cows

• Follicular maturation

• Peak Estradiol levels

• Clear vaginal mucus discharge = bulling

• Uterus toned

• Increased restlessness and bellowing, decreased rumination, appetite, and milk production

What happens during bovine metestrus?

• Final follicular maturation

• Ovulation

• Formation of early CL – progesterone secretion

• Bleeding off of 1-3 days after estrus (not all cows do this)

What happens during bovine diestrus?

• Period of corpus luteum dominance through luteolysis

• Uterus not toned (flaccid)

What happens during bovine proestrus?

• Progesterone levels decreasing

• Estradiol levels increasing - Mounters

Describe progesterone levels throughout the bovine estrus cycle.

diestrus: very high

proestrus: begin to drop until estrus

estrus: extremely low

metestrus: begin to rise again until diestrus

What hormone is inversely related to pregesterone?

estradiol

When does ovulation occur?

At the end of estrus

When does the first follicular wave occur?

either as progesterone is rising or during peak progesterone secretion - follicles selected ruing the first wave will become atretic

When does the second follicular wave occur?

during peak progesterone secretion - follicles selected during second wave will become atretic

When does the third follicular wave occur?

it is initiated before luteolysis and results in a dominant follicle that will ovulate

Which follicles will become eligible for ovulation?

follicles in the growing phase during luteolysis from 2nd or 3rd wave depending on the cow

When do heifers go through puberty?

when the heifer reaches 50-65% of her adult body weight

What is heifer puberty influenced by?

• genotype

• body weight - major factor

• nutrition - underfed = delayed

What is the length for non-seasonal polyestrus of cows vs heifers?

cows: 21 days

heifers: 20 days

How long does estrus usually last (receptivity)?

6-30 hours

When does ovulation occur?

2-20 hours after the end of estrus

How is pregnancy rate determine?

pregnancy rate = estrus detection rate x conception rate

How are beef herds breed?

• most bull bred, but AI on certain farms depending on estrus detection

• desire light calving intervals - maximize grasses, forages, and favorable environmental conditions

How are dairy herds bred?

• mostly AI, not many bulls b/c dangerous

• year round calving

• follow AM-PM rule for breeding based upon estrus detection

What is the voluntary waiting period?

• Time period after calving in which cow will not be bred

• Length determined by physiology, economics, producers, etc

• Typically 45-65 days

What are dairy monitoring parameters used for?

• Used to get a “picture” of the herd’s reproductive history

• Used to identify areas where improvements can be made

• Monitor progress

Once cows are past the voluntary waiting period, cows should be:

• Observed in heat (heat detection efficiency)

• Inseminated

• Conceive

• All should be done in an efficient manner

What is days to first service?

period of time from calving to first breeding

What should the herd average days to first service be?

75 days

What is the reason for days to first service being increased?

either animals are not cycling or not being detected cycling

What is the conception rate on the first service?

should be 40% or greater

If both estrus detection and conception rates are adequate then few cows should have ________.

extended days open

Why is reproductive efficiency in dairy cattle poor right now?

due to low AI service rates and poor conception rates

Why are AI service rates poor right now?

• Inadequate estrus detection

• Poor expression of estrus - Heat, concrete, feet and legs

• High number of anovulatory cows during early lactation - Multifactorial

Why are conception rates currently poor?

• High incidence of EED during early gestation

• Estrus detection errors - Insemination when not in heat

• Semen quality

• AI technique

• Bull fertility

• Milk production and nutrition

• Environmental influences - Temperature

• Age

• Genetics

What is the equation of reproduction?

A x B x C x D = % pregnant

A: herd members detected in heat and inseminated (%)

B: AI technique

C: fertility level of herd (cow)

D: semen fertility level

How can we enhance estrus detection?

• Proper cow ID

• Separate into and observe small groups for heat - Introducing a new animal increases estrus activity

• Ensure proper nutrition

• Provide good footing

• Maintain/assess accurate records

• Train/assign heat detection to one person

• Use estrus synchronization programs

• Use estrus detection aids

What are the possible estrus detection aids?

• tail-head pressure monitors

• estrus detector animals

• pedometry

• vaginal fluid electrical resistance decreases during estrus

What are the advantages to control and synchronization of bovine estrus?

• Reduce the window of time when insemination is appropriate

• Reduce the time spent on estrus detection

• Enhance estrus detection potential due to:

  • Anticipation by the detector

  • Increased display of estrus due to synchrony of estrus

• Allow scheduling of breedings/inseminations

• Provide for synchrony essential to most embryo transfer programs

What are the three estrus synchronization methods?

• Prostaglandin programs

• Progestin programs

• Luteal and follicular synchronization programs

What is the choice of estrus synchronization method based on?

• Cycling vs Not cycling

• Ability to detect estrus

• Facilities and labor to handle cattle

• Drug cost(s)

• Program interval from inception to breeding

How are PGF2alpha products used for estrus synchronization?

causes regression of the corpus luteum → estrus displayed in 2-5 days, but only works days 6-17 of the estrus cycle

How are progestagens used for estrus synchronization?

• extends luteal phase

• suppresses gonadotropin release (FSH and LH)

• feed MGA for 14 days → withdraw feed → after 16-18 days injection of PGF2a → heat detect and AI

• CIDR implant days 0-7 → remove and PGF2a injection → observe for estrus and inseminate 12 hrs after onset of estrus

What is follicular synchronization?

• inducing a synchronous emergence of a new follicular wave with GnRH → all cows undergo time insemination

• GnRH causes release of FSH (synchronous emergence of a new follicular wave) and LH (ovulation)

What is OvSynch?

• an attempt to refine hormonal synchronization for “appointment breeding / timed insemination”

• injection of GnRH → 7 days → injection of PGF → 2 days → injection of GnRH → bred 16 hrs later