Physio Review of Bovine Estrous Cycle and Synchronization

Lecture 4

List the phases of the estrous cycle in the cow.

estrus (day 0)

metestrus (days 1-4)

diestrus (days 4-18)

proestrus (day 19-behavioral estrus)

What stage of estrous is described:

• sexual receptivity of the female

• follicular maturation

• peak estradiol levels

• clear vaginal mucus discharge

• uterus toned/firm

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

estrus

What stage of estrous is described:

• final follicular maturation

• ovulation

• formation of early CL — progesterone secretion

• bleeding off of 1-3 days after estrus (not always)

metestrus

What stage of estrous is described:

• period of CL dominance through luteolysis

• uterus not toned (flaccid)

diestrus

What stage of estrous is described:

• progesterone levels decreasing

• estradiol levels increasing

• may see mounters

proestrus

Describe the hormonal profile leading to luteolysis.

progesterone decreases

GnRH increases

LH pulse frequency

Describe the hormonal profile leading to ovulation.

estrogen increasing

estrus signs and pre-ovulation GnRH surge

LH surge

Describe the hormonal profile during diestrus.

progesterone high

estrogen low

LH low

FSH low

Describe the hormonal profile during proestrus.

estrogen increasing

LH increasing

FSH increasing

progesterone decreasing

Describe the hormonal profile during estrus.

estrogen high and peaks

LH surge

FSH peaks

low progesterone

Describe the hormonal profile during metestrus.

progesterone increasing

low estrogen

low LH

low FSH

What two stages of estrous make up the follicular phase?

proestrus

estrus

When does the first follicular wave occur?

either as progesterone is rising or during peak progesterone secretion during metestrus

these will become atretic

When does the second follicular wave occur for cows that have three follicular waves?

peak progesterone secretionduring diestrus

these will become atretic

When does the third follicular wave occur (this may also be the second follicular wave for those cows that only have two waves)?

initiated before luteolysis during proestrus and results in a dominant follcile that will ovulate during estrus

What factors influence puberty of heifers?

genotype

body weight

nutrition

When do we generally see puberty in heifers?

50-65% of her adult body weight

beef: 600-650 pounds (9-12 months of age)

dairy: 700-750 pounds (10-15 months of age)

Cattle under what type of estrous cycle?

non seasonal polyestrus

How long is the bovine estrous cycle?

17-24 days

What is the formula for pregnancy rate?

PR = estrus detection rate (EDR) x conception rate (CR)

Describe management strategy for beef herd breeding.

most bull bred

desire light calcing intervals to maximize grasses, forages, and favorable environmental conditions

AI on certain farms depending on estrus detection

Describe management strategy for dairy herd breeding.

most practice AI

not many bulls

year round calving

follow AM-PM rule for breeding based on estrus detection

Heifers are bred at what age?

14-15 months of age

Heifers calve at what age (assume they were bred at 14-15 months)?

22-24 months of age

What is the voluntary waiting period in dairy cattle?

time period after calving in which cow will not be bred

length determine by physiology, economics, producers, etc

typically 45-65 days

What is termed the period of time from calving to first breeding?

days to first service

Days to first service gives a picture of what?

heat detection or of anestrus

What should the herd average be for days to first service?

75 days (longer is indicative of animals not cycling or not being detected cycling)

What should the conception rate on the first service be?

40% or greater

Why might service rates in dairy cattle be poor?

inadequate estrus detection

poor expression of estrus (heat stress, concrete, feet and legs)

high number of anovulatory cows during early lactation

Why might conception rates in dairy cattle be 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

A cow milking 60 pounds a day has an average time of ____ in standing heat.

14.7 hours

(decreases as milk production increases)

List ways to enhance estrus detection.

proper cow ID

separate into and observe small groups for heat

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

List examples of estrus detection aids.

tail head pressure monitors (tail paint, chalk)

estrus detector animals (chin ball markers, teaser bulls)

pedometry

How can we improve service rate?

estrus control or synchronization such as OvSynch and CIDR Synch (Timed AI)

What term implies that the estrous cycle is exercised such that the onset of estrus may be hastened or delayed?

control

What term implies the coordinated control of estrus in multiple animals?

synchronization

List advantages of control and synchronization of estrus.

reduce the window of time when insemination is appropriate

reduce the time spent on estrus detection

enahnce estrus detection potential due to anticipation by the detector or increased display of estrus due to synchrony of estrus

allow scheduling of breeding/inseminations

provide for synchrony essential to most embryo transfer programs

What are the two general principles for control and synchronization of estrus?

shorten the luteal phase

lengthen the luteal phase

List options for estrus synchronization methods.

prostaglandin programs

progestin programs

luteal and follicular synchronization programs

What estrus synchronization method can be used days 6-17 of the estrous cycle to cause repression of the corpus luteum and display estrus in 2-5 days following?

prostaglandin F2alpha products such as lutalyse (dinoprost tromethamine) or estrumate (cloprostenol sodium)

What estrogen synchronization method can be used to extend the luteeal phase by suppressing gonadotropin release (FSH and LH)?

Progestagens (melengestrol acetate or CIDR)

What can be used for follicular synchronization?

GnRH —> causes release of FSH and LH

gonadorelin diacetate tetrahydrate (Cystorlin)

What is follicular synchronization?

inducing a spontaneous emergence of a new follicular wave with GnRH

List examples of follicular/ovulation synchronization protocols.

OvSynch

Co-Synch

Pre-Synch+OvSynch

CIDR-Synch

Cows on a follicular synchronization protocol undergo what for breeding?

timed insemination (TAI)

What is the difference between estrus synchronization and follicular synchronization?

estrus synchronization extends the luteal phase by suppressing gonadotropin release (FSH and LH)

follicular synchronization induces a synchronous emergence of a new follicular wave with GnRH to cause the release of FSH and LH

What are the two main hormones used in estrus control?

prostaglandins and progestagens typically paired with GnRH

Describe the physiologic actions of GnRH.

causes release of FSH and LH