Bovine Estrus & Synchronization Flashcards
What kind of cycle do cows have?
nonseasonal polyestrus - cycle all year around
What is the overall length of the bovine estrous cycle? How long are each stage?
21 days (17-24)
- estrus = day 0
- metestrus = day 1-3
- diestrus = day 4-18
- anestrus or proestrus = day 19 until next estrus
What period of estrus is considered the best time for sexual receptivity? What happens at this time?
12-15 hours
standing heat - will remain still and standing while mounted by other cows in proestrus or bulls
What is the onset of bovine estrus to ovulation?
~30 hours —> 12-18 hours following standing heat
(oocytes ready for insemination, if waiting too long the oocyte will likely die)
Why do dairy cattle typically have shorter periods of estrus?
due to their use for their milk, they will have increased blood flow to the liver, where estrogen will be broken down
What is the difference between 2 and 3 wave cycles in bovine estrus?
2 wave = shorter follicular waves/estrus where one dominant follicle regresses over the period of the estrous cycle before another dominant follicle progresses to ovulation in the second wave
3 wave = longer follicular waves/estrus where two waves of dominant follicles regress over the period of the estrous cycle before another dominant follicle progresses to ovulation in the third wave (longer cycle, shorter time between DF emergence and ovulation)
When does proestrus occur during the bovine estrous cycle? What hormone changes occur during this time?
day 19 until estrus
progesterone decreases and FSH/LH increase in response to GnRH, inducing estrogen production by ovarian follicles
When does estrus occur during the bovine estrous cycle? What 3 things are occurring?
day 0 (standing heat!)
- follicle recruitment and selection where a single follicle dominates and produces estrogen and inhibin that decrease FSH and the growth of other follicles
- LH surge causes follicular maturation and ovulation
- follicular cells produce estradiol, which leads to progesterone production
When does metestrus occur during the bovine estrous cycle? What are 3 characteristic changes in hormones?
days 1-3 after ovulation
- low LH
- low estradiol
- rising P4
What is a normal occurrence during metestrus in cows? What triggers it?
hemorrhagic vaginal discharge - sanguineous vaginal discharge 24-48 hr after ovulation from caruncular capillaries (50-60% cows, 75-85% heifers)
estrogen withdrawal common during metestrus
When does diestrus occur during the bovine estrous cycle? What 3 things happen?
days 4-18 following ovulation
- progesterone elevation greater than 1 ng/mL by day 4, peaking at 8-10)
- functional luteolysis 24 hrs after the secretion of uterine (endometrium) PGF2alpha
- entrance into a new follicular phase (proestrus) after luteolysis
What happens histologically during luteolysis?
CL —> corpus albicans (scar tissue) within 48 hr
What are the 3 triggers of waves in the bovine estrous cycle? What causes follicular recruitment?
- dominant follicle removal
- ovulation/GnRH
- estrogens
high FSH (due to GnRH release)
How do follicles appear on ultrasound?
black/anechoic structures = fluid-filled cysts of the follicles
(bouncier compared to stroma on palpation)
Bovine estrous cycle:
What breeding strategy is most commonly used on beef farms?
natural mating —> cows exposed to bull in the pasture and bull breeds whenever cows are receptive
What breeding strategy is most commonly used on dairy farms?
artificial insemination with heat detection using teaser animals and observing for riding cows
How is it determined when to perform artificial insemination? Why?
AM/PM rule —> if head is observed in the AM, breed in the PM and vice versa
optimal fertility of ova is between 6-12 hours after ovulation
What is the viable lifespan of sperm?
24-30 hours (cryo greatly reduces viability)
- AM/PM rule! —> cows’ ova are most receptive 6-12 hours following ovulation
How is artificial insemination performed? What landmark is used? What needs to be avoided?
transrectally
cervix is palpated rectally and fitted over insemination rod, which must bypass 2-3 cervical folds
fornix at the side of the cervix - continued pushing of the rod can cause perforation
How often are cows manually observed for estrus?
one hour in the morning and one hour in the evening
How long does estrus occur? What are 2 differences between species of cows?
12-15 hours
- dairy < beef (milking = increased blood flow through liver)
- Bos indicus < Bos taurus
What are 6 options for estrus detection aids?
- heat mount detectors - pressure from other cows/bulls mounting rubs off silver into red/pink
- paint, chalk, or paste tailhead markers - rubs off when mounted (need to change colors constantly!)
- teaser bulls - deviated penis allows bull to mount without insemination
- vaginal mucus electrical resistance probe
- pedometers - walk around more when in estrus
- Heat Watch
What are the major disadvantages of manual estrus detection?
- time consuming
- labor intensive
- relatively expensive
led to the development of estrus synchronization
What is the goal of estrus synchronization?
synchronize estrus/ovulation to reduce time spent on estrus detection and allow for timed AI
What are the 3 major strategies for synchronization of estrus in cows?
- control length of the luteal phase
- stimulate a new follicular wave
- induce ovulation
What strategies are used to extend and shorten luteal phases?
EXTEND - exogenous progesterone/progestins (CIDR intravaginal insert, melengestrol acetate)
SHORTEN - PGF2alpha
When must PGF2α be given to cows to shorten the luteal phase?
6 days following estrus —> no response any earlier
How can ovulation be induced when synchronizing estrous cycles?
GnRH - induces ovulation of the preovulatory (dominant) follicle
What are 3 steps to the Ovsynch protocol for synchronizing estrous cycles in cows?
- 1st GnRH administration - induces ovulation or luteinization of follicles present
- PGF2α administration - lyses any luteal tissue present
- 2nd GnRH administration - induced ovulation of the preovulatory follicle
What is commonly added to the Ovsynch protocol? Why?
CIDR intravaginal insert (progesterone)
extends luteal phase to induce estrus and ovulation in some non-cycling females
