Manipulation of the Estrous Cycle Flashcards
Synchronization of estrus
Timing the onset of estrus and the events leading to ovulation of fertile oocytes is determined by human actions
A group of females display estrus and ovulate fertile oocytes within a few hours of each other
Purpose of estrous synchronization is to allow group=mating
Hypothalamus
releases small peptides of which GnRH is of direct importance
GnRH causes pituitary release of FSH and LH
Action of GnRH
causes release of Luteinizing Hormone (LH)
Ovulation or luteinization
Initiates new follicular wave
CL formation
Corpus Luteum
progesterone prepares the uterus for the egg (D5)
P4 acts on the prain to override estrogen to prevent estrus behavior
Higher levels of P4 are needed to prevent ovulation than estrus
Action of Progesterone
Secreted by CL
Suppresss estrus and ovulation
Pregnancy maintenance
“jump start” anestrus females
We control the estrous cycle by controlling the progesterone level (CL)
Regu-mate, MGA, and CIDR inserts are commercial examples
Uterus
PGF2a is produced by the non-pregnant endometrium to lyse the CL and initiate the process that leads to ovulation
Some species have a very short time window when PG will lyse the CLs
Alpacas and llamas are very sensitive to PFG2a and have severe reactions (even deaths) - DO NOT use in them
Synchronization of Estrus:
Bovine
Commonly done to enhance the utilization of artificial insemination
Synchronization of cycle:
Bovine:
Progestogens
if treatment is 14 days or less - must combine with a luteolytic agent to successfully control time of estrus
Synchronization of Estrus:
Bovine
Progestogen plus prostaglandin
Prostaglandin F2a and its analogs cause luteolysis and a return to estrus when given during the luteal phase (d5-17)
Fertility of PGF2a - induced estrus is normal
PGF2a is more successful at causing luteolysis when given late (d10-17), versus early (d5-9) in the luteal phase
Synchrony of estrus is tighter when cattle are at a similar stage of the estrous cycle when treated with PGF2a
Normal fertility
Synchronization of Estrus
Bovine
Effect of day of cycle when PG is injected
Synchronization of Estrus:
Ovine
Prostaglandin F2a
Only works in cycling ewes
Give two injections 9 days apart
No percise enough for timed insemination
Synchronization of Estrus
Ovine
Progestrogen alone (or with hCG + eCG)
Progestrone id administered for 12-14 days via CIDR or vaginal pessary
In estrus 36-40h after P4 removal
Timed A.I. 48-52h after P4 removal (fresh semen) or 53-58h after P4 removal (frozen semen)
Can add PG600 at time of P4 removal
Synchronization of Estrus
Procine
The age of puberty in gilts can be reduced slightly with hormonal treatment
Gilts should be within 1 month of natural puberty (6-7 mo of age)
SIngle injection of a combination of eCG and hCG
50-70% of prepubertal gilts will exhibit estrus within 7 days
Will not result in a predictable timing of estrus in gilts that are already cycling
Can inject PGF2a 18 days after PG600 to tighten estrus synchrony of the subsequent cycle
Does NOT work in Cycling Gilts
Because the pig CL is resistant to PGF2a until late in diestrus - this hormone is not very useful in pigs compared to other species
Abortifacient activity of PGF2a - pen mate gilts for 3 weeks and then give PGF2a two weks later
Can feed progestogen for 18-19 days - will return to estrus in 4-5 days.
TIming of estrus in lactating sows is usually controlled by weaning the piglets
Manipulation of Estrus
Equine
Manipulating the onset of estrsu is easier than predicting/synchronizing ovulation
Estrus manipulation/synchronization benefits: efficient use of stallion, ability to schedule breeding, synchronization of recipients of ET
Manipulation of Estrus
Equine
PGF2a
need lower dose than with cattle
CL can be lysed in late estrus and during diestrus
Side effects can be pronounced:
sweating, colic, increased heart rate, weakness and ataxia
2 injections 14 days apart
60% in estrus within 4 days
90% in estrus within 6 days
Ovulation 2-12 days after last injection
