4. Discussion
In the present experiment, GnRH administration on either Day 5 or Day 15 did not
increase pregnancy rate on Day 27 or Day 55, and did not reduce pregnancy loss between
Day 27 and Day 55. Moreover, administration of GnRH on both Day 5 and Day 15 reduced
pregnancy rate on Day 27 and Day 55.
Previous research showed that administration of GnRH, GnRH agonist or hCG after
insemination at detected estrus and at specific times coincident with the presence of the
dominant follicle/s of the first and second follicular waves may stimulate CL function,
induce accessory CL formation, increase P4 and reduce estrogen production with a
consequent positive effect on embryo survival [39].
Human chorionic gonadotropin administered on Day 7 after insemination induced
accessory CL, increased P4 concentration and reduced embryo mortality compared to cows
treated on Day 0, Day 14, or nontreated controls [28]. A treatment with a GnRH analog
(buserelin, 8 mg) on Day 7 after estrus in postpartum beef cows increased the number of