Since LH is luteotrophic in the bovine [22], strategies involving administration of
bovine LH, LH-containing preparations, human chorionic gonadotropin (hCG), or GnRH
have been used to stimulate CL function [23–27]. The ovulation of dominant follicles and
formation of accessory CL increase P4 and reduce estrogen concentrations [28–30]. There
is a paucity of information available on the effect of GnRH administered coincident with
the presence of the dominant follicle of the first (Day 5) and second (Day 15) follicular
wave in cows subjected to synchronization of ovulation and TAI.
The hypothesis of this study was that treatment of cows with GnRH at specific times
after insemination will increase pregnancy rate and reduce pregnancy loss in lactating dairy
cows subjected to synchronization of ovulation and TAI. The objectives of this study were
to compare pregnancy rates (PR) at Days 27 and 55, and pregnancy loss between Day 27
and Day 55 in lactating dairy cows treated with GnRH 5 and (or) 15 days after TAI.