Abstract
To examine the effect of GnRH agonist treatment on pregnancy rates in frozen-thawed embryo transfer, 80 Japanese Black beef cattle recipients were divided at random into 2 groups, and the following administration was conducted : The GnRH group (n＝40) underwent intramuscular (i.m.) injection with 100μg of gonadotropin releasing hormone agonist (fertirelin acetate; GnRH-A) on day 6 (day 0 ＝onset of estrus), while the control group (n ＝40) underwent i.m. injection of 2 ml saline as a control. On day 14, the ovaries were examined and the blood concentration of progesterone (P4) was determined in 10 recipients of each group. One newly formed induced corpus luteum (CL) was detected in 90% (9/10) of the GnRH group, while no recipient of the control group had induced CL. There were no significant difference between the GnRH and control groups in P4 concentrations (4.57 ± 1.55 and 3.72 ± 2.39 ng/ml; mean ± SD), or conception rates (50% and 40%). From these results, it is indicated that GnRH-A treatment on the day before embryo transfer have brought new induced CL formation, but have had not increased plasma P4 concentration or the conception rate.
