119 Effect of GnRH treatment at the time of embryo transfer on pregnancy rate and embryo/fetal losses in recipient cows

The aim of this study was to evaluate the effect of GnRH treatment at the time of embryo transfer on pregnancy rates and late embryo/early fetal losses in recipient cows. A total of 527 cycling beef cows with a body condition score of 2.5 to 3.5 (1–5 scale) were synchronized as follows: on Day −9, a progesterone device containing 600 mg of progesterone (Diprogest, Zoovet/Ceva) was inserted, and cows also received 2 mg estradiol benzoate (Zoovet/Ceva) intramuscularly (i.m.). On Day −3, the device was removed, and cows received 150 µg of d-cloprostenol (Ciclar, Zoovet/Ceva) and 140 IU recombinant eCG (FoliRec, Zoovet/Ceva) i.m., followed by tail-head painting. On Day 0, cows with more than 50% of their tail-paint removed were considered in estrus, and those with 30%–50% of their tail-paint removed received 10 µg of buserelin (GnRH, Zoovet/Ceva). On Day 7, all cows with >30% of their paint removed on Day 0 and with a CL > 16 mm in diameter (determined by ultrasonography) received grade 1 in vivo-derived frozen/thawed embryos that were collected from 93 donors. Recipients with a follicle > 10 mm in diameter at the time of embryo transfer were randomly assigned to two groups: untreated control (n = 213) and GnRH (10 µg buserelin; n = 314). GnRH-treated cows were further subdivided into ipsilateral (n = 208) and contralateral (n = 106) groups based on whether the largest follicle was present on the same (ipsilateral) or opposite (contralateral) ovary relative to the original CL. Pregnancy diagnosis was performed by ultrasonography on Days 30 and 60, and the presence of accessory CL was evaluated. Data were analyzed using GLMM for binary data with the logit link function (Infostat, UNC). Pregnancy rates at 30 and 60 days did not differ (P > 0.79) among groups (46.9% [100/213] and 41.8% [89/213] vs. 50.0% [104/208] and 43.8% [91/208] vs. 47.2% [50/106] and 40.6% [43/106]) for recipients not treated with GnRH and those treated with GnRH that had the largest follicle on the ovary ipsilateral or contralateral to the original CL, respectively. Furthermore, 30- to 60-day pregnancy losses were 11% (11/100), 12.5% (13/104), and 14% (7/50) for recipients not treated with GnRH and those treated with GnRH that had the largest follicle on the ovary ipsilateral or contralateral to the original CL, respectively (P > 0.85). However, when 30- to 60-day pregnancy losses were analyzed considering the presence of an accessory CL on Day 30 (regardless of treatment group), they were lower (P < 0.04) in recipients with an accessory CL on the ipsilateral ovary (3/67, 4.5%) compared with those without an accessory CL (24/163, 14.7%), and tended to be lower (P = 0.07) than those with an accessory CL on the contralateral ovary (4/24, 16.7%). In conclusion, the data suggest that the use of GnRH at the time of embryo transfer seems to reduce 30- to 60-day pregnancy losses, when the recipient ovulates and forms an accessory CL on the ovary ipsilateral to the original CL.