Pregnancy rate following GnRH + PGF 2α treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment

Abstract

Anestrous and lactating Bos taurus by Bos indicus crossbred cows with minimum body condition were studied to determine the efficacy of GnRH + PGF 2α combinations for induction of estrus and/or ovulation on pregnancy rate during the months of the year when temperatures are greater. On day 0 (start of treatment), cows were assigned randomly to either treatment or control groups. Treated cows ( n = 74) received i.m. 200 μg of GnRH on day 0 and 150 μg of PGF 2α 7 days later (day 7). On day 7, treated cows were equally distributed to each of three protocols: (1) Select Synch ( n = 25), artificial insemination (AI) 12 h after exhibiting estrus from day 7 (PGF 2α injection) until day 12; (2) Ovsynch ( n = 24), 200 μg of GnRH at 48 h after PGF 2α (day 9) + timed-AI (TAI) 16–20 h later; (3) CO-Synch ( n = 25), 200 μg of GnRH + TAI at 48 h after PGF 2α (day 9). Control cows ( n = 25) received no treatment + AI 12 h after exhibiting estrus from days 0 to 12. Detection of estrus was performed daily during the early morning and evening hours from days 0 to 7 in all the cows, and from days 7 to 12 in the cows treated with Select Synch and in the control group, with the aid of a sterilized bull. Palpation per rectum and transrectal ultrasonography were used on days −30, −20, −10 and 0 to confirm anestrus (absence of CL and no signs of estrus at each evaluation) but with ovarian follicles ≥10 mm on day 0. Pregnancy rate was 0% for Select Synch, 21% for Ovsynch and 28% for CO-Synch ( P < 0.05). In conclusion, the Ovsynch and CO-Synch protocols resulted in greater pregnancy rates compared with the Select Synch protocol in Bos taurus/ Bos indicus cows with minimum body condition that were anestrous and lactating during the summer months in a tropical environment.