Heifers and cows that exhibit estrus before fixed-time AI have increased concentrations of estradiol and greater conception rates compared with those that do not. Our objective was to determine whether small doses of gonadotropin-releasing hormone following controlled internal drug-release insert removal would affect estradiol concentrations, estrus expression, or pregnancy success. Beef cattle (n = 247) were synchronized using the 7-d CO-Synch+CIDR protocol and assigned to 1 of 3 treatment groups (0 μg,10 μg, or 5 + 5 μg of gonadotropin-releasing hormone). Animals were observed for estrus, blood samples were collected, and animals were bred by appointment. Concentrations of estradiol were influenced by time ( P < 0.0001) but not by treatment ( P = 0.52) or a treatment-by-time interaction ( P = 0.68). Estrus was not influenced by age ( P = 0.36), treatment ( P = 0.92), or a treatment-by-age interaction ( P = 0.58). Conception rates were influenced by estrus ( P < 0.01), treatment ( P = 0.04), and a treatment-by-estrus ( P < 0.01) interaction but were not influenced by age ( P = 0.27), treatment by age ( P = 0.84), or treatment by estrus by age ( P = 0.94). Animals administered 5 + 5 μg had increased conception rates ( P = 0.01; 69 ± 6%) compared with animals administered 10 μg and tended to be increased ( P = 0.11) compared with 0 μg, which did not differ from 10 μg (53 ± 6% vs. 42 ± 8%, respectively). In conclusion, 5 + 5 μg did not affect concentrations of estradiol or estrus expression but did improve conception to AI.
No takes yet. Share an insight, caveat, or question.
Rich et al. (2018) studied this question.
Synapse has enriched 5 related papers. Consider them for comparative context: