Service, conception and pregnancy rates of nelore cows treated with human corionic gonadotropin and estradiol-17² after timed artificial insemination

Abstract

Strategies to reduce embryo mortality in cattle have been evaluated. Nelore (Bos taurus indicus) cows were submitted to timed artificial insemination (TAI D0) after a GnRH/PGF2±/GnRH protocol. Cows were divided in the following groups: Control (Gc; n=55), hCG (GhCG; n=55) received 3000 IU of hCG on D5 , E2 (G E2; n=55) received 5 mg of Estradiol-17² (E2) on D12 and hCG/E2 (GhCG/E2; n=55) received hCG on D5 and E2 on D12. TAI represented the 1st day of a 64 day breeding season. The Ç2 test was applied to compare mating rate (MR), conception rate (CR) and pregnancy rate (PR) to TAI and AIs after natural estrus within the season as well as their accumulated figures at the end of the season. MR and CR for AIs within season did not differ (P>;.10). PR to TAI differed (P<.05) among groups. G E2 showed the lowest rate (5,4%). Gc (34.5%) and GhCG (36.5%) tended (P<.10) to be higher than GhCG/E2 (18.2%). There was no effect of hCG on pregnancy rates. E2 reduced PR to TAI and at the end of season which means that cows receiving E2 (G E2 + GhCG/E2) had lower (66.4%; P<.05) PR than cows not receiving E2 (G C + GhCG; 80.9%). In conlusion, the strategies to manipulate luteal and follicular function herein tested did not increase pregnancy rates in Nelore cows submitted to a TAI.