ABSTRACT
Avaliaram-se estratégias para reduzir a mortalidade embrionária em bovinos. Vacas Nelore (Bos taurus indicus) foram inseminadas em tempo fixo (IATF - D0) após o protocolo GnRH/PGF2a/GnRH e divididas nos grupos: Controle (Gc; n=55), hCG (GhCG; n=55) recebeu 3000 UI da hCG no D5 , E2 (GE2; n=55) recebeu 5 mg de 17?-Estradiol (E2) no D12 e hCG/E2 (GhCG/E2; n=55) recebeu 3000 UI da hCG no D5 e 5mg do E2 no D12. A IATF foi o 1o dia da estação de reprodução de 64 dias. Usou-se o teste do c2 para comparar as taxas de serviço (TS), concepção (TC) e prenhez à IATF (TPIATF), às IAs de repasse e acumuladas. A TS e a TC das IAs de repasse não diferiu (P>0,10). Houve diferenças nas TPIATF (P<0,05), pois a TPIATF do GE2 (5,4%) foi a mais baixa e a do Gc (34,5%) e GhCG (36,5%) tenderam (P<0,10) ser maiores que a do GhCG/E2 (18,2%). Não houve efeito da hCG sobre as taxas de prenhez. O E2 reduziu a TPIATF e ao final da estação as vacas que receberam o E2 (GE2 + GhCG/E2) tiveram TPacum (66,4%) mais baixa (P<0,05) de que aquelas (80,9%) que não receberam (GC + GhCG). Em conclusão, as estratégias adotadas de manipulação luteínica ou folicular não aumentaram as taxas de prenhez em vacas Nelore após uma IATF.
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/PGF2a/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 (GE2; n=55) received 5 mg of Estradiol-17b (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 c2 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. GE2 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 (GE2 + GhCG/E2) had lower (66.4%; P<.05) PR than cows not receiving E2 (GC + 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.