Service, conception and pregnancy rates of nelore cows treated with human corionic gonadotropin and estradiol-17'beta' after timed artificial insemination

Abstract

Avaliaram-se estratégias para reduzir a mortalidade embrionária em bovinos. Vacas Nelore (Bos taurus indicus) foram inseminadas em tempo fixo (IATF - 'D IND. 0') após o protocolo GnRH/'PGF2 IND. a'/GnRH e divididas nos grupos: Controle (Gc; n=55), hCG ('G IND. hCG'; n=55) recebeu 3000 UI da hCG no 'D IND. 5' , 'E IND. 2' ('G IND. E2'; n=55) recebeu 5 mg de '17 IND. b'- Estradiol ('E IND. 2') no 'D IND. 12' e hCG/'E IND. 2' ('G IND. hCG/E2'; n=55) recebeu 3000 UI da hCG no 'D IND. 5' e 5mg do 'E IND. 2' no 'D IND. 12'. A 'IA IND. TF' foi o '1 POT. o' dia da estação de reprodução de 64 dias. Usou-se o teste do 'c POT. 2' para comparar as taxas de serviço (TS), concepção (TC) e prenhez à 'IA IND. TF' ('TP IND. IATF'), às IAs de repasse e acumuladas. A TS e a TC das IAs de repasse não diferiu (P>0,10). Houve diferenças nas 'TP IND. IATF' (P<0,05), pois a 'TP IND. IATF' do 'G IND. E2' (5,4%) foi a mais baixa e a do Gc (34,5%) e 'G IND. hCG' (36,5%) tenderam (P<0,10) ser maiores que a do 'G IND. hCG/E2' (18,2%). Não houve efeito da hCG sobre as taxas de prenhez. O 'E IND. 2' reduziu a 'TP IND. IATF' e ao final da estação as vacas que receberam o 'E IND. 2' ('G IND. E2' + 'G IND. hCG/E2') tiveram 'TP IND. acum' (66,4%) mais baixa (P<0,05) de que aquelas (80,9%) que não receberam ('G IND. C' + 'G IND. hCG'). Em conclusão, as estratégias adotadas de manipulação luteínica ou folicular não aumentaram as taxas de prenhez em vacas Nelore após uma 'IA IND. TF'Strategies to reduce embryo mortality in cattle have been evaluated. Nelore (Bos taurus indicus) cows were submitted to timed artificial insemination (TAI - 'D IND. 0') after a GnRH/'PGF IND. 2a'/GnRH protocol. Cows were divided in the following groups: Control (Gc; n=55), hCG ('G IND. hCG'; n=55) received 3000 IU of hCG on 'D IND. 5' , 'E IND. 2' ('G IND. E2'; n=55) received 5 mg of Estradiol-'17 IND. b' ('E IND. 2') on 'D IND. 12' and hCG/'E IND. 2' ('G IND. hCG/E2'; n=55) received hCG on 'D IND. 5' and 'E IND. 2' on 'D IND. 12'. TAI represented the '1 POT. st' day of a 64 day breeding season. The 'qui POT. 2' 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 'G IND. hCG' (36.5%) tended (P<.10) to be higher than 'G IND. hCG/E2' (18.2%). There was no effect of hCG on pregnancy rates. 'E IND. 2' reduced PR to TAI and at the end of season which means that cows receiving 'E IND. 2' ('G IND. E2' + 'G IND. hCG/E2') had lower (66.4%; P<.05) PR than cows not receiving 'E IND. 2' ('G IND. C' + 'G IND. hCG'; 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 TAIFAPESP 99/03313-9FAPESP 02/08363-