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No experimento foram utilizados 62 animais da raça Charolesa e Caracú, inseminados artificialmente (IA). No 7o dia após a IA, as vacas foram divididas aleatoriamente em 2 grupos: tratado (n=32), que recebeu 2.500 UI de hCG (IM) e controle (n=30), que recebeu 1 ml de solução fisiológica estéril, (IM). O diagnóstico de prenhez foi realizado por toque retal no 45o dia após a IA. Resultados: A duração do ciclo estral diferiu (P0,05) entre o grupo tratado e controle (40,62% e 23,33%, respectivamente). Conclusões: A duração do ciclo estral dos animais tratados foi prolongada em relação aos controles (P0,05) as taxas de prenhez em bovinos de corte. Effect of human chorionic gonadotropin (hCG) on estrous cycle length and pregnancy rates in cattle Abstract In the present experiment a total of 62 cows of Charoles and Caracú breeds, artificially inseminated (AI). At day 7th after AI the cows were aleatory distributed in two groups: treated group (n=32) that receive 2.500 UI of human chorionic gonadotropin (hCG) by the intramuscular route and control group (n=30) to wich 1.0 ml of sterile physiological solution was administered also by the intramuscular route. It has been found that the estrous cycle lenght was different (P0,05) between treated and the control groups (40,6 and 23,3%, respectively). In this way, the estrous cycle lenght of the treated cows was extended in regard to the control cows. The hCG administration did not increase pregnant rates.

No experimento foram utilizados 62 animais da raca Charolesa e Caracu, e inseminados artificialmente (IA). No 7o dia apos a IA, as vacas foram divididas aleatoriamente em 2 grupos: tratado (n=32), que recebeu 2.500 UI de hormonio corionico gonadotrofico (IM) e controle (n=30), que recebeu 1 ml de solucao fisiologica esteril, (IM). Verificou-se ultrassonograficamente a localizacao e o diâmetro: do corpo luteo do cio base (CLCB) no 7o e 13o dia apos a IA, do foliculo dominante (FD) da primeira onda no 7o dia, do corpo luteo acessorio (CLA), e do FD da segunda onda folicular. Coletaram-se amostras sanguineas no 7o, 13o e 24o dia apos a IA para a determinacao da concentracao de progesterona plasmatica (P4) pelo metodo da quimioluminescencia. Foram obtidos os resultados: Trinta e um animais (96,87%) desenvolveram um CLA apos a aplicacao do hCG. O diâmetro do CLCB e do FD no dia 7 e 13 apos a IA, nao diferiram entre os grupos (P>0,05). A concentracao de P4 no dia 7 nao diferiu (P>0,05) entre os grupos, porem no dia 13 (P Inducion of accessory Corpus luteum by human chorionic gonadotropin (hCG) and the relationship with progesterone concentrations in cattle Abstract In the present experiment 62 cows of the Charoles and Caracu breeds were artificially inseminated (AI) and aleatoryly divided in two groups at the 7th day after the insemination. The experimental group (n = 32) has been tretaed with intramuscular administration of 2500 IU of human chorionic gonadotrophin (hCG) and the control group (n=30) with 1.0 ml of intramuscular sterile physiologic solution. Scanning ultrasound was performed at the 7th and 13th day in order to access the location and size of the estrus corpus luteum (CL), the dominant follicle (DF) of 1st and 2nd follicular wave at 7th and 13th day, respectively, as well as the diameter of accessory CL. Blood samples were collected at 7th, 13th and 24th days after AI for progesterone (p4) assay by chemiluminescent immunoassay. Results. A total of 31 cows (96.8%) developed an accessory CL after hCG administration. No differences has been found (P