Resumo

RODRIGUEZ CASTANEDA, Oscar Armando et al. Conception rate at first service in Holstein cows treated with bovine somatotrophin at the time of insemination. Vet. Méx [online]. 2009, vol.40, n.1, pp.1-7. ISSN 0301-5092.

A single dose of bovine somatotrophin (bST) given at the time of insemination improves conception rate (CR) in repeat-breeding cows, but there is no clear evidence that this treatment is useful in first service cows. The effect of bST applied at the time of insemination on conception rate in first service Holstein cows was evaluated. This study was conducted using 435 lactating Holstein cows from 15 dairy herds located in Tizayuca, Hidalgo. Cows were divided in two groups. The bST group (n = 185) received a subcutaneous injection of 500 mg of bST; the control group (n = 250) received 2 mL of saline solution. Insulin growth factor type I (IGF-I) and insulin concentrations were measured daily on seven randomly chosen cows of each group from the day of the bST injection until day 14 post treatment. Pregnancy diagnosis was performed by rectal palpation 45 days after insemination. The effects of treatment, herd, synchronized method (spontaneous or synchronized estrus with prostaglandin F2α), parity and days in milk on conception rate were analyzed by logistic regression for binary variables. The concentrations of IGF-I and insulin were compared using ANOVA for repeated measurements. Conception rate did not varied (P > 0.05) between treatment groups [bST (36.2%) vs control (34.8%)]. There were no herd, parity, days in milk or synchronized method effects (P > 0.05) on conception rate. IGF-I and insulin were higher (P < 0.05) in the bST group than in the control group. It is concluded that a 500 mg bST injection at the time of insemination does not improve fertility in first service Holstein cows.

Palavras-chave : bST; fertility; dairy cattle; IGF-I; insulin.