RESUMO
Twenty eight Holstein cows [16 heifers and 12 multiparous cows] were used. Heifers were weighed 350-380 kg, and failed to conceive till 2.5 years old. Multiparous cows calved since about 5-6 months and showed no any oestrus signs and low plasma progesterone. Heifers were assigned to three treatment groups in a randomized design. Eleven heifers were treated with a single injection per heifer of rb ST [Somatech]. Two days post injection, all heifers were rectally examined to ensure ovarian activity and follicular development. Seven days later, six of these rbST-treated heifers were injected PMSG. Third group were kept as control. Multiparous postpartum cows were assigned to two groups. First group [n=7] received bST, and second one [n=5] were treated with both rbST and PMSG injections according to the same procedure of heifers. Two weeks before treatment, blood samples were collected from all experimental animals once weekly, and then once daily on day 2, 3, 7 and 12 post injection for determinations of IGF-1 and insulin concentrations. Oestrus was detected in heifers and cows by usual observation and progesterone profile. All heifers and cows that detected in oestrus were artificially inseminated. First-service conception rates and pregnancy percentages were obtained. Postpartum cows were milked twice daily and average daily milk production was calculated before and after injection of bST. Plasma concentrations of IGF-1 and insulin showed significant increases in bST-treated heifers. However, IGF-1 concentrations were decreased after bST injection, and plasma insulin concentrations did not significantly affected in postpartum cows. Treatment with bST caused improving of the reproductive performance of heifers and postpartum cows