The objective of this work was to study the effects of the injection of 10 mug buserelin (GnRH) in the presence of an ovarian follicle with ³ 10 mm diameter associated to a dose of 500 mug of cloprostenol six days later, or with two doses of 500 mug of cloprostenol (PGF2alpha) at the 12th and 26th days postpartum about the follicular dynamic and the reestablishment of cyclic ovarian activity in crossbred Holstein-Zebu cows. Fifteen crossbred Holstein-Zebu cows were randomly and evenly allocated into three treatments. Ultrasonography was performed every other day from the 14th to the 26th day postpartum and every day, from 26th day until the end of the second estrous cycle. Blood samples were collected twice a week, in order to determine progesterone concentrations by radioimmuno assay. It was observed a pattern of two follicular growth waves during the second postpartum estrous cycles, independent of the hormonal treatment, with the emergence of the first and the second waves, at days 0 and 10, respectively. The dominant follicle from the first wave could persist throughout the interovulatory period without an effect on the follicular dynamic. The two doses of PGF2alpha reduced days open by 20 days and the conception rate at the first service was slightly improved, suggesting a possible effect of the treatment on the hypothalamic-pituitary-ovarian axis.
follicular dynamic; GnRH; postpartum cows; prostaglandin F2alpha
