Induction of ovulation of the first dominant follicle in postpartum beef cows
The objective of this study was to investigate the response of the first dominant follicle postpartum to different treatments to induce ovulation. Twenty-eight cows were submitted to daily ultrasound examination starting at 10 days postpartum. The size and number of follicles present in the ovaries were measured. Upon diagnosis of a dominant follicle the cows were submitted at random to one of the following treatments: GnRH (0.5 mg gonadorelin i. m.); E2 (2 mg estradiol cypionate i.m.); Desmame (temporarily weaned for 48 h); MAP + GnRH (0.5 mg gonadorelin i.m., pre-treated with pessaries impregnated with 250 mg of medroxiprogesterone (MAP) for nine days); MAP+E2 (2 mg estradiol cypionate i. m., pre-treated with the progestagen during nine days); and Control (four cows, untreated). The dominant follicle in the ovaries was detected between 11 and 29 days postpartum. No peculiar effect of treatments on any of the analysed variables was detected. The FD decreased in size by the third day, plasmatic progesterone level increased significantly on Day 6 and ovulation began on Day 2 after the treatment, as indicated by daily ovulation rate. The mean population of follicles detected in the ovaries is about 10, presenting some increase at Days 2 and 3, probably due to the number of small follicles. Irrespective of the small number of cows per group in this study, high ovulation rates (~80%) were observed in groups submitted to the hormonal treatments. The results indicate that the first dominant follicle postpartum responds to hormonal agents with ovulation, which could be used to prime the resumption of normal ovarian function of early postpartum beef cows.
Copyright (c) 1998 Giane Regina Paludo, Jose Ferrugen Moraes, Carlos Jose de Souza, Carlos Miguel Jaume, Cláudio Alvarenga de Oliveira
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