Effects of Melengestrol Acetate on Onset of Puberty: DISCUSSION(1)
Administration of MGA to prepubertal heifers for 8 days increased the number of heifers attaining puberty within 10 days after treatment. This effect was associated with an increase in pulsatile LH secretion and growth of the largest ovarian follicle. Our data support the claim that progestin treatment hastens the onset of puberty by enhancing the pulsatile release of LH after the withdrawal of progestin. birth control pills
In our study, 100% of the MGA-treated heifers became pubertal within 10 days after treatment. This response was higher than reported previously in prepubertal heifers treated with MGA or norgestomet. Efficacy of progestins might be dependent on the physiological age of treated animals. Heifers were maintained on a high plane of nutrition and were in excellent body condition at the time of the present experiment. Previous experiences with heifers from the same herd indicates that the heifers were within 1 mo of puberty at the time the present experiment was initiated. In an earlier study, MGA failed to enhance onset of puberty in heifers that were the same age as those used in our current study. However, heifers used in the previous study had slower growth rates and poor body condition before the study was initiated. Hall and coworkers found that the number of heifers exhibiting puberty after norgestomet treatment increased with age. These results suggest that progestin treatment may facilitate onset of puberty but may not initiate the critical events leading to first ovulation. In support of this, Anderson et al. proposed that the ability of progestins to facilitate puberty is related to the maturity of neuroendocrine systems that regulate LH secretion.