Testosterone propionate effects on gonadotropin secretion in steers after administration of GnRH

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Two experiments with steers were performed to determine the effects of 10 days of treatment with testosterone propionate (TP) on secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) after the administration of gonadotropin releasing hormone (GnRH). In Experiment 1, eight 15-month-old Holstein steers castrated at 12 months of age were used. In Experiment 2, eight beef-type steers between the ages of 12-18 months old and which had been castrated for 8-15 months were used. An initial injection of GnRH was followed by 10 daily injections of TP (175 ug/ kg of body weight) or safflower oil, and on the eleventh day a second injection of GnRH was given. Hormonal endpoints in long-term castrated steers (Experiment 2) were not altered by TP treatment. In contrast, TP treatment significantly suppressed FSH and LH concentrations in daily blood samples from Experiment 1 steers and significantly increased the response to GnRH. The lack of response in the long-term castrated steers (Experiment 2) to TP treatment is similar to the response observed in previous experiments with long-term ovariectomized cows. However, from the results of Experiment 1, it appears that the timing of castration influences the response to TP treatment. © 1984.

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Domestic Animal Endocrinology

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