The effect of early postnatal treatment with a gonadotropin-releasing hormone agonist on the developmental profiles of testicular steroid hormones inthe intact male pig

Three studies examined the effects of early postnatal treatment with a GnRH agonist on plasma concentrations of testosterone, dehydroepiandrosterone s ulfate, 16-androstene steroids in fat and salivary glands, androstenone in fat and plasma, and testicular development of intact male pigs. The first s tudy involved 45 7-d-old pigs assigned to three treatment groups: 1) boars administered 100 mug/kg of Lupron depot, 2) boars administered 200 mug/kg o f Lupron depot, and 3) control boars receiving a saline carrier. The second study involved 20 7-d-old pigs assigned to two treatments: daily injection of 200 muL of 0.5 mg/mL Lupron from d 7 to 35 and controls treated with sa line. The third study involved a total of 100 animals assigned to 10 groups of 10 based on their age at slaughter. These groups were subdivided into o ne of two treatments: 1) boars injected with 200 muL of 0.5 mg/mL of Lupron from d 3 to 35 and 2) control boars injected with saline. Testicular stero id hormone concentrations in plasma decreased (P < 0.01) within 7 d of GnRH agonist treatment. Following cessation of treatment, steroid levels increa sed to control levels and remained constant until the final rise at 5 mo. P lasma testosterone levels in the 100 <mu>g/kg depot treatment group were hi gher (P < 0.05) than that of the 200 <mu>g/kg and control group at 164 d of age. There were no differences between treatments (P > 0.05) in testicular steroid hormone levels at the end of study 2 or 3. There were no differenc es (P > 0.05) in concentrations of 16-androstene steroids in salivary gland s between any of the treatment groups at market weight in studies 1 and 2. Fat androstenone levels measured in the third study ranged between 0.6 mug/ g and 4.2 mug/g at 7 to 28 d of age. Treatment with GnRH agonist decreased plasma steroid levels and testicular development; however, by d 60 testicul ar size and weight were at control levels and remained similar until 180 d of age. The results of these studies indicate that daily administration of a GnRH agonist significantly decreased testicular development and steroidog enesis only during treatment, but testis growth and steroidogenesis had ret urned to control levels by 60 d of age in male pigs. Suppression of the ear ly postnatal rise in testicular steroid hormones did not affect growth perf ormance or steroid hormone levels at 5 to 6 mo of age.