Journal of Animal Science, Vol 79, Issue 4 1003-1010, Copyright © 2001 by American Society of Animal Science

JOURNAL ARTICLE

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

P. A. Sinclair, E. J. Squires, J. I. Raeside, J. H. Britt and V. G. Hedgpeth
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.

Three studies examined the effects of early postnatal treatment with a GnRH agonist on plasma concentrations of testosterone, dehydroepian-drosterone sulfate, 16-androstene steroids in fat and salivary glands, androstenone in fat and plasma, and testicular development of intact male pigs. The first study involved 45 7-d-old pigs assigned to three treatment groups: 1) boars administered 100 microg/kg of Lupron depot, 2) boars administered 200 microg/kg of 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 microL of 0.5 mg/mL Lupron from d 7 to 35 and controls treated with saline. 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 one of two treatments: 1) boars injected with 200 microL of 0.5 mg/mL of Lupron from d 3 to 35 and 2) control boars injected with saline. Testicular steroid hormone concentrations in plasma decreased (P < 0.01) within 7 d of GnRH agonist treatment. Following cessation of treatment, steroid levels increased to control levels and remained constant until the final rise at 5 mo. Plasma testosterone levels in the 100 microg/kg depot treatment group were higher (P < 0.05) than that of the 200 microg/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 differences (P > 0.05) in concentrations of 16-androstene steroids in salivary glands 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 microg/g and 4.2 microg/g at 7 to 28 d of age. Treatment with GnRH agonist decreased plasma steroid levels and testicular development; however, by d 60 testicular 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 steroidogenesis only during treatment, but testis growth and steroidogenesis had returned to control levels by 60 d of age in male pigs. Suppression of the early postnatal rise in testicular steroid hormones did not affect growth performance or steroid hormone levels at 5 to 6 mo of age.

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