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Active Immunization of Prepubertal Boars Against Testosterone: Testicular and Endocrine Responses at 14 Months of Age

Louisiana State University Agricultural Center², Baton Rouge 70803

Abstract

Thirteen crossbred boars were immunized at 1 mo of age against either testosterone-3-oxime-equine serum albumin (treated boars) or equine serum albumin (control boars) to test the hypothesis that active immunization against testosterone stimulates testicular growth and development in the prepubertal boar. All boars were injected with the appropriate antigen at 2, 3, 4, 5 and 6 mo of age and were slaughtered at 14 mo of age. Active immunization against testosterone resulted in an increase (P<.05) in tritiated-testosterone binding by plasma within 60 d after the primary immunization; the degree of binding decreased by 6 mo but remained elevated (P<.05) relative to controls through 12 mo of age. There was no effect of treatment on body weights through 12 mo of age. Concentrations of testosterone in plasma were higher (P<.05) in testosterone-immunized boars than in controls; this increase was likely due to antibody binding rather than increased testosterone secretion because (1) concentrations of androgen in testicular parenchyma at slaughter were not altered by treatment and (2) plasma concentrations of estrogens were generally not affected by treatment. Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were markedly suppressed in testosterone-immunized boars during the time when concentrations of these gonadotropins were high in control boars (>3 mo of age). In spite of suppression of average LH and FSH concentrations, testicular weights, daily sperm production rates and seminal characteristics were similar for the two groups of boars at slaughter. It is concluded that the boar differs from the bull in its response to prepubertal active immunization against testosterone in that testicular size and sperm production rates are not altered, although gonadotropin secretion is reduced. Further research is needed to define better the relationships between plasma gonadotropin concentrations and testicular development in the boar.

¹ Address reprint requests to D. L. Thompson, Jr.

² Dept. of Anim. Sci., Louisiana Agr. Exp. Sta.

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