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Seasonal Changes in Serum Testosterone in Adult Rams¹

The Ohio State University and Ohio Agricultural Research and Development Center, Columbus 43210

Abstract

Monthly blood samples collected from seven rams were assayed for serum testosterone concentrations. Testosterone concentrations were lowest in December (.76 ng testosterone/ml serum), increased gradually through April (3.88 ng/ml), and reached 7.42 ng/ml in May. After a transient decrease in June (to 4.15 ng/ml), testosterone concentrations reached a peak of 8.31 ng/ml in July; concentrations then decreased in August and September.

It is suggested that light is the major stimulus to testicular steroidogenesis where summer temperatures are moderate; in hotter climates or during acute temperature increases, thermal factors may override photoperiodic effects.

¹ Journal Article No. 3–75, Ohio Agricultural Research and Development Center. A contribution from the Department of Dairy Science and the Animal Reproduction Teaching and Research Center. The authors are indebted to Dr. J. K. Judy and Mr. R. F. Guenther for providing the animals used in this study, and to Dr. S. A. Tillson, Alza Corporation, for his generous gift of the antiserum used.