Biology of Reproduction, Vol 22, 765-771, Copyright © 1980 by Society for the Study of Reproduction

Plasma Testosterone Concentrations in Bulls with Intact and Shortened Scrotums during Sexual Maturation

¹ Institut für Zuchtygiene, Universität Zürich, 8057 Zürich, Switzerland

Peripheral plasma testosterone was determined by radioimmunoassay in 6 bulls with intact (I) and 6 bulls with experimentally shortened scrotums (SS) at biweekly intervals from 14 to 36 weeks of age. Blood samples were collected from an indwelling jugular catheter every hour during an 8 h period (0800-1600 h). When the hormonal profiles obtained from both groups during sexual development are compared, three time periods can be distinguished: 1) At 18 weeks of age, onset of testosterone secretion with peak values >1 ng/ml was first seen in I bulls compared with 28 weeks in SS bulls. 2) From 28-32 weeks of age, testosterone showed high fluctuations in I bulls, whereas the 8 h profiles of SS bulls were characterized by low fluctuating values never falling below 1 ng/ml. 3) During the period of 32-36 weeks of age, mean minimum hormone concentrations dropped to <1 ng/ml in SS animals, whereas mean maximum values increased to >6 ng/ml in both experimental groups. Histological examination of SS testes at the age of 15 months revealed atrophy of the seminiferous epithelium with no spermatozoa present. Results from this study indicate that episodic testosterone secretion observed in prepubertal bulls is a maturational process of Leydig cells which was delayed for about 2 months in SS bulls. Elevated gonadal temperature influenced testosterone secretion temporarily and caused striking morphological changes.

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ACKNOWLEDGMENTS The authors express their gratitude for the excellent technical assistance provided by Mrs. S. Pletscher, Mrs. A. Hug and Mr. R. Jörg. We also are indebted to Mrs. E. Straumann for helpful secretarial assistance.