Relationship of intratesticular testosterone content of stallions to age, spermatogenesis, Sertoli cell distribution and germ-Sertoli cell ratios

Abstract

Testes were obtained from 47 1-20-year-old stallions during the natural breeding season. Total testicular testosterone and testosterone/g testis increased with age (P < 0.005), and total testicular testosterone was associated with larger testis size (P < 0.05). Neither testosterone per gram nor per paired testes were related to total Sertoli cell number (P > 0.05), but greater testosterone per paired testes was associated with fewer Sertoli cells per unit of seminiferous tubule length (P < 0.005) or basement membrane area (P < 0.02) and with a higher number of germ cells supported per Sertoli cell (P < 0.05). Although values for testosterone per gram and per paired testes were unrelated (P > 0.10) to sperm production/g testis or to the yield of spermatids/spermatogonium, testosterone per paired testes was positively related to sperm production per paired testes (P < 0.05). It is concluded that intratesticular testosterone increases with age, is related in a positive manner to quantitative rates of sperm production, and can account for some of the differences in sperm production among individual stallions within a single breeding season.