Seasonal testosterone levels, testosterone clearance, and testicular weights in male domestic cats

Concentrations of plasma testosterone, testosterone clearance rates from plasma, and testicular weights were measured in domestic tomcats during March, June, September, and December. Testicular weights showed a seasonal pattern, with significantly higher values in June than in December and March; however, sperm were present in the seminiferous tubules during all four seasons. The correlation coefficient between seasonal testicular weights and plasma testosterone concentrations was r = 0.929 (P < 0.05). Testosterone clearance rates indicated a half-life of 9.2 ± 2.3 min with no significant differences during the 4 months studied. These data suggest that tomcats are not seasonal breeders, but that there is a positive photoperiodic control of testicular weights. Fluctuations in plasma testosterone concentrations are moderated by testosterone production rather than by changes in testosterone clearance.