Abstract
In 86 bulls ranging in age between 3 and 11 months, the maximal plasma testosterone concentration (n = 7) well as the mean concentration (n = 7, same samples) were found to increase with age to peak values at 7–8 months with a subsequent decrease. The multiple correlation coefficient for monthly gain as a function of testosterone concentration and age was 0·85 (P P P r = 0·21). The difference between concentrations of plasma testosterone after stimulation with human chorionic gonadotrophin (HCG) and the spontaneous maximal concentration of this hormone was not significant. High correlation coefficients were found between maximal (r = 0·8) and mean (r = 0·6) concentrations of plasma testosterone before and after an injection of HCG (P <0·001).