Daily alterations in plasma testosterone in boars at different ages.

Eighteen purebred Yorkshire boars, reared outdoors on concrete, were randomly assigned in equal numbers to three age groups (150+/-7, 200+/-7 and 250+/-7 days of age) for the purpose of examining endogenous testosterone concentrations over a 24-hr period. Blood was obtained at 30-min intervals for 24 hr, and plasma testosterone concentrations were quantitated by radioimmunoassay. For each set of 24-hr samples, mean concentration (C), frequency (F) and magnitude (M) of secretory spikes of testosterone were determined. There was no difference (P>.10) in C, F and M across the three age groups. When averaged over ages, testosterone mean (+/-SEM) for C, F and M was 1.4+/-.1 ng/ml, 2.9+/-.5 and 3.0+/-.3 ng/ml, respectively. The results suggest that testosterone secretory patterns are established in boars by five months of age and that these patterns may be influenced by degree of daylight.