Peripheral plasma androstenedione and testosterone concentrations in bulls before and during puberty

Peripheral plasma samples were collected from 37 young bulls every other month from 2 to 12 months of age. Androstenedione and testosterone were measured by radioimmunoassays. Androstenedione values increased from 2 to 4 months of age (525 +/- 296 (s.d.) pg/ml) and then decreased. Testosterone concentrations increased regularly from 2 months (0.17 +/- 0.14 ng/ml) to 6 months (2.79 +/- 1.29 ng/ml) and then remained at levels around 3 ng/ml. Coefficients of correlation between the hormone concentrations were significant only at 6 months and thereafter.