Plasma testosterone levels in intact and hemicastrated growing cockerels.

Changes in the levels of testosterone in plasma were measured by radioimmunoassay in blood samples taken at frequent intervals between 2 and 26 weeks of age from entire cockerels and cockerels hemicastrated before 2 weeks of age. In both groups the pattern of testosterone secretion could be divided into three clearly defined phases. In young birds, the levels of testosterone in plasma were low (0.3 ng/ml) but in the prepubertal period, at 11 weeks of age, they started to rise and continued to rise until 22 weeks of age when adult levels, which fluctuated between 2.5 and 3.5 ng/ml, were reached. In the immediate period after hemicastration, the concentration of testosterone decreased temporarily. From 11 weeks of age the levels of testosterone in the hemicastrated birds were approximately 75% of those in intact birds. These results are discussed in relation to the compensatory testicular hypertrophy which occurs in growing cockerels hemicastrated at an early age.