Testosterone concentrations in chicken gonads and plasma during the peri-etching period

In chick embryos of the black sex-link strain, the concentration of testosterone was much lower on Days 17 and 18 of the incubation period in both gonads (tests and left ovary) than on the next two days. Then, at hatch, and especially at 1 h after hatching, the concentration decreased in both gonads. Between 2 and 4 h after hatching, the concentration of T reached the highest value in each sex and then decreased progressively within the next 18 h. Concentrations on Days 19 and 20 (in both gonads) differed significantly from those on Days 17 and 18 of the incubation period, but no significant sex differences were found at these four sampling times. In newly hatched chickens, significant differences were found only between the values obtained at 1 h after hatching (in both sexes) and those from 2-4 h after hatching; no significant sex differences in T concentrations were found in gonads on Day 1 after hatch. The concentration of T in plasma from females was a little higher than in males on Day 19 of incubation, but no significant differences were found. At hatch, the concentrations were of the same order of magnitude in both sexes. At 1 and 2 h after hatching, increased values were found only in males; pooled values of these two sampling times were significantly different from those obtained either in embryos or at two periods after hatching (8-20 h and 48-68 h respectively). No significant changes occurred in T concentration in plasma from females over all these sampling times. By 3-6 h after hatching, the concentrations of T returned to near hatching concentrations in both sexes, and then decreased progressively between 8 and 68 h after hatching. No significant differences in plasma T concentrations were found between males and females, at hatch, or within the next 68 h. In red sex-link strain chickens, the concentrations of T in plasma were about the same in both sexes, at hatch and on Day 1 after hatching, but the concentrations were much lower than those recorded in black sex-link strain chickens at the same sampling times. A peak of T was found only in plasma from newly hatched male chickens of the black sex-link strain at 1-2 h after hatching but not in females, and not in red sex-link strain (of both sexes) either.