[Variations of plasma levels of testosterone and delta 4-androstenedione in growing Hubbard cockerels].

Variations in the plasma concentrations of testosterone (T) and delta 4-androstenedione (delta 4) levels were measured by radioimmunoassay in individual young Hubbard Chickens from the age of 16 days until 100 days. Plasma testosterone was low and remained relatively stable between days 16 and 63 (0.10 to 0.30 ng/ml), but increased then rapidly (0.32 +/- 0.07 ng/ml on day 65 vs. 1.49 +/- 0.27 ng/ml on day 100). During the same period delta 4 levels increased too (0.23 +/- 0.06 ng/ml on day 65 vs. 0.75 +/- 0.18 ng/ml on day 100). During the first weeks of life, delta 4-androstenedione prevailed over testosterone. The [delta 4]/[T] ratio reached a maximum between days 30 and 40 and was then reversed to negative values. Results are discussed in relation to those obtained for Chicken from other stocks.