Changes in plasma concentrations of reproductive steroids in female Japanese quail ( Coturnix coturnix japonica) raised on long or short photoperiods

Plasma concentrations of progesterone, testosterone, estradiol, and estrone were measured by radioimmunoassay in female Japanese quail 22 to 70 days of age. The birds were raised on long (16 hr light per day) or short (8 hr light per day) photoperiods. Only the birds raised on the long photoperiod layed eggs, starting between 42 and 49 days of age. The concentration of each reproductive steroid increased between 28 and 35 days of age, but the increases were more substantial in the birds raised on long days than in the birds raised on short days. Changes in plasma progesterone and testosterone concentrations showed similar trends: the concentrations increased before the onset of lay and were maintained at a high level in the laying birds. In contrast, plasma concentrations of estradiol and estrone increased to a peak at 35–42 days and declined once egg laying became established. The short-day birds also showed increased plasma estrogen levels, maximal at 35–42 days, with estrone being at a higher concentration than estradiol. The increases in plasma steroid levels occurred during the period of rapid growth of the ovaries and oviducts in the long-day birds, although in the short-day birds the growth of these organs was much less substantial.