The relationship between plasma concentrations of progesterone, estradiol and testosterone and the ages of first egg laying in maturing pullets.

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Concentrations of progesterone, estradiol and testosterone in peripheral blood plasma of pullets were measured from 13 to 19 weeks of age, and the relationships between the ages of first egg laying and fluctuations in these peripheral steroids before and after the onset of laying were investigated.1. The average age in days and body weight at the first egg laying were found to be 136.7±0.96 days and 1, 475±13.1g, respectively.2. The egg production rate in the first weeks after the onset of laying showed 61.1%, 73.6%, 75.0% and 81.3% in the group exhibiting the first egg laying at 17, 18, 19 and 20 weeks of age, respectively.3. The concentrations of progesterone in blood plasma were found to remain at a low level (less than 70pg/ml) until 3 weeks before the onset of laying, and then rose sharply 1 to 2 weeks before the onset of laying. In the group exhibiting earlier first egg laying, later increases of concentrations of progesterone was observed.4. The concentrations of estradiol in blood plasma showed a prepubertal peak (more than 320pg/ml) in every group. The earlist and highest observation of this peak was made in the group exhibiting later first egg laying.5. The concentrations of testosterone in blood plasma tended to increase gradually with the onset of laying, and more remarkable changes were observed in the group of later first egg laying.
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