Abstract
The concentrations of sex steroids in plasma from 2 weeks before the onset to the end of incubation was determined comparing the nesting frequency in Gifujidori hens. The nesting frequency increased progressively from 5 days before the onset of incubation (hen spending more than 90% a day on the nest) and the hens only left less than 2h a day dur-ing the incubation period. Inversely, food and water intake began to decrease from 2 days before the onset of incubation and the mean intake during incubation was 18.8±1.2g of food and 21.9±2.1ml of water. The concentrations of sex steroids began to decrease from 4 days before the onset of incubation reaching basal line levels on the first day in proges-terone, but testosterone and estradiol took an additional one to two days. Significant nega-tive relationships were observed between the nesting frequency and the three sex steriods concentrations. During the incubation, the mean concentrations varied between 55±11 and 103±31pg/ml in progesterone, 60±12 and 124±27pg/ml in testosterone and 29±3 and 55± 16pg/ml in estradiol. The decremental ratio of the plasma concentrations of sex steroids in incubating hens for that of laying hens was progesterone (60%)>estradiol(50%)>testosterone (40%). A significant (p<0.01) relationship with a high correlation coefficient, r=+ 0.648, between progesterone and estradiol was obtained during the incubation period.KONO et al.: Nesting Behavior and Sex Steroid Hormones 71
