Long-term effect of incubation temperatures on production parameters and changes in luteinizing hormone and gonadal steroids during the onset of lay in the hen.
Earlier studies demonstrated that different incubation temperatures (33.8 or 37.8 C) from Day 17 of incubation until hatching resulted in differences in postnatal growth rate and hormonal parameters. These studies were repeated and extended to the reproduction period. The onset of egg laying was significantly delayed by 5 days in the 33.8 C group compared to the 37.8 C group. No differences in percent egg production were found between the groups after 3 or 5 months of production: however, mean egg weight was significantly reduced in the 33.8 C group by 1.9 and 1.8 g over 3 and 5 months of production, respectively. Serum concentrations of luteinizing hormone (LH), estradiol (E2), estrone (E1), progesterone (P4), and testosterone (T) were measured weekly at the same time of day approximately 4 weeks before to 4 weeks after the onset of lay. The changes in levels of all hormones over the period studied were identical for both experimental groups. Luteinizing hormone, T, and E2, but not E1 and P4, were different before and after onset of lay in both groups. There were no significant correlations between hormonal levels before onset of lay and production traits for individual hens. In the 33.8 C group, after onset of lay, significant positive correlations were observed between serum E2 and egg production and serum LH and egg production; however, these correlation coefficients were not significant in the 37.8 C group. Significant negative correlation coefficients were observed in both groups between serum E2 after onset of lay and age at first egg.