Abstract
The aim of this study was to establish which aspect of egg production, plasma lipoproteins and preovulatory follicle steroid hormones in laying hens is altered by thermal environment. In experiment 1, Single Comb White Leghorn hens (80-90wk of age) were exposed to three levels of environmental temperature by rotation (23, 27 and 31°C) for total 3 months, and feed intake, rectal temperature and egg production parameters were measured in each experimental period. In experiment 2, the hens (80wk of age) were exposed to two levels of environmental temperature (23 and 31°C) for 7 days, and concentration of plasma lipoproteins and follicle steroid hormones were determined. Feed intake in hens exposed to 31°C significantly decreased compared with that at 23 and 27°C, and rectal temperature at 31°C was significantly higher than that at 23°C. In the egg production parameter, egg yolk density was significantly smaller at 27 and 31 than at 23°C. Finally, the concentrations of very low density lipoprotein in serum, and of estradiol 17-β and progesterone in follicles were adversely affected by environmental temperature at 31°C. These results suggest that high environmental temperature negatively influences both the lipoprotein and steroid hormones and consequently reduces egg production, but the reduction in feed intake is not the only reason for a decline in egg quality in laying hens.
