Effects of chronic and repeated corticosterone administration in rearing chickens on physiology, the onset of lay and egg production of hens.

A corticosterone model was used to study the effects of chronic and repeated stress during the rearing phase on physiology, the onset of lay and performance of laying hens in the subsequent laying period. Two hundred and seventy Hy-line brown layer pullets were reared in environmentally controlled battery cages. At 7, 11, and 15 weeks of age birds were exposed for 1 week to the following treatments in drinking water: corticosterone dissolved in ethanol, ethanol, or untreated water. One week following each treatment, and at 35 weeks of age endocrine, metabolic and haematological tests were conducted. Body weight was measured throughout the study, and egg production was recorded daily throughout the laying period. Plasma corticosterone levels and heterophil to lymphocyte (H/L) ratio were increased after each corticosterone delivery, showing the effectiveness of the treatment. When corticosterone delivery was interrupted, plasma corticosterone and H/L ratio were significantly reduced. Exposing birds to repeated and long-term corticosterone treatment significantly affected BW (P<0.01), and relative organ weights (P<0.01). Corticosterone delivery also resulted in increased blood levels of glucose (GLU), cholesterol (CHOL), and triglyceride (TRG). Administration of corticosterone during the rearing phase delayed the onset of lay and decreased egg production at 35 weeks of age. These results demonstrate that oral corticosterone treatment affects hen physiology, reduces performance, and may model the effects of production stressors.