Plasma corticosterone concentrations and follicular glucocorticoid receptor mRNA expression in broiler breeder hens as influenced by dietary tryptophan supplementation or feeding program

Abstract

Tryptophan, as a precursor for serotonin, may alleviate behavioral stress when supplemented above the requirement for maintenance, growth and production in chickens. Broiler breeder hens were fed a diet supplemented with 0.05% crystalline tryptophan to determine if it would enhance reproductive performance and reduce stress as indicated by plasma corticosterone levels. At 29 weeks of age, 96 birds were split into 2 groups and placed into individual cages. At 35 weeks of age, one group was maintained on a broiler breeder diet containing 0.20% tryptophan while the other group was fed this diet supplemented with 0.05% tryptophan until 62 weeks of age. Tryptophan supplementation had no effect on egg production, but it decreased plasma corticosterone concentration. In another experiment, plasma corticosterone was measured in broiler breeder pullets fed during rearing either on a skip-a-day or everyday basis until they were 21 weeks of age. All pullets received the same amount of feed over each 48 hour period. At 21 weeks of age pullets were distributed into laying pens and placed on an everyday feeding schedule. At 28 weeks of age follicular mRNA expression of the glucocorticoid receptor was evaluated in the hens. Skip-a-day feeding elevated plasma corticosterone concentrations on the days the birds were not fed. After the hens were all placed on an everyday feeding schedule plasma corticosterone concentrations did not differ between the two groups of hens. However, overall glucocorticoid receptor mRNA expression was lower in hierarchical follicles from skip-a-day hens relative to those that had been fed everyday during rearing. The results indicate that SAD feeding, during rearing, may lead to periods of stress as indicated by plasma corticosterone levels and this may lead to subsequent down-regulation of follicular glucocorticoid receptor mRNA expression. Dietary tryptophan supplementation may alleviate stress associated with restrictive feeding in broiler breeders.