The elucidation of regulatory mechanism of food intake in higher animals by the comparison of feeding behavior of broiler- and layer-type chickens.

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Modern broiler-type chickens have been intensively selected for rapid body weight gain and high meat yield, whereas layer-type chickens have been selected for higher egg production. Therfore, genetic selection has introduced wide variations in growth rate between the two strains. The differences in the growth rate could be partly explained by the difference in food intake between the two strains. Research over the past several decades has examined the brain neurochemical systems that regulate food intake in mammalian and avian species, and has identified a number of neurotransmitters that appear to contribute to this behavior. Recently, it has been recognized that regulatory mechanism of food intake in chickens appear similar to that in mammals. Therefore, this study was conducted to elucidation of regulatory mechanism of food intake in higher animals by the comparison of feeding behavior of broiler- and layer-type chickens. First, we investigated the effects of neuropeptide Y, a poten … More t stimulator of food intake, and cocaine- and amphetamine-regulated transcript (CART), a suppressor of food intake, on neonatal broiler- and layer-type chicks and the results indicated that responsiveness to NPY was somewhat different between the two strains. Futehrmore, it was also suggested that CART interacted with NPY in the central nervous system to regulate feeding in chicks. Next, we investigated the differences in hypothalamic catecholamine metabolism and the effects of γ -amino butyric acid (GABA) receptor agonists and antaonists in neonatal broiler- and layer-type chicks and the results indicated that some differences in catecholamine metabolism and in GABAergic systems are present between the two strains. Finally, we investigated the variation of hypothalamic NPY gene expression and peptide content of broiler- and layer-type chickens at neonatal period and the results indicated that the hypothalamic NPY gene expression and peptide content as well as plasma metabolites were changed by feeding conditions. These results suggested that NPY gene expression might be regulated with the blood glucose level and other factors such as leptin might play a role in the regulation of NPY gene expression. As mentioned above, there is the possibility that the differences in the feeding behavior between the two strains is partly due to the differences of responsiveness to NPY, hypoyhalamic cathecholamine metabolism and GABAergic system. Less