ASPECTS OF FOOD-INTAKE RESTRICTION IN YOUNG DOMESTIC-FOWL - METABOLICAND GENETIC CONSIDERATIONS

This paper reviews the literature on the response of young domestic fo wl to various food restriction patterns. Emphasis has been given to an atomical, endocrine and immunological factors and their interactions w ith the genetic background. Under restricted feeding (limitation of th e amount or time of access to food) chickens learn quickly to ingest t he allocated quantity of food within a short period of time. When expo sed to a single sequence of food removal and restoration, body weight losses are reduced for non-adapted compared with adapted individuals, for light breeds compared with heavy breeds, and for older compared wi th younger chickens. Adaptation to food restriction includes increased capacity and slower evacuation of the gastrointestinal tract (mainly the storage organs) to increase the supply of nutrients during the per iods of food deprivation; increased hepatic lipogenesis and glycogen s ynthesis during the feeding cycle; and decreased heat loss on days of food deprivation. Synthesis and secretion of digestive enzymes in resp onse to intermittent feeding has been found to be population dependent and consistent with the hypothesis that the amount of intestinal chym e mediates the synthesis and excretion of digestive enzymes from the p ancreas. Numerous hormones are directly or indirectly involved in the metabolic responses to food restriction. Hyperinsulinaemia, increased plasma levels of growth hormone, triiodothyronine, thyroxine and plasm a prolactin have been observed after the reintroduction of full feedin g. It is suggested that the altered hormonal environment induced by fo od restriction contributes to a metabolic situation that may enhance i mmunocompetence.