Genetic control of food intake in chickens

Genetic selection for body weight in broiler-type chickens has created a highly efficient omnivore capable of attaining a 2.0 kg body weight in 40-42 d of age with an overall feed conversion (feed consumed per unit of body weight) of less than two. The primary correlated response to the huge increases in the growth of chickens over the last 50 years has been increased feed intake. Although there is much independent data regarding the physiological systems controlling feed intake, there is a dearth of information regarding the inheritance of central and peripheral feed intake control mechanisms. Using four lines of chickens from a double selection experiment for exponential growth rate at different ages, we are investigating changes in both peripheral and central feed intake control mechanisms in response to selection. We have observed a genetic basis for neurotransmitter levels in the hatching chick, which seems to be related to selection for body weight. Diallel crossing experiments have demonstrated that catecholamine levels are inherited in a nonadditive manner, as is feed consumption immediately post-hatch, suggesting that sympathetic nervous activity (as defined by catecholamine and metabolite levels) may be involved in the inheritance of early feed intake in chickens. Further, the use of pharmacological substances (such as monosodium glutamate) known to alter food intake in mammals exhibit signs of genotype by treatment interactions for growth and hypothalamic neurotransmitter levels. These data suggest a research strategy to separate genetic changes in food intake from those related to responses in metabolism.