A Hormone for Hunger in Humans May Leave Chickens Feeling Full

Last year, foreign scientists discovered that while a hormone called ghrelin may boost the appetite of humans, the chicken version of the hormone may have the opposite effect in broiler birds. Now Agricultural Research Service scientists are looking for the genetic components of ghrelin that govern feed intake and calorie expenditure in chickens.

Egg-laying chickens and broiler birds exhibit a significant difference in appetites, with broilers having voracious ones. Animal scientist Mark Richards, of the ARS Growth Biology Laboratory in Beltsville, Md., is looking at the gene for ghrelin in each of these bird types for clues to the difference in appetite. Richards and other scientists have already sequenced portions of the gene that produces the ghrelin hormone, and they are now exploring the genetic differences between the two types of chickens.

Poultry producers have intensively selected for lines of chickens and turkeys that grow faster and produce more meat than previous generations. Unfortunately, along with these improvements have come some unintended changes in feed intake and body composition. Modern commercial strains of broiler chickens tend to overeat when given free access to feed. This can lead to obesity and other health-related problems if the birds are not put on a strict dietary regimen.

Within the central nervous system, specific centers of the brain--the brainstem and the hypothalamus--play critical roles in the regulation of appetite and metabolism. Both food intake and energy balance are biological functions that are orchestrated by intricate biochemical processes involving enzymes, hormones and other types of proteins, each the product of a unique gene.

Scientists do not yet have a complete understanding of the genetic basis for the regulation of these functions in chickens. A better understanding of the genes associated with controlling feed intake and energy balance and how they are regulated by nutritional and hormonal inputs should bring new insights for improving poultry breeding and management practices.

ARS is the U.S. Department of Agriculture's chief scientific research agency.