Why Are Chickens Getting So Fat?

In all animals, obesity results from an energy imbalance that occurs when more food energy (calories) is consumed than the body actually needs. The excess energy is stored mostly as fat. Over the years, poultry breeders have bred chickens that grow faster and produce more meat in response to a growing worldwide consumer demand. But modern broiler/breeder chickens don’t adequately balance their feed consumption to match their energy requirements. When these birds are given unrestricted access to feed, they will overeat and become obese.

An important biochemical pathway was discovered in animals that maintains energy balance in the body. A key component of the pathway is an enzyme called “AMP-activated protein kinase” (AMPK), which helps to regulate both energy use by individual cells and food intake by the animal. This pathway is currently being studied in chickens and turkeys.

Animal scientists Monika Proszkowiec-Weglarz and Mark Richards in the ARS Growth Biology Laboratory at Beltsville, Maryland, along with research leader John McMurtry and Penn State University collaborator Ramesh Ramachandran, recently identified and sequenced the genes responsible for the AMPK pathway in birds and showed that they function in different tissues throughout the body of the broiler chicken.

According to Proszkowiec-Weglarz, AMPK plays a central role in sensing cellular energy levels. It begins a series of events that affect food intake and metabolism of fat, carbohydrate, and protein. “AMPK is really a molecular fuel gauge and a master metabolic regulator in cells,” she says. “It responds to fluctuations in the levels of cellular energy and of specific extracellular nutrients and hormones.”

Cells obtain energy from conversion of adenosine triphosphate (ATP) to adenosine monophosphate (AMP). “AMPK senses the ratio of AMP to ATP and works to raise the level of ATP within cells” says Proszkowiec-Weglarz. “Our goal is to learn how the AMPK pathway functions in birds to achieve energy balance, so growers can efficiently produce chickens of optimal weight while minimizing excess fat.”