A $4.7 million grant from the US Department of Agriculture's Agriculture and Food Research Initiative (AFRI) is funding the five-year project. Carl Schmidt, associate professor at the University of Delaware, leads the study with scientists from Iowa State, North Carolina State University, the University of Liverpool and Hy-Line International, the largest breeder of egg-laying chickens in the nation, based in Iowa.

Susan Lamont (Charles F. Curtiss Distinguished Professor in Agriculture), Max Rothschild (Charles F. Curtiss Distinguished Professor in Agriculture and the M.E. Ensminger International Chair) and Michael Persia (assistant professor) are the animal scientists at Iowa State involved in the study.

Iowa leads the nation in the number of laying hens. The combination of high temperatures and humidity occurs regularly in the state causing heat stress, which is also a problem in other areas around the world where chicken production is increasing, Dr Lamont said.

She said: "Most animals used for food production are really performing at a very high level. They're pushed pretty hard in regards to their physiological performance, so if a different stress is added to them it will be an issue for their health as well as productivity."

Using lines of chickens from Iowa State's poultry genetics programme, the scientists will produce experimental populations of chickens and monitor their performance under controlled heat stress conditions. The researchers will investigate the effect of genetics to determine the birds' physiological response to heat stress at different ages.

In cooperation with Hy-Line scientists, the project will assess commercial hens' physiological responses to heat stress, including feed efficiency, egg production and egg quality. The researchers also will work with the University of Liverpool to investigate diverse kinds of chickens native to Africa for genetic signatures that may be related to their reactions to heat.

Dr Lamont added: "We'll see what we can learn from biodiversity, looking at commercial birds and those that have not had a history of genetic selection for food production that may be more tolerant to heat stress."

Work at the University of Delaware will focus on broiler chickens that are raised for meat. North Carolina State researchers will examine the role of epigenetics, a relatively new field that studies genetic impact that is the result of conditioning of the parents. Together, these studies will give a comprehensive picture of the role genes play in the chicken's response to heat stress.