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Pre-Conditioning for Hot Weather May Aid Birds

By Sharon Durham
August 16, 2002

Chicks kept in higher than normal temperatures for the first three days after hatching show improved performance and heat tolerance as well as reduced mortality. These findings are from collaborative research by Agricultural Research Service scientists and Israeli researchers, aimed at reducing problems experienced by commercial producers during heat waves.

In a collaborative study led by ARS scientist John McMurtry of the agency's Growth Biology Laboratory in Beltsville, Md., three-day-old chicks were placed in 100 degree Fahrenheit brooder trays for 24 hours. A control group of three-day-old chickens also was placed in brooder trays, but the temperature was set at 92 degrees F, similar to practices in commercial chicken production. At 42 days of age, both groups were put in a setting with a temperature of 98 degrees, a temperature that can occur during heat waves, particularly in the southern United States.

Blood work taken at various points in the study showed the physiological and biochemical responses to heat stress typical in chickens were reduced in the birds that had been exposed to higher temperatures, or "thermoconditioned," immediately after hatching.

The extent of hormonal response was significantly different between the two groups of chickens, with the response being suppressed in the chickens that had been exposed to the higher temperatures at three days of age. As a result, 50 percent fewer of the "thermoconditioned" birds died from heat stress, compared with the control group.

Heat stress can result in significant losses to poultry producers, both in the time it takes the birds to reach market weight and in deaths of birds. Last summer, a poultry flock at ARS' Henry A. Wallace Beltsville (Md.) Agricultural Research Center lost 20 percent of its chickens due to heat stress.

Additional studies will be conducted to determine how and where control mechanisms in the bird's body are altered in the "thermoconditioned" chickens to enable them to adapt to heat stress.

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

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