Pre-Conditioning for Hot Weather May Aid
Birds By Sharon
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
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
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.