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The capacity of survival of the chickens to heat stress is increased by early-age thermal conditioning

INRA Prod. Anim., 15(4), 235-245.


1 Universidad Central de Venezuela, Facultad de Agronomia, Apdo. 4579, Maracay, Venezuela 

2 INRA, Station de Recherches Avicoles, 37380 Nouzilly, France

Heat stress during the last week of growth induces hyperthermia and kills a great number of broiler chickens. Body temperature can be considered as an useful indicator of the thermic comfort of broilers exposed to heat and of their capacities of adaptation. Early-age thermal conditioning by exposure of chicks, during 24 hours to 36-40°C, reduced in a limited way (0.12-0.30°C) but significantly and consistently the average temperature measured in the final colon and decreases mortality due to heat stress during the finishing period, without reducing growth. Several results suggest an increased muscular synthesis due to early-age thermal conditioning. These results of research were reproduced under tropical conditions in Venezuela. The mechanisms of early acquisition of a durable resistance to a heat stress are not completely known. Early-age thermal conditioning reduces hematocrite, blood viscosity, blood level of T3, without changing significantly those of glucose and proteins. No result confirms an implication of heat shock proteins in the early acclimation process. Early-age thermal conditioning probably induces thermolysis mechanisms (peripheral blood flow and panting) and reduces thermogenesis under warm conditions (thyroid metabolism and mitochondrial uncoupling), in young chicks when they become homeothermic. There are enough positive results today to assert that the capacity of chickens to survive heat stress is increased by exposure to high temperature during 24 hours at the age of 5 days.

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