Does early thermal conditioning sometimes fail to improve the resistance of broilers to heat stress?

  • Vasco DE BASILIOa, Fanny REQUENAb, Alicia LEONb, Zoraida VELAZCOb, Michel PICARDc
  • Published 2002


Early age thermal conditioning (TC) by exposing young chicks to 40 C for 24 hours reduces body temperature (Tb) and improves long-term broiler resistance to heat stress. Three experiments were performed under semi-controlled tropical environmental conditions to evaluate the factors affecting TC efficacy. The addition of infrared bulbs during TC reduced growth and increased water intake compared to gas heaters at similar ambient temperatures (Ta). TC consistently reduced the Tb of chickens at 7 and 40 days of age independently of the heat source (– 0.22 C on average). During heat stress after 40 days of age, significant reduction in mortality was observed in the TC chickens when only gas heaters were used in the second experiment. The use of infrared bulbs during the first week of age never resulted in reduced mortality. The third experiment demonstrated late acclimatization when chickens were exposed to natural climatic conditions (Ta varying daily from 26 to 36 C) compared to maximal Ta limited to 31 C by air-conditioning from 30 to 40 days of age. Chickens exposed to natural climatic conditions had lower Tb (– 0.16 C) and resisted heat stress at 38± 2 C at 41 days of age, although 12.6% of the air-conditioned chickens died. The TC effects were maintained on Tb in late acclimatized chickens but no differences in mortality due to TC occurred during heat stress. Inconsistencies between TC experiments arise from an imprecise definition of TC and heat stress conditions, and from the environmental conditions perceived by chickens after TC, which can induce late acclimatization. Persistent reductions in Tb after TC have been consistently measured but these might not be directly responsible for resistance to heat stress. Conversely, of the 525 heat stressed chickens studied during the 3 experiments, 64% of those who had a Tb lower than 40.8 C at 4 days of age (prior to TC exposure) survived heat stress although only 47% of the chicks having a Tb higher than 40.8 C at 4 days did. Further research is warranted on the Tb of newly

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Cite this paper

@inproceedings{BASILIOa2002DoesET, title={Does early thermal conditioning sometimes fail to improve the resistance of broilers to heat stress?}, author={Vasco DE BASILIOa and Fanny REQUENAb and Alicia LEONb and Zoraida VELAZCOb and Michel PICARDc}, year={2002} }