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Acclimation to Heat During Incubation: 3. Body Weight, Cloacal Temperatures, and Blood Acid-Base Balance in Broilers Exposed to Daily High Temperatures

S. Yalçin^*,1, M. Çabuk, V. Bruggeman, E. Babacanolu^*, J. Buyse, E. Decuypere and P. B. Siegel

^* Ege University, Faculty of Agriculture, Department of Animal Science, Izmir, Turkey; Celal Bayar University, Akhisar Vocational Training School, Manisa, Turkey; Laboratory for Physiology, Immunology, and Genetics of Domestic Animals, Department of Biosystems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 30, 3001 Leuven, Belgium; and Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306

¹ Corresponding author: servet.yalcin{at}ege.edu.tr

The aim of the present study was to investigate the effects of parental age and heat acclimation during incubation on BW, cloacal temperature, and blood acid-base balance in fast-growing broilers exposed to daily cyclic high ambient temperatures from 21 to 42 d posthatch. Eggs obtained from 32- (younger), 42- (middle-aged), and 65-wk-old (older) breeders were divided into 2 groups. One group of eggs was incubated at the control incubation temperature (IT_CONT) and the second group was heat acclimated at 38.5°C for 6 h/d from d 10 to 18 of incubation (IT_HA). Chicks were reared at standard brooding temperatures from d 1 to 21. From d 21 to 42, half of the broilers per incubation temperature and parental age were kept as controls (AT_CONT) and the other half were exposed to daily cyclic heat treatment (AT_HIGH) to impose a stress response. The reduction in BW at AT_HIGH was more pronounced for progeny from older compared with younger parents. However, this reduction in BW was more or less abolished for broilers from eggs incubated at IT_HIGH, implying an increased tolerance to heat stress. Compared with IT_CONT, IT_HA reduced BW of broilers from 32- and 42-wk-old parents while having no effect on those from 65-wk-old parents when reared at AT_CONT. Higher blood pH, and lower partial pressure CO₂ and HCO₃^– at AT_HIGH were associated with greater cloacal temperatures throughout the heat stress from d 21 to 42. Increases in cloacal temperature by AT_HIGH were greater for IT_CONT than for IT_HA broilers. The AT_HIGH and IT_HA broilers had lesser blood partial pressure CO₂ concentrations than AT_CONT and IT_CONT, respectively. Although at AT_HIGH, blood HCO₃^– was lower for broilers from all parental ages, it was more pronounced for those from 65-wk-old parents. It is concluded that these changes in blood acid-base balance reflected adaptive responses to heat stress, and incubating eggs at IT_HA improved thermotolerance of fast-growing broilers.

Key Words: parental age • heat acclimation • broiler growth • blood acid-base balance • cloacal temperature

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				S. Yalcin, V. Bruggeman, J. Buyse, E. Decuypere, M. Cabuk, and P. B. Siegel Acclimation to heat during incubation: 4. Blood hormones and metabolites in broilers exposed to daily high temperatures Poult. Sci., September 1, 2009; 88(9): 2006 - 2013. [Abstract] [Full Text] [PDF]