Acclimation to Heat During Incubation: 3. Body Weight, Cloacal Temperatures, and Blood Acid-Base Balance in Broilers Exposed to Daily High Temperatures
2008
Yalçin, S. | Çabuk, M. | Bruggeman, V. | Babacanoğlu, E. | Buyse, J. | Decuypere, E. | Siegel, P.B.
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 (ITCONT) and the second group was heat acclimated at 38.5°C for 6 h/d from d 10 to 18 of incubation (ITHA). 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 (ATCONT) and the other half were exposed to daily cyclic heat treatment (ATHIGH) to impose a stress response. The reduction in BW at ATHIGH 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 ITHIGH, implying an increased tolerance to heat stress. Compared with ITCONT, ITHA 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 ATCONT. Higher blood pH, and lower partial pressure CO₂ and HCO₃⁻ at ATHIGH were associated with greater cloacal temperatures throughout the heat stress from d 21 to 42. Increases in cloacal temperature by ATHIGH were greater for ITCONT than for ITHA broilers. The ATHIGH and ITHA broilers had lesser blood partial pressure CO₂ concentrations than ATCONT and ITCONT, respectively. Although at ATHIGH, 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 ITHA improved thermotolerance of fast-growing broilers.
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