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Acclimation to heat during incubation: 4. Blood hormones and metabolites in broilers exposed to daily high temperatures

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

^* Ege University, Faculty of Agriculture, Department of Animal Science, 35100 Izmir, Turkey; Laboratory for Physiology, Immunology, and Genetics of Domestic Animals, Department of Biosystems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 30, 3001 Leuven, Belgium; Celal Bayar University, Akhisar Vocational Training School, 45040 Manisa, Turkey; 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 objective of the present experiment was to study the effects of parental age and heat acclimation of embryos on blood metabolites and hormones of broilers exposed to daily cyclic ambient temperatures from d 21 to 42. Eggs obtained from 32 (younger), 42 (middle-aged), and 65 wk (older) breeders were divided into 2 groups. One group of eggs was incubated at control incubation temperature (IT_CONT), whereas 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 1 to 21 d. From d 21 to 42, half of broilers/incubation temperature/parental age was kept as the control (AT_CONT), whereas the other half was exposed to daily cyclic heat treatment (AT_HIGH) to impose a stress response. There was a reduction in plasma triiodothyronine (T₃) levels in IT_HA broilers. On d 28, plasma T₃ levels were similar regardless of parental age of eggs incubated at IT_CONT, whereas IT_HA resulted in lower levels of T₃ in broilers from 65 wk parents. At the same age, AT_HIGH reduced plasma triglycerides with the effect greater for IT_HA than IT_CONT broilers. Plasma uric acid was also lower for IT_HA than IT_CONT broilers for the offspring of 65 wk parents on d 28. There was an increase in plasma creatine kinase activity on d 42 in AT_HIGH broilers regardless of parental age and incubation temperature. Plasma corticosterone was consistently lower for the IT_HA than IT_CONT treatment, being significant on d 21 and 42. It was concluded that these changes in blood metabolites and hormones may enhance the thermoregulatory ability of IT_HA broilers when exposed posthatch to daily high temperatures.

Key Words: broiler • heat acclimation • blood metabolite • hormone