Acute heat stress-induced alterations in blood acid-base status and skeletal muscle membrane integrity in broiler chickens at two ages: Implications for meat quality

The effects of acute heat stress (AHS) on indices of respiratory thermoregu lation and skeletal muscle damage (myopathy) were examined in broiler chick ens at two ages (35 and 63 d of age); the relationships of these responses with changes in meat quality were assessed. Exposure to AHS significantly i ncreased deep-body temperatures, panting-induced acid/base disturbances, an d plasma creatine kinase (CK) activities, reflecting heat stress-induced my opathy (HSIM). The extent of the hyperthermia and disturbances in acid/base status and myopathy was significantly (P < 0.05) higher in the older birds . Consistent with AHS-induced alterations in thermoregulatory indices and m uscle membrane integrity were changes in breast muscle glycolytic metabolis m as indicated by lower muscle pH immediately posts-laughter (pH(i)), incre ased water loss, and increased incidence of breast muscle hemorrhages; Valu es of pH(i) were lower and hemorrhage scores greater in the AHS birds at 63 d; drip losses were significantly higher in the 35-d-old birds. Exposure t o AHS did not affect breast meat eating quality, although overall reduction s in flavor attributes were observed in the older birds. We concluded that exposure to AHS induced disturbances in blood acid/base status and had a de trimental effect upon skeletal muscle membrane integrity. Muscle from broil ers exhibited an increased sensitivity to AHS exposure with age. Alteration s in antemortem blood acid/base status and muscle membrane integrity induce d by AHS were associated (though not necessarily causally) with adverse eff ects upon breast meat quality. It is recommended that preslaughter exposure of broiler chickens to AHS should be avoided in order to reduce alteration s in muscle metabolism and membrane integrity and undesirable meat characte ristics.