A link between heat stress -associated myopathy and “PSE” meat in broiler chickens?

The problem of pale soft exudative (PSE) meat is becoming more common in current broiler lines with its incidence increasing in response to elevated temperatures. Its aetiology may be similar to that reported in pigs where muscle damage and PSE meat in acutely stressed pigs are believed to be caused by alterations in muscle intracellular calcium (Ca²⁺_i) homeostasis. Studies in the authors’ laboratory have shown that myopathy in broilers, associated with selection for fast growth rate and acute heat stress (AHS) is similarly attributable to derangements in muscle Ca²⁺i regulation. Correlations between the degree of heat stress associated myopathy and changes in meat quality attributes were therefore investigated in broilers exposed to AHS. Two groups of 12 male broilers (35d) were held under AHS (31°C/85%RH) or control conditions (21°C/50%RH) for 2 hours in climate chambers. Deep body temperature, blood pCO₂ and pH were measured as indices of thermoregulatory success and effort. Heat stress associated myopathy was determined by measuring plasma creatine kinase (CK) activity. Breast muscle pH, colour and haemorrhage scores and drip loss were measured as indices of poultry meat quality. Birds subjected to AHS exhibited significant hyperthermia and hypocapnic alkalosis. Exposure to AHS induced muscle damage as reflected by a marked increase in plasma CK activity. AHS produced a lower breast muscle pH 15-min post slaughter but had no effect upon the decrease in pH 24 hours later. Muscle haemorrhage scores were significantly higher and drip loss was markedly elevated in AHS birds. Lighter coloured muscle was associated with AHS but did not reach significance. Thus the myopathy appeared to be associated with paler more exudative meat. It is proposed that Ca²⁺-mediated alterations in muscle membrane integrity induced by acute heat stress may result in a “PSE-like” meat condition. It is therefore suggested that myopathy induced by stressful pre-slaughter procedures may precede or mediate alterations in broiler meat quality attributes.