Myopathy in turkeys: Are the mechanisms similar to those in broilers and pigs? Effects of halothane

Previous studies in this laboratory described the induction of myopathy in rapidly growing modern broiler chickens by exposure to halothane anaesthesia. It was proposed that the mechanism of this pathology might involve elevation of intracellular calcium through activation of the intracellular sarcoplasmic reticulum (SR) calcium channel or ryanodine receptor (Ryr). Further studies demonstrated that acute heat stress induced myopathy in broiler chickens was ameliorated by treatment with the specific Ryr antagonist dantrolene sodium. These findings further implicated the SR calcium channel in the etiology in spontaneous and stress-induced myopathy in broiler birds. A defective halothane sensitive Ryr in pigs and humans is responsible for malignant hyperthermia syndrome and porcine stress syndrome. Other workers have attempted to establish a link between halothane sensitivity; myopathy and meat quality problems (e. g. a PSE like condition) in both broilers and turkeys but the findings remain equivocal. The present study therefore examined the effects of halothane upon muscle membrane integrity (plasma creatine kinase or CK activity) in a commercial turkey line and related these measures to other physiological responses to the anaesthesia. Groups of 8 turkeys (17kg body weight) were allocated to control, halothane anaesthesia or anaesthesia plus dantrolene treatments. Anaesthesia was of 15 minutes duration. Blood samples and body temperatures were obtained immediately before and after anaesthesia and after 4 hours recovery. Samples were analysed for pH, pCO₂, sodium, potassium and CK. There was no evidence of malignant hyperthermia or acid base disturbance in these birds or of a halothane-induced myopathy. Plasma potassium was elevated by anaesthesia an effect apparently reversed by dantrolene. The findings differ markedly from those in broilers and do not support the hypothesis that the similarities in muscle pathology and meat quality problems in pigs, broilers and turkeys are attributable to the same mechanisms.