Plasma and muscle cortisol measurements as indicators of meat quality and stress in pigs

Post-slaughter blood samples and muscle samples were collected from pigs slaughtered at the completion of a live-animal performance trial. There were two lines of pigs in which the halothane allele (n) was segregating. The lines were a lean line selected for rapid lean growth and an unselected fat line. There were homozygous normal (NN), homozygous halothane positive (nn) and heterozygous (Nn) genotypes in both lnes. Cortisol was measured in the plasma of the blood samples and in muscle juice obtained by high-speed centrifugation. Meat quality was assessed using pH, colour, fibre-optic probe, drip loss and cure yield measurements. Plasma cortisol concentrations in the fat line were significantly (P < 0·05) greater than thosein the lean line but concentrations did not differ significantly for the three halothane genotypes. Carcasses classified as dark, firm and dry (DFD) had significantly (P < 0·05) greater muscle cortisol concentrations than those classified as normal. Plasma and muscle cortisol concentrations of carcases classified as pale, soft and exudative (PSE) did not differ significantly from those classified as normal. Correlations between muscle cortisol and meat quality attributes were generally highly significant (r = 0·31 to r = 0·51, P < 0·001) There was a highly significant correlation (r = 0·73, P < 0·0001) between plasma and muscle cortisol concentrations.