Alternative rearing systems in pigs: consequences on stress indicators at slaughter and meat quality

The objective of this study was to evaluate the effects of three alternative (ALT) rearing systems for growing pigs (outdoor: 150 m(2)/pig; straw bedding: 1.30 m(2)/pig; and hut with access to a courtyard: 1.30 m(2)/pig) compared with a conventional system (fully slatted floor: 0.65 m(2)/pig, considered as control), on pre-slaughter stress indicators in relation with meat quality. To that end, the number of skin lesions on whole carcasses, as well as blood creatine kinase (CK) activity and urine levels in cortisol and catecholamines (adrenaline and noradrenaline) were determined at slaughter. Glycolytic potential (GP) and ultimate pH of the semimembranosus muscle were also measured. The global correlation network calculated between all these parameters shows that the indicators of pre-slaughter muscle activity (plasma CK) and/or stress indicators (e.g. adrenaline) are negatively (r = -0.26, P < 0.01; r = -0.29, P < 0.05, respectively) correlated with muscle GP and positively (r = 0.17, P < 0.05; r = 0.44, P < 0.001, respectively) with meat ultimate pH. Although some traits measured were sensitive to the degree of pre-slaughter mixing, they differed across rearing systems. The differences were most pronounced for the comparison of outdoors v. slatted floor. The lower levels of plasma CK and urinary catecholamines, and the lower number of carcass skin lesions of pigs reared outdoors, were related to a lower meat ultimate pH. Thus, ALT rearing systems influence animal welfare and meat quality, by providing enriched environmental conditions to the animals.