Stress reactions at slaughter and meat quality in pigs: genetic background and prior experience

Stress reactions to the slaughter procedure influence ante- and post-mortem muscle metabolism and, consequently, the rate and extent of glycogen breakdown and pH decline, colour and drip loss. Effects are principally due to variations in ATPase activity and muscle glycogen reserves. Behavioural, physiological and metabolic responses to aversive situations depend on genetic background and prior experience of the animals. For example, reactivity to humans depends on breed; compared to Large White pigs, Durocs approach humans more. The effect of slaughter conditions on peri-mortem muscle metabolism depends also on breed; muscles of Durocs were relatively insensitive to slaughter conditions. Prior experience, such as repeated handling, modifies reactivity to familiar and unfamiliar humans. Repeated positive handling during rearing did not modify meat quality of Large Whites. Mild negative handling during rearing changed pre-slaughter muscle metabolism only if the negative handler was present at slaughter. Literature indicates that severe negative handling during rearing may influence peri-mortem muscle metabolism in the absence of the negative handler. Reactivity to humans measured in pigs with no handling experience, weeks or months before slaughter, may predict pre- or post-slaughter muscle metabolism. Thus, physical and visual contacts with the human, established by the pig, were negatively correlated with post-bleeding muscle temperature and ultimate pH. Fighting during mixing was positively correlated with ultimate pH and colour. Up to 42% of variability in ultimate pH in pigs of similar genetic and rearing background could be explained by fighting during mixing and reactivity to humans. Fighting during mixing could be predicted by fighting during a food competition test and levels of exploration of an unfamiliar object. Overall, results show that the technological meat quality indicators studied were little influenced by positive or mildly negative handling experience during rearing. In contrast, genetic background, slaughter conditions and behavioural characteristics of the pig, established early in life, explained a large part of variability in a number of technological meat quality parameters.