Factors influencing the welfare and carcass and meat quality of pigs 2. Mixing unfamiliar pigs

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Abstract
Mixing pigs from different social groups is known to cause turmoil which often results in skin lacerations as well as dark, firm and dry meat. Nine hundred and sixty commercial crossbred pigs were used for this experiment, divided into eight consignments. Within each consignment the pigs were divided into groups of about 15. The pigs in each group had coexisted for at least 6 weeks prior to slaughter. Thirty min before loading for slaughter, groups of pigs were either mixed with unfamiliar pigs or not mixed. Similarly, on arrival at the abattoir, groups of pigs were either mixed or not mixed. Hence there were four possible treatment combinations: pigs mixed with unfamiliar animals at loading, mixed at unloading, mixed at both points, or pigs which had remained in their social groups for at least 6 weeks prior to slaughter. Carcasses were dressed according to normal practice. After 20 h in the chiller room carcasses were assessed for skin blemish and fibre optic probe (FOP) values were measured in the longissimus dorsi muscle. Mixing pigs at either loading or unloading, or at both points, had no significant effect on the FOP value, but it did have a significant effect on the frequency of skin blemish values. Skin blemish values increased due to mixing at the farm (+0·36, Meat and Livestock Commission scale) however mixing at both places did not have an additive effect. The results indicate that the ideal movement system might be to keep pigs in their farm pen social groups until the point of slaughter.