THE EFFECT OF MIXING UNFAMILIAR INDIVIDUALS ON THE GROWTH AND PRODUCTION OF FINISHING PIGS

The effect on productivity of mixing finishing pigs from different litters was studied. Two hundred and ten Yorkshire x Landrace pigs of about 76 kg were assigned in groups of six to each of four treatments. In treatment 1, pigs were retained as unmixed littermates while in treatments 2 and 3, three pigs from one litter were mixed with three pigs from another litter. Additionally pigs in treatment 3 were injected with a tranquilizer prior to mixing. In treatment 4, groups of five littermates were introduced into the pen of either a lighter weight or heavier weight pig. All groups were housed in 6.65 m2 partially slatted pens and fed from a communal food trough. Besides promoting aggression and fighting, mixing significantly depressed productivity, and both short-and long-term economic returns. Over the 3-week experimental period the proportional live-weight gains observed in the unmixed pigs over those of the mixed groups, were substantial: 0.099 over the 3:3 mixed groups, 0.141 over the tranquilizer-treated groups, and 0.127 over the 5:1 mixed groups. Consequently, mixing would necessitate additional inputs of food, housing, and labour because of the increased days to market. The tranquilizer not only did not eliminate fighting but had a long-term negative effect on production and was thus a contra-indicated expense. Introducing a single pig into a group in an occupied pen also lowered production, as did moving without mixing. However, moving effects were short lived and had minimal negative influences on overall productivity.