Uniform or heterogeneous weight groups as factors in mixing weanling pigs

Abstract

A series of trials evaluated the behavior and performance of pigs grouped into three main categories at weaning: (1) unmixed litters, (2) mixed into uniform body weight groups (light, medium and heavy) and (3) mixed into heterogeneous weight groups. The effects of grouping on performance criteria were conflicting among trials and with time after weaning. In trial 1, heterogeneous groups had lower (P = 0.09) average daily gain to 5 d after weaning than intact litters. The reverse was observed in trial 2. In trial 3, uniform weight groups grew more rapidly (P < 0.01) than heterogenous groups. These treatment differences persisted through 19 d post-weaning for pigs in trials 1 and 2 but were no longer evident in trial 3. Play/fight behavior was highest (P < 0.01) among uniform weight groups resulting in an increased wounding score for head and shoulders of pigs in medium and heavy weight groups. In trial 1, structures which allowed individuals to hide their heads were available for the first 5 d but did not affect behavior or wounding. In trial 2, pigs from the three main groupings were mixed again on day 19 into three new groupings (unmixed, uniform weight or heterogenous weight). There were no performance differences among the nine grouping combinations 40 d after weaning. We conclude that if litter groups cannot be maintained after weaning, it may be advantageous to mix newly weaned pigs into uniform weight groups although the benefit is not consistently present. If space is limited, the greatest benefit would be to group light weight pigs together.