Mixing pigs at finishing may be necessary to manage the process of emptying barns and/or to maximize facility output.
Previous research in this area has been carried out in university research facilities in the early growth stages, and focused more on behavioral responses than on production parameters.
This collaborative research project with The Maschhoffs occurred in the company’s wean-to-finish facilities. The goal was to determine the effect of mixing finishing pigs on all aspects of performance and aggressive behavior.
Four studies involve more than 16,000 pigs. The impact of mixing on performance related to gender, number mixed, stage of finishing at mixing, frequency of mixing and effect of mixing pigs of similar weight were evaluated. One study also monitored aggressive behavior in mixed and unmixed groups in the days following mixing.
Most studies reflected reduced growth performance in pigs immediately after mixing. However, subsequently, mixed pigs generally had compensatory growth and grew faster than the unmixed. Growth rate and feed efficiency were similar for both groups.
Sufficient time is required to achieve full compensatory growth after mixing, illustrated by one study. Groups were mixed at 182 lb., and performance was monitored for six weeks. During the first four weeks, the mixed-pig growth rate was 8% lower than that for unmixed pigs. But growth rate in the next two weeks was 4.2% greater for the mixed vs the unmixed group.
Overall, mixed pigs grew 4.6% slower and were 4.3 lb. lighter at the end of the study than the unmixed animals.
This study points out that the time it takes to fully compensate in growth performance following growth restriction from mixing will depend on the severity and duration of the restriction, and the time allowed for the pigs to compensate. In this example it would have taken more than six weeks.
In one study that monitored the aggressive behavior of pigs following mixing, pens of 24 pigs were divided into three groups of eight pigs of either light, medium or heavy weight. Three groups of eight pigs of the same weight from three of the original pens were mixed to form a new pen of 24 animals.
The behavior of the mixed-weight groups was then compared with unmixed control pens. The number of fights was greater for mixed vs unmixed groups on each of the four days following mixing. However, the number of fights was similar for the three weight categories, and declined to low levels by the third day after mixing.
Overall, mixing finishing pigs had no impact on morbidity and mortality, and a transitory effect on growth performance and aggression levels.
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