Pig Behavior Studies With Practical Implications for Commercial Swine production - Study II.

Livestock Update, April 1995

Allen Harper, Tidewater AREC

This study, conducted at the University of Illinois, was designed to evaluate the effect of regrouping pigs during the late finisher phase on growth performance. The idea was to simulate what actually happens on commercial hog farms when the heaviest finisher pigs are removed at selling time and the remaining lighter pigs are regrouped into fewer pens within the finishing barn. There were three treatments that were imposed on 396 finisher pigs with an average initial weight of 184 lbs. Treatments included a control group in which pigs were placed in pens with familiar penmates, a mixed group in which pigs were mixed and placed in pens with unfamiliar penmates, and a mixed for 24 hours group in which pigs were penned for 24 hours with unfamiliar pigs then returned to pens with their original penmates for the remainder of the trial. The trial lasted two weeks after treatments were imposed. Recorded observations included various aspects of pig behavior (fighting, eating, standing and lying), growth rate, and feed conversion efficiency.

Performance results averaged across the entire 2-week period showed that the mixed pigs grew slowest (1.69 lbs/day) and the unmixed control pigs grew at the fastest rate (1.91 lbs/day). Growth rate for the pigs mixed for 24 hours at the onset of the trial was intermediate (1.75 lbs/day). Fighting behavior during the first day was significantly higher in all mixed pens than in the control pens. Fighting behavior continued to be higher for the mixed pig groups through day 8 but the amount of time spent fighting was greatest during the first day after mixing. The mixed for 24 hour treatment pigs returned to a low level of aggression after they were repenned with pigs familiar to them.

The experiment suggests that the initial severe fighting that occurs immediately after mixing has negative impacts on performance and there continues to be additional stress that impacts performance beyond the first 24 hours after mixing. It is generally accepted that mixing nursery or grower pigs causes aggression that impairs performance initially but pigs recover after the pen social order is established. In the case of finisher pigs the time necessary to allow pigs to set up a new social order and for performance to recover may not be adequate for normal marketing times. Therefore, regrouping lighter finishing pigs after marketing their heavier penmates will result in slower growth and increased days to market weight for the regrouped pigs.

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