Negative social behaviors between pigs can cause stress, which can compromise welfare. There has been significant interest in exploring the effect of diet on negative social behaviors and the wider social behavior repertoire of pigs. The aim of this study was to determine the effects of dietary lysine and tryptophan levels, 2 amino acids found in pig feed, on the social behavior of commercially housed pigs. A total of 2,293 castrated male pigs were randomly allocated to 1 of the 6 treatments in a factorial arrangement: High lysine and low tryptophan, high lysine and medium tryptophan, high lysine and high tryptophan, low lysine and low tryptophan, low lysine and medium tryptophan and low lysine and high tryptophan. Behavior and lesion data were collected. There was a significant effect of lysine level on ear biting behavior, with pigs on the low lysine treatments showing a higher level of ear biting behavior. We also found a significant effect of the interaction between lysine and week on the proportion of pens showing ear lesions and a significant effect of the interaction between lysine and tryptophan and the interaction between lysine and week on the proportion of pens showing severe ear lesions. In conclusion, the lysine content of feed can affect the social behavior of pigs, specifically ear biting, in commercial conditions.

Read the full article in the Journal of Animal Science.