Phenotypic link between protein efficiency and pig welfare suggests no apparent trade-offs for mitigating nitrogen pollution

Abstract

Pig manure is a significant contributor to environmental pollution due to nitrogen compounds. While limiting protein in feed can mitigate this issue, this may result in damaging behaviors if the pigs’ nutritional needs are unmet. One long-term strategy to reduce nitrogen pollution is to breed pigs for higher protein efficiency (PE), but concerns were raised that this may negatively affect pig welfare. To investigate whether PE is related to impaired pig welfare, this study observed 95 non-tail-docked fattening pigs around 100 days old with a 20% protein restriction. Only three pigs were observed engaging in tail biting and manipulation of regions that are particularly vulnerable to injury, and none of these behaviors were associated with PE. Pigs with higher PE tended to initiate and win more confrontations than those with lower PE. We cannot confirm or exclude the influence of PE on the manipulation of pen mates’ less vulnerable regions. Such behaviors are normal and non-damaging per se, but can stress and injure pen mates if carried out excessively due to boredom or stress. Interestingly, increased engagement with straw was not associated with a reduction in potentially harmful behaviors, but we found a significant positive correlation. In conclusion, the study found no major behavioral abnormalities in pigs with higher PE. However, it highlights the importance of considering the potential trade-off between sustainability and welfare, reducing stress and providing adequate environmental enrichment to ensure the welfare of the pigs, especially if they are to become more efficient through breeding.