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

Abstract

Pig manure contributes significantly to environmental pollution through nitrogen compounds. Reducing protein in feed can help, but it may lead to damaging behaviors if pigs' nutritional needs are not met. Breeding pigs for higher protein efficiency (PE) is a long-term solution to reduce nitrogen pollution, but concerns about pig welfare remain. We studied 95 pigs involved in a project on the genetic basis of PE on a 20% protein restricted diet to investigate the phenotypic connection between PE and welfare. These pigs represented natural PE variations in the population. At around 100 days, before their PE was known, we observed their behaviors. Only three pigs engaged in tail biting and manipulation of vulnerable regions, but this was not associated with PE. There was no clear link between PE and manipulating pen mates' less vulnerable regions. Such behaviors are normal but can cause stress and injury if carried out excessively due to boredom or stress. Overall, pigs with higher PE showed no major behavioral abnormalities in this study. Considering the lack of genetic knowledge, the risk of increased harmful behaviors when selecting for higher PE appears low when inferred from this purely phenotypic association.

Figure 1

Comparison of fat mass between farrowing series and sexes using 2-sided Games-Howell pairwise tests. P-values are Holm-adjusted and bars are shown only for significant comparisons. From left to right: green: females in first farrowing series, yellow: males in first farrowing series, blue: females in second farrowing series, pink: males in second farrowing series.

Figure 2

Protein efficiency (proportion of protein ingested that was retained in the carcass) in the two farrowing series (left) and sexes (right). Abbreviations: F females, M castrated males.

Figure 3

The percentages of behaviors directed at the body, head, ears, tails, vulva or perineum of all active pig-directed behaviors recorded during all observations. Absolute values are shown below in smaller print. The grouping of the behaviors into damaging (biting directed toward ear, tail, vulva or perineum) or problematic behaviors (manipulation with mouth or nose except for biting towards these vulnerable regions) is illustrated with a blue line, and potentially problematic behaviors (biting and manipulation with mouth or nose to body and head) is illustrated with a green line.

Figure 4

Counts of behaviors directed at or received by pen mates as a function of protein efficiency. (A) Number of problematic behaviors performed, i.e., toward ear, tail, vulva or perineum (ETV), (B) Number of potentially problematic behaviors performed, i.e., toward body or head, (C) Number of problematic behaviors received, i.e., toward ETV, (D) Number of potentially problematic behaviors performed, i.e., toward body or head. Note that the regression line in (A) is quasi-Poisson, for (B) to (D) Poisson (zero-inflation, as well as negative binomial regression lines are not implemented in the function).

Figure 5

Counts of confrontations initiated, their outcomes and straw rooting counts as a function of protein efficiency. (A) Number of confrontations initiated, (B) number of confrontations won, (C) number of confrontations lost, (D) number of straw rooting bouts performed per sex (females in pink, males in blue). Note that the regression line in (A) to (C) is quasi-Poisson, and Poisson in (D) (zero-inflation, as well as negative binomial regression lines are not implemented in the function).