Quantifying disease tolerance and disease resilience in the growing pig for the genetic improvement of health: are routinely collected on-farm records enough?

Abstract

The objective of this thesis was to propose a method to quantify the traits of disease tolerance and disease resilience in the pig, using records routinely collected on Australian commercial piggeries. Existing data cannot be used to measure disease tolerance as unbiased estimates require measures of internal pathogen burden. Investigations focused on disease resilience, defined as the ability to maintain performance despite infection challenges in the environment, by utilising both disease tolerance and disease resistance. Variation in resilience can be assessed using a genotype by environment interaction (G×E) approach. On-farm infection challenges cannot be considered independently. Environments quantified by contemporary group (CG) estimates assume to capture all challenges. The performance traits upon which CG estimates are derived were extended to include additional growth traits, daily feed intake, backfat and muscle depth. While alternative traits capture different aspects of the environment, no single trait was consistently superior to assess G×E for growth. All phenotypes should be explored and the ideal trait may be on an individual herd basis. For a measure of only infection challenges, CG estimates were adjusted to remove seasonal effects. Seasonal decomposition was more effective than fitting climatic variables as splines in the models to estimate CG effects. However, the strongest linear relationship with frequency of medication was with the unadjusted environmental descriptor (r = -0.29). This further supports a systems approach for the genetic improvement of health. Since infection challenges may be limited in high-health herds, an alternative health trait was provided. Health defined as a binary trait of medication status was found to be lowly heritable ( = 0.06 ± 0.04). Therefore, there are opportunities to use routinely collected on-farm records for the genetic improvement in not only productivity, but also for health in the growing pig.