Improving feed efficiency in pigs : bridging genetics and nutrition

The efficiency of turning a pig diet into a human edible product, commonly called feed efficiency, is key to decrease environmental pollution of the pig industry. In this thesis I bridge the genetics and nutrition expertise fields in pig production. I investigate traits explaining variation in individual feed efficiency in pigs, and their potential to develop more effective nutritional and breeding strategies to improve feed efficiency. This thesis shows that there is variation in feed efficiency traits of grower-finisher pigs associated with variation in faecal digestibility values, independent of variation in feed intake. Also the variation in faecal microbiota composition is shown to be associated with variation in feed efficiency, but the relationship depends on diet and sex. Faecal microbiota is associated to variation in faecal nutrient digestibility as well, and can even be used to predict faecal nutrient digestibility values. Further, this thesis describes the phenotypic variation for individual nitrogen and amino acid efficiency and shows that nitrogen efficiency estimated based on feed intake and growth curves is heritable. The faecal microbiota and serum metabolites are found to be heritable too, and the research described in this thesis shows that there is substantial overlap between variation in feed efficiency explained by the host genome, faecal microbiota composition, and serum metabolite profiles. Hence, in this thesis I show that variation in faecal nutrient digestibility, faecal microbiota composition, serum metabolite profiles, and nitrogen efficiency are associated with variation in feed efficiency, and that there is a genetic background. The characteristics investigated in this thesis could be used to improve feed efficiency in pigs by means of breeding, but also to predict individual grower-finisher performance and aid nutritionist in precision feeding concepts. Likewise, pig nutritionists could help breeders in developing a feeding strategy to express more genetic variation. The results in this thesis support that bridging the gap between genetics and nutrition is the way forward to further improve feed efficiency in grower-finisher pigs