In terms of nutrition, feeding newly-weaned pigs, low complexity diets increases their susceptibility to disease. The optimum inclusion level of fish oil in corn and soybean meal based nursery diets is about 2.5%, reducing the dietary ratio between omega-6 and health benefit providing omega 3 fatty acids from about 18 in diets with no fish oil to 3.

strides are being made in genetically selecting pigs that have improved resistance to multiple pathogens or a particular pathogen (i.e., PRRSV), or to identify genetic defects that may render pigs more susceptible to disease. Based on these approaches various genetic markers have been identified.

On-farm studies are conducted in Ontario to establish the prevalence of a number of pathogens on different farms and among pigs within farms, to relate pathogen load to reductions in animal performance, to identify so- called biomarkers for pathogen load and reduction in performance, and to establish the effect of pig genotype and feeding-programs on the pig’s ability to cope with pathogens. These studies illustrate the large variability in nursery pig performance in Ontario, and the close association between expression of some genes in the liver, as well as plasma levels of selected cytokines and acute phase proteins, with nursery performance. These relationships should be explored further and will help us to identify approaches to minimize the negative effects of sub-clinical disease on pig performance, wellbeing and profits.