Breeding tolerant pigs for health and productivity

The majority of Australian piggeries rely on antibiotics classified as 'low' importance in human medicine (Jordan et al., 2009). However, there is evidence of antimicrobial resistance to pathogens sampled in pig carcases that are of significant importance to human health, such as 'Escherichia coli' (Smith et al., 2010). With increasing consumer awareness of medicine use and pressure for more welfare-friendly approaches in agriculture, pig breeders are faced with finding alternative strategies for production. The environment of the pig may be a determinant of disease manifestation, and although its control to meet pig requirements improves production and reduces stress (Black et al., 2001), it may neither be economically feasible nor necessarily possible in all circumstances. For example, biosecurity practices and controlling environmental factors have their limitations once a disease outbreak has occurred on a farm. Pigs selected in high health environments usually observed in nucleus herds may not perform as well in the more challenging environments possibly observed on commercial farms. One strategy to maintain health is to improve response to pathogens, through blocking entry and infection, or minimising the effects of infection. That is, selection for the host defence mechanisms of disease resistance or tolerance.