Modelling the effect of heat stress on food intake, heat production and growth in pigs

A heat balance model was combined with a food intake model and a metabolism model, to form a larger model which estimates a pigʹs response to heat stress. The combined model was implemented as a computer program, and used to calibrate, test and validate parts of the heat balance model. Heat transfer modes considered were convection, radiation and evaporation of water at the skin, and heating and humidification of air by breathing. Sensitivity analysis revealed a large effect of air temperature, humidity and velocity on heat loss, especially in a hot environment. It also showed that wetting of the pigʹs skin is the most effective means to alleviate heat stress. The calibration procedure confirmed that characteristics related to heat tolerance in pigs must be re-evaluated, due mainly to the changes brought about by genetic improvement (such as reduced backfat thickness). The model was challenged using two different data sets. Although simulated results varied in the same way as measured data, more research is needed to determine more precisely some of the parameters. Long-term predictions were more reliable than those for short (1-day) periods.