Theoretical model of heat balance in pigs

A theoretical model was developed to predict the heat balance and body temperature of growing and finishing pigs subjected to different environments. The heat transfer modes considered in the model were convection to the surrounding air, conduction to the floor, long-wave radiation between the animal and the surrounding walls, short-wave radiation from the sun, evaporation on the skin surface, evaporation and heating of air in the respiratory tract and heating of ingested food and water. The heat balance is the net heat gain or loss from the environment due to all these processes, added to the animal's heat production. Body temperature is calculated over time using the heat balance, the animal's mass and the specific heat of the animal's body. Behavioural responses to heat and cold environments, such as vasoconstriction, vasodilatation, posture changes and huddling were expressed as changes in heat transfer coefficients and exposed surface area. The increase in evaporation under hot conditions was also considered. It was assumed that the animal's reaction to the environment may be expressed as a function of mean body temperature. The animal's heat production was considered an input to the model, which should reflect the increased metabolic rate in cold environments. Although further research is still needed to determine precisely some of the parameters, the model may be integrated with other models in order to compose a complete pig model.