Thermal balance of livestock: 1. A parsimonious model

A mathematical model based on the physics of heat transfer was developed to predict the components of heat loss from a homeothermic animal in relation to environmental conditions. The animal’s trunk was treated as three concentric insulating cylinders around a heat-generating core, representing the body tissue, coat and surrounding environment. The model also accounted for heat losses from appendages. The model inputs were the hourly meteorological data, parameters and/or variables of animal physiology, and the thermoregulatory responses of different species to environmental conditions. The heat loss components were calculated by iteration of the heat balance equations, assuming steady heat flow. For illustration, the heat balance of a sheep outdoors is predicted from hourly weather data.