If the stocking density is too high for the size and design of house and ventilation equipment, the temperature may rise dangerously since there will be more metabolic heat being added to the house air than was planned for. Radiant transfer from bird to bird is then greater and stagnant hot air is trapped between the birds.

Although temperature measured with an ordinary thermometer is the simplest single index of thermal strain on birds, there is much more to it than that. Characteristics of the bird which affect heat loss include feather cover and the size of the combs and wattles. Posture has considerable influence on heat loss.