Figure 1.

Thermal energy is exchanged between the animal and environment by 3 main processes: convection, conduction, and radiation. In livestock, conduction is generally limited to recumbent positions. Evaporation of sweat and moisture from the respiratory tract is an important mechanism for heat dissipation. Under thermoneutral conditions (A), thermal input from the environment is roughly equal to dissipation, and the animal does not expend additional energy to maintain homeostatic body temperature. During heat stress (B), thermal input exceeds normal dissipation, and the animal must engage in additional processes for heat dissipation to maintain a stable body temperature. When heat stress is extreme, this homeostasis may be lost, resulting in hyperthermia.