The respiratory system also is involved in communication by sound and pheromones and is important in thermoregulation metabolism of endogenous and exogenous substances and protection of the animal against inhaled dusts, toxic gases, and infectious agents. This results in less energy available for exercise or weight gain, and the owner notices the animal’s poor performance. In animals with respiratory disease, the energy cost of breathing can increase. Surprisingly, these variations are normally accomplished with only a small energy cost. Gas exchange requirements vary with metabolism and may increase up to 30 times during strenuous exercise (Figure 45-1).

Athletic species such as the horse and dog have greater mitochondrial density and therefore greater than do less athletic species of similar body size such as the cow and goat. Maximal oxygen consumption ( ) is directly related to the total mass of mitochondria within the skeletal muscles.

When animals exercise, their muscles need more oxygen, which leads to an increase in oxygen consumption. Because smaller species have a greater surface area to body weight ratio, they have a greater surface for heat loss and less heat storage capacity so they need higher basal metabolism to generate more heat. This difference is largely due to the metabolic requirements necessary to maintain constant body temperature. For example, the 20-gram mouse consumes six times more oxygen per unit body mass than does a 70-kg pig. The consequence of this relationship is that smaller species consume more oxygen per kilogram of body weight than do larger species. Basal metabolism, the metabolism of the resting animal, is a function of metabolic body weight (M 0.75). Oxygen consumption and carbon dioxide production vary with the metabolic rate, which is dependent on the animal’s level of activity. The respiratory system provides oxygen (O 2) to support tissue metabolism and removes carbon dioxide (CO 2). The Respiratory System’s Primary Function Is the Transport of Oxygen and Carbon Dioxide Between the Environment and the Tissues

Dead space in the lungs