Environmental stress and the physiology, performance and health of ruminants.

A satisfactory environment is one that satisfies the following four criteria: thermal comfort, physical comfort, disease control and behavioral satisfaction. Environmental stress, which may be direct or indirect, is anything that departs from these criteria. Analysis of environmental stress is best achieved by the statistical approach, obtaining correlations from large numbers of animals in natural environments with the experimental approach, and a proper analysis of these correlations into probable causative effects. The amount of scientific attention devoted to thermal stress in ruminants has been very large, yet its practical importance compared, e.g., with environmental stress and disease is relatively small. The most important environmental stresses today are those that have resulted from housing and other attempts to ameliorate the thermal environment. These include air pollution, physical injuries from building surfaces and the extremes of confinement. The contribution of environmental stresses to injury and to diseases such as mastitis and calf pneumonia are discussed and schemes are proposed for future experiments designed to analyze interactions between environment and disease. Examples are also given of approaches to the analysis of the stress of behavioral deprivation.