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Introduction Nutrient requirements have been commonly established in an environment protected from climatic extremes. For that reason, such requirements are most relevant during optimum environmental conditions and are less appro- priate when animals are exposed to stressful environments. Despite the gen- eral awareness that energy demands are increased by cold and that the mag- nitude of those demands is moderated by total body insulation, few quantitative data exist relating environment, nutrient need, and productive efficiency. The latter relationship is particularly important since, in an era of limited resources, it may be necessary to identify the trade-offs between im- proved production of meat, milk, or eggs in a controlled environment and the capital investment and energy input necessary to create an optimum environ- ment. It may, in fact, be more sensible to settle for something less than max- imum performance if such performance does not justify the cost. Only recently have objective bases been developed to guide livestock pro- ducers in altering nutrient inputs in response to environmental change for op- timizing productivity or economic return. Existing nutrition-environment models are rudimentary but can be used to compare the cost of extra feed to maintain body temperature in cold weather versus the cost of providing a warm building, bedding, or other alternatives. Such models include the "op- erational characteristic" of growth for beef cattle, swine, and poultry related to feed energy levels (Teter et al., 1973), the "lower critical temperature" model for beef cattle to estimate lower critical temperatures in still air and wind (Webster, 1974), and the "BOSCOM" model for growth of beef cattle during the finishing phase, which estimates dietary energy requirements in
2 Introduction relation to diurnal and seasonal fluctuations in temperature (Paine et al., 19741. The "effective temperature" model for pigs estimates heat produc- tion required to maintain body temperature by adjusting ambient temperature for air velocity, mean radiant temperature, and the type of contact surface (Mount, 1975~. The ''production', model for laying hens (Emmans, 1974) and the "protein-energy-temperature" model for turkeys (Waibel, 1977) es- timate nutrient requirements for egg production and growth, respectively, as they vary with temperature. Limited data are available to evaluate trade-offs during hot weather, and existing nutrition-environment models do not ac- count for temporary excursions from the thermoneutral zone, which may be of little consequence because of adaptive and compensatory mechanisms (Hahn, 1981~. The general purpose of this report is to collect, interpret, and integrate re- search findings to develop a foundation of information pertinent to nutritional-environment interaction. Then species-specific discussions of current concepts of nutritional management during environmental stress are presented. Although attempts have been made to unify terminology, contri- butions of different authors have not been molded to any particular scheme. It is hoped this approach will be valuable in gaining a thorough understand- ing of adjusting nutrient requirements to deal with existing environments and will therefore aid in developing rational managerial decisions.
