An animal must be transported in an environment in which it can maintain its body temperature, becoming neither hyperthermic nor hypothermic. Due to the many and often interacting physiological and environmental variables that can affect body temperature, it is impossible to specify exact ambient temperature ranges that guarantee that animals will remain homeothermic during transportation. The thermal requirements of animals vary widely depending on age, physiological state, and the environment in which they were previously housed and to which they have adapted. For example, newborns are less tolerant of thermal extremes than adults, and late-pregnancy and lactating animals are less tolerant of heat. In addition, animals previously maintained in cold environments with high feed intakes and high rates of resting heat production (Young, 1975) do not tolerate heat as well as animals previously maintained in a hot environment with low feed intakes and low metabolic rates (NRC, 1981). The effect of the higher rates of heat production associated with pregnancy, lactation, and cold acclimation is an increase in the amount of heat that animals must dissipate as environmental temperatures approach and exceed body temperature, that is, a reduction in heat tolerance.
It could be suggested that homeothermic animals be transported in ambient temperatures within their TNZ. The range of the TNZ for most agricultural animals is large, allowing for safe transportation over a relatively wide range of ambient temperatures (see Table 3-1). The Livestock Weather Safety Index was developed to guide decision making for transporting swine during weather extremes (Livestock Conservation Institute, 1970). More information about the Livestock Weather Index can be found at the National Institute for Animal Agriculture (formerly known as the Livestock Conservation Institute) website:
The TNZ for the more common research animals (rodents, cats and dogs, and nonhuman primates) is narrower than in livestock. However, upper limit of the safe range for transport of those animals is also based on the UCT of an animal’s TNZ. Unlike humans, who can maintain their body temperatures above their TNZ through sweating, most research animals are nonsweating species and have a limited capacity for dissipating heat.
Though the highest ambient temperature at which those animals can maintain their body temperature is close to the upper limit of its TNZ, the lowest ambient temperature at which those animals can maintain their