Thermal Challenges

Thermal challenges, either hot or cold, are common to all animals. Typically, these challenges to homeostasis are nonconsequential. The body's physiologic mechanisms respond appropriately by either evoking mechanisms to create heat, such as increasing metabolism, or to decrease heat load by sweating or diverting blood flow. Behavioral adjustments are made in concert with the physiologic mechanisms. Swine will seek a wallow during periods of elevated temperatures to cause evaporative cooling (swine must use an external water source because they do not sweat), while cattle will seek shade and may stand in water to cool themselves. The inability of livestock to appropriately warm or cool themselves has severe consequences on health. Mortality and morbidity due to hypothermia and hyperthermia can be high. Typically, livestock are most susceptible to these conditions when being transported. Wind chill will greatly reduce the ability of livestock to maintain body temperature during cold, wet weather. Similarly, overcrowding trucks with animals destined to slaughter when ambient temperatures are high will easily cause a percentage of the animals to ''go down,'' or die during transit. Another area of concern for hypothermia and hyperthermia is in feedlot cattle. Due to the weight and condition of these animals, heat waves can easily claim the lives of a significant number of cattle. During winter months, a lack of attention to keeping the feedlot dry will result in losing cattle from hypothermia because as the hair on the cattle becomes more matted, it loses its ability to insulate. Losses due to hypo- and hyperthermia result from the inability of the stress response to maintain homeostatic conditions in the body.

Environmental conditions relative to thermal environment are critical for newborn livestock. Piglets and chicks require a thermal environment approximately 15 degrees warmer than their dam. This is due to their inability to generate adequate heat as compared to other neonatal livestock. Calves and sheep possess brown adipose tissue at birth. Brown adipose tissue has a high content of mitochondria, which allows the neonates to generate body heat. However, piglets and chicks lack this type of adipose tissue and thus must rely on the warmth of their dam and external heat sources (a heat lamp is commonly used in production) to maintain their body temperature. The inability of neonates to maintain body temperature quickly leads to hypothermia and death.

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