Basic Control Mechanisms of Thermoregulatory Process in Livestock

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BASIC CONTROL MECHANISMS OF THERMOREGULATORY PROCESS IN LIVESTOCK SALAMI SAHEED AYODEJI

Introduction
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different (Wikipedia, 2012). Thermoregulation could also be referred to as the mechanisms and control systems used by the body to balance thermal inputs and thermal losses so as to maintain its core temperature nearly constant (Monique, 2002). This process is one aspect of homeostasis: a dynamic state of stability between an animal's internal environment and its external environment (the study of such processes in zoology has been called ecophysiology or physiological ecology) (Wikipedia, 2012). If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs and any prolonged exposure (longer than a few hours) at this temperature without control mechanisms to bring it back to normal is tantamount to death of the animal. The opposite condition, when body temperature decreases below normal levels, is known as hypothermia. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles (Guyton and Hall, 2006). Animals and humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the animal body, placing it in great danger of injury or even death. For animals, adaptation to varying climatic conditions includes both physiological mechanisms as a byproduct of evolution,

and the conscious development of cultural adaptations (Harrison et al., 1988; Weiss and Mann, 1985). There are four avenues of heat loss: convection, conduction, radiation, and evaporation (Wikipedia, 2012). If skin temperature is greater than that of the surroundings, the body can lose heat by radiation and conduction. But if the temperature of the surroundings is greater than that of the skin, the body actually gains heat by radiation and conduction. In such conditions, the only means by which the body can rid itself of heat is by evaporation. So when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise (Guyton, 2006). During sports activities, evaporation becomes the main avenue of heat loss (Wilmore et al., 1999). Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss (Guyton and Arthur, 1976). The skin assists in homeostasis (keeping different aspects of the body constant e.g. temperature). It does this by reacting differently to hot and cold conditions so that the inner body temperature remains more or less constant. Vasodilation and sweating are the primary modes by which humans attempt to lose excess body heat. The brain creates much heat through the countless reactions which occur. Even the process of thought creates heat. The head has a complex system of blood vessels, which keeps the brain from overheating by bringing blood to the thin skin on the head, allowing heat to escape. The effectiveness of these methods is influenced by the character of the climate and the degree to which the individual is acclimatized.

Classification of Animals by Thermal Characteristics
Based on thermal characteristics, animals could be classified into four broad groups: • Endotherms: These are animals that create most of their heat via metabolic processes, and are colloquially referred to as warm-blooded. Most mammals and humans belong to this group. • Ectotherms: These are animals that use external sources of temperature to regulate their body temperatures. They are colloquially referred to as coldblooded despite the fact that body temperatures often stay within the same temperature ranges as warm-blooded animals. Examples of animals that belong to this group are...
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