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Energy

Technically, energy is not a nutrient. In regards to nutrition, energy is the product of oxidation of organic compounds such as CHO, proteins, and lipids. The majority of all biological processes require a source of energy. Quantitatively, the greatest animal requirement is for energy and therefore energy yielding compounds are the greatest component of the diet. In the diet, carbohydrates are the primary source of energy. Carbohydrates are both relatively inexpensive and physiologically appropriate.

In nutrition, there are a range of units used to state the amount of energy produced by oxidation of an organic compound. The first is a calorie (cal). A calorie is defined as the amount of heat required to increase the temperature of one gram of water by one degree Celsius. One thousand calories equals one kilocalorie (kcal). A human Calorie, stated with a capital “C”, refers to one thousand calories or one kilocalorie. One million calories equals one megacalorie (Mcal). Energy is also expressed in terms of joules. One calorie equals 4.184 joules. Module III will discuss additional terms used to identify the energy value of a feed.

Providing the daily dietary energy requirement is essential for optimal productivity. Examples of common effects of energy deficiencies include: decreased production level such as weight gain or milk production, decreased performance level such as speed or endurance, decreases reproduction efficiency such as conception and/or pregnancy rates and increased incidence of metabolic disorders such as ketosis.

The most accurate method to compare interspecies energy expenditures and energy requirements is to compare metabolic body weight (MBW). The equation to determine MBW is: MBW = BW^(0.75). The equation is based on the premise that homeotherms dissipate heat relative to surface area. As surface area is difficult to measure an alternative method was selected. Data supported body weight raised to the 0.75 power provided a relatively accurate measure of basal energy requirement.

In addition to body size, energy requirements are also influenced by a number of additional factors. Some examples of factors that influence energy requirements are activity level, production level, environmental conditions, nutritional deficiencies, and general health. Energy requirements are positively related to activity and production levels. As activity and/or production levels increase, energy requirements also increase. Environmental conditions such as moisture level and air movement will influence energy requirements. Excessively warm air temperature combined with high humidity can induce heat stress. In an attempt to alleviate heat stress, animals will use energy. Cool air temperatures can also increase the energy requirement. Nutritional deficits and illnesses can also increase energy requirements. Energy requirements have the potential to significantly change and to maintain optimal productivity the diet must reflect the changes in energy requirements.

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