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→Dietary Sources
==Dietary Sources==
==Dietary Sources==
'''Foods differ in the amount of energy, and this is a primarily a function of the amount of moisture, digestibility, and the amount and proportions of macronutrients'''. Digestibility (i.e., feeding) studies are the most accurate way of determining the ‘available’ energy content of a food, but these studies are expensive and require the use of laboratory animals. Many pet food companies do not have the resources to conduct digestibility studies and use predictive equations instead. There are different predictive equations for pet foods and human foods, which in part reflects differences in the digestibility of these foods. Typically for highly digestible human foods such as chicken breast, egg, rice or oils, the [[Nutrition Glossary#Atwater Factors|‘Atwater’ factors]] [protein (4 kcal per gram), fat (9 kcal per gram), and carbohydrate (4 kcal per gram)] can be used to calculate energy content.
'''Foods differ in the amount of energy, and this is a primarily a function of the amount of moisture, [[Nutrition Glossary#Digestibility|digestibility]], and the amount and proportions of macronutrients'''. Digestibility (i.e. feeding) studies are the most accurate way of determining the ‘available’ energy content of a food, but these studies are expensive and require the use of laboratory animals. Many pet food companies do not have the resources to conduct digestibility studies and use '''predictive equations''' instead. There are different predictive equations for pet foods and human foods, which in part reflects differences in the digestibility of these foods. Typically for highly digestible human foods such as chicken breast, egg, rice or oils, the [[Nutrition Glossary#Atwater Factors|‘Atwater’ factors]] [protein (4 kcal per gram), fat (9 kcal per gram), and carbohydrate (4 kcal per gram)] can be used to calculate energy content.
Two different approaches are commonly used for estimating the energy content of manufactured pet foods. One uses pet foods the [[Nutrition Glossary#Modified Atwater Factors|modified Atwater factors]] of 3.5 kcal per gram of protein, 8.5 kcal per gram of fat, and 3.5 kcal per gram of [[Carbohydrates Overview - Nutrition|carbohydrates]]. Whilst this equation is mathematically simple it has limitations, because it can over and underestimate foods with a digestibility that is lower or higher than ‘average’.
An alternative but more complex equation which does account for differences in digestibility has been developed and this does appear to provide a better estimate of the ‘available’ energy content of the food<ref>Kienzle E, et al. The development of an improved method of predicting the energy content in prepared dog and cat food. J Anim Physiol Anim Nutr 1998; 79:69-79.</ref>.
*'''Step 1:''' calculate carbohydrate (NFE) content: Carbohydrate (NFE; g/100g)) = 100 - (Moisture + Protein + Fat + Ash + Crude Fibre)
*'''Step 1:''' calculate carbohydrate (NFE) content: Carbohydrate (NFE; g/100g)) = 100 - (Moisture + Protein + Fat + Ash + Crude Fibre)
*'''Step 2:''' calculate the Gross Energy (GE) content of the food: GE (kcal/100g) = (5.7 x protein) + (9.4 x fat) + (4.1 x [NFE + Crude Fibre])
*'''Step 2:''' calculate the Gross Energy (GE) content of the food: GE (kcal/100g) = (5.7 x protein) + (9.4 x fat) + (4.1 x [NFE + Crude Fibre])