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Energy is supplied by dietary nutrients (i.e., fats or oils, carbohydrates, and amino acids) and is necessary for growth and egg production. For poultry, apparent metabolizable energy (defined as gross energy minus losses of energy in feces, urine, and gaseous products) is typically used to express the available-energy content of feed ingredients and complete diets. However, as illustrated in the table below, differences in the metabolizable energy value assigned to feed ingredients of the same name differ substantially among regions. Some of the differences can be attributed to differences in the feed ingredients' moisture content, but even when the metabolizable energy value is expressed on a dry matter basis, the assigned energy values differ. As a result, the calculated energy content of a given diet varies substantially depending on which assigned energy values were used for the individual feed ingredients.

Table values of selected feed ingredients showing differences in metabolizable energy values (as-fed values)

1 Feedstuffs 2008 Reference issue and buyers guide. Feedstuffs, September 10, 2008. Minnetonka, Minnesota, USA.
2 Rostagno, H.S. (ed.). 2005. Brazilian tables for poultry and swine. Composition of feedstuffs and nutritional requirements. 2nd ed. Departamento de Zootecnia, Universidade Federal de Vicosa, Brazil.
3 Centraal Veevoederbureau (CVB). 2008. CVB Table booklet feeding of poultry. CVB-series no. 45. (values of ME for laying hens, "MEIa," are shown)
4 Sauvant, D.,J.-M Perez and G. Tran (eds). 2004. Tables of composition and nutritional value of feed materials. 2nd rev. ed. INRA-AFZ, France.
5 Janssen, W.M.M.A. (ed.). 1989. European table of energy values for poultry feedstuffs. 3rd ed. Spederholt Center for Poultry Research and Information Services, Beekbergen, The Netherlands.

Because energy consumption is the main nutritional factor that determines the rate of egg production, the flock's current rate of egg production (or egg-production curve) is the best indicator of dietary energy adequacy. Comparisons of the flock's body weight with the standards is also helpful in determining if the flock is consuming sufficient energy. See also Feeding the Laying Hen.

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