Energy protein and Amino Acids

The " apparent" metabolizable energy (MEn) and the true metabolizable energy (TMEn) values are used for numerous feedstuffs in poultry rations. The MEn is the gross energy of feed minus the gross energy of excreta after a correction for nitrogen retained in the body. The MEn and the TMEn are similar for many ingredients. However, the two values could differ substantially for some ingredients such as feather meal, rice bran, white middlings and corn distiller's grains with soluble. The MEn is the energy value used by most poultry nutritionists in feed formulation. 

Because chickens and other fowl can adjust their feed intake over a considerable range of feed energy levels to meet their daily energy needs, dietary energy levels are used to set the levels of other nutrients, including protein and amino acids. As a result, the concept of the calorie to protein and amino acids ratio has been used extensively in poultry feed formulation. However, recent research indicated that changes in feed intake of both broilers and layers were not inversely proportional to changes in dietary energy levels. This is particularly true when birds were fed high-energy diets (layers) or moderate to high -energy diets (broilers). Consequently, the use of these specific ratios must be carefully evaluated. Because factors other than dietary energy could also affect feed intake, including ambient temperature (which can have a considerable impact on feed consumption) nutrient density in the ration should be adjusted to provide appropriate nutrient intake based on both requirements and the actual feed intake.