DISPOSITION OF DIETARY ENERGY:

 FECES           URINE           HI                    MAINTENANCE      EGGS AND TISSUES

 800                 300                  600                  1500                            800

4000 Kcal/KG GE

3200 Kcal/kg DE

2900 Kcal/kg ME

2300 Kcal/kg ME

The above data illustrates the proportional relationship in the disposition of energy ingested as a layer diet. Energy is lost or utilized at various stages following consumption of diet by the hen. The values shown in the diagram indicate that of 4000 Kcal contain in one kg of a particular diet, 2900 Kcal are capable of being metabolized by hen and about 2300 Kcal are net energy available for maintenance and transfer into body tissues and egg. The relative amounts of both ME and NE will vary with the composition of the feedstuffs in the diet. Other factors such as species, genetic background, and age of poultry as well as the environmental conditions, also influence the precise distribution of dietary energy into the various compartments.

ENERGY REQUIREMENTS:

Poultry tends to eat to satisfy their energy requirements if fed ad-lib. It is accordingly possible, within limits, to regulate the intake of all nutrients, except water, by including them into the diet in a specific ratio to the amount of available energy in the diet. The importance of considering the energy content of the diet in order to promote the desired intake of all nutrients is therefore, of obvious importance.

An absolute requirement for energy in terms of Kcal/kg of diet cannot be stated because poultry adjust their feed intake to obtain their necessary daily requirements. Chickens fed low energy diets of about 2600 Kcal/kg have been recorded as eating as much as 30% more than similar birds fed diets containing 3200 Kcal/kg. Thus in comparison to high energy diets, low to moderate energy levels allow birds to eat more and therefore, to consume greater amounts of nutrients unless lesser concentrations of nutrients is used. If a higher concentration of energy is used in a diet, feed composition will be reduced; dietary concentration of nutrients should accordingly be increased in proportion to dietary energy in order to assure ingestion of required amounts. Diets with higher concentration of energy are usually more efficiently utilized in terms of unit amount of gain per unit amount of feed consumed.

Feed intake is controlled by certain areas of brain that are believed to regulate the fill capacity of the crop as well as its empty rate. There is also a relationship between feed content of the small intestine and the rate of crop empty. Thus gastro-intestinal fill influences the areas of the brain controlling feed intake. Essential Amino Acid likewise influence feed intake either through their concentrations in the blood, coursing through the brain, where they influence other bran receptors, or by influencing the metabolism of the feed in the liver.

Deficiency or excess of the certain  E.A.A.s cause feed intake to decline by influencing the areas of the brain controlling feed intake. Forced feeding of diets deficient in those A.A.s will increase weight gain compared with that when chicks are fed the same diets ad libitum . There is considerable controversy over whether glucose levels in the blood of birds have any effect on regulating feed intake.

Environmental temperature has a marked influence on feed intake the warmer the environment, the lower the feed consumption. Feed consumption will decrease about 1.5% for each rise of 1°c above the thermoneutral zone. Conversely colder temperatures cause increase in feed consumption. Diets marginal in a particular nutrient may perform better under colder environments, because the birds eat more than at higher temperature and thus consume a sufficient amount of the marginal nutrient. It follows, therefore, that the necessary concentrations of nutrients in a diet are related to the environmental temperature to which the birds eating the diet are exposed.

Other variable factors affecting dietary requirement for energy in addition to those of nutritional balance, temperature, and the physical form of the feed are stress, body size, feather covering and rate of growth or egg production. Poultry through genetic inheritance and environmental circumstances have a certain potential for performance. The level of dietary energy and the associated nutrient balance should facilitate expression of this potential. Under practical conditions, economic considerations may play some limitations on the level of nutritional efficiency that is achieved.