In animal feeds, energy supply represents a major part of the cost of the formula. Improving knowledge of energy utilization by the animal in order to better meet its needs and having systems in place to evaluate for the energy content of raw materials and feeds are thus a determining factor in least cost formulation.

 

 As for amino acids, the total amount of energy supplied by the feed which is called gross energy (GE) is not available for the animal. Finally, after the different levels of energy utilization, less than 60% of the ingested GE can be used by the animal.

 

 

An energy system is a method for assessing the dietary energy content which corresponds to one or more stages in the utilization of energy by the animal. Systems of digestible energy (DE) and metabolizable energy (ME) take into account the digestive utilization of energy and also the losses in the form of urine and gases for ME. The net energy system (NE) takes into account the metabolic use of energy and the resulting heat production (see also Net Energy Evapig®). EN thus represents the most advanced energy system providing the best estimate of the “true” energy value of a raw material or feed. Such a system thus makes it possible to optimize the composition of a feed and its implementation is increasingly widespread, especially in pig nutrition.

 

 

More on "Managing Carcass quality of growing pigs fed low protein diets"

 

The implementation of diets with low protein content in pigs represents a demonstrative example of the interest of net energy. In these types of diet some of the protein is substituted by starch and / or fat. This modification of part of the energy source, the scope of which depends on the extent of the protein reduction, modifies the energy utilization of the feed. In fact, dietary protein reduction leads to a reduction in DE content, whereas there is no marked effect on ME. In the NE system, however, the efficiency of ME supplied by starch (82%) is greater than that of digestible protein (58%). Therefore, there is an average increase of 0.5% in NE content for every point of reduction in dietary protein content. Moreover, this effect is accentuated in case of substitution of some of the protein by fat, due to its higher efficiency  than that of starch (90% Vs 82%) and its high energy content.

 

Download a reference article published in FeeMix in Pdf (258 Ko): Noblet J. and Tran G., 2004. Estimation of energy value of feeds for pigs. Feed Mix, n°12, 4.

 
On a practical level, it is thus important to take into account this increase in NE associated with the reduction of dietary protein content in order to allow better feed utilization by the animal. The tests carried out with low protein content diets formulated with NE and with adjusted amino acid supplementation levels have shown that growth and carcass adiposity at slaughter are not affected even when the animals are fed ad libitum.

 

The implementation of feed formulation with the NE system, especially for pig, thus enables a more effective assessment of raw materials and feeds in order to optimize animal performance, carcass traits and feed costs.

  

 

Tables of composition and nutritive value of feed materials: pigs, poultry, cattle, sheep, goats, rabbits, horses, fish Sauvant D., Perez J.-M., Tran G. Eds. ISBN 9076998418 2004, 304 p. INRA Editions Versailles For more information please visit INRA and AFZ websites: