ing NE for ingredients and for pig feed formulation is highly recommended.
Practical aspect of the use of net energy in pigs
The use of NE instead of DE or ME leads to changes in ingredients ranking. When dietary DE and NE values are expressed as percentage of a compounded feed (wheat: 67%, soybean meal: 16%, fat: 2.5%, wheat bran: 5%, peas: 5% …), the feedstuff ranking changes (Table 1). This different hierarchy has a huge impact on the daily feed formulation and on the usage and supply of the feedstuffs in a feed factory. For instance, the NE system allows being less dependant on imported protein sources feedstuffs like soybean meal.
Table 1. Ranking of feedstuffs depending on their digestible energy (DE) or net energy (NE) content. (for details, see EvaPig®)
Lowering the CP level of a feed will change its energy characteristic if the NE content is not controlled. Indeed, the reduction of the CP level in a feed, based on the same ME content does not take into account that the NE will be increased. In low protein diets some of the protein is substituted by starch and/or fat; this substitution has not a marked effect on the dietary ME content but will change the NE content of the feed. Indeed, in the NE system, 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 CP content. 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.
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. Experiments carried out with low protein 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 animals are fed ad libitum (Figure 2).
Figure 2. Effect of low protein, amino acid supplemented diets on carcass quality and growth performance of pigs fed ad libitum (diets were formulated using NE and SID basis; 55 to 105 kg body weight)
The implementation of feed formulation with the NE system, especially for pig, enables a more effective assessment of raw materials and feeds in order to optimize animal performance, carcass traits and feed costs. When amino acid and energy dietary contents are estimated properly, with accurate and practical nutritional systems (SID amino acids and NE), carcass quality as well as pig growth performance can be kept under control.