The use of net energy as a more precise system to formulate swine diet

Feeding swine is the most important cost of pork production accounting for up to 70% of the variable costs. Within feed price, energy appears as principal factor affecting price. Optimal energy system is very important in order to control cost and best meet animal needs. Net energy system is currently the most suitable system for animal deposition and has already been adopted by about 50% of the worldwide swine feed production operation.

The global animal nutrition industry is moving rapidly towards precision feeding. And this is all about retrieving the most accurate nutritional values to better match the needs and better predict how animals react to the formulated diets. Having the most accurate data available is crucial in times with high raw materials prices and the increased use of by-products and alternative feed ingredients in pig diets. Wasting or overfeeding nutrients only makes the feed costs rise and energy is one of the most important parameters of the diet. In this article, we explain the benefits of using Net Energy values over Digestible or Metabolizable Energy values to better predict swine performance and optimise diets and production efficiency.

Energy flow losses

Protein, fat and starch, all provide energy to the animal for maintenance and production (growth (meat) and/or milk). These nutritional values can be based on feed tables or feed analysis (such as NIR or wet chemistry). Different energy flows are presented on Figure 1. Over the years, we have made significant steps to make these values more accurate. From gross energy (GE), we moved to digestible energy (DE) or metabolizable energy (ME) in feed formulation. This change is similar to the one made for nitrogen metabolism and the use of digestible amino acids instead of crude protein.

DE is the amount of energy in the feed minus the energy lost in faeces, whereas ME also considers the energy lost in the urine. Urinary energy depends greatly on the urinary nitrogen excretion. The latter depends in turn, on the (digestible) protein content of the diet, varying according to the stage of production. A part of the energy losses is not considered in the DE or ME: the heat production. It corresponds to the loss of energy due to digestive and metabolic processes (the so-called heat increment, HI). To be more precise and not overfeed valuable nutrients, it is recommended to move to the next accuracy step and use the net energy (NE) system which is considering this heat increment. Net energy is therefore the “final utilization of ME” (e.g. for animal maintenance, protein gain vs. fat gain vs. milk production), with its coefficient varying according to the chemical characteristics of the feed because nutrients are not used with the same efficiencies.

Besides, NE values don’t have to be measured but can be calculated from the DE or ME values. The transformation of GE to NE is described by three steps as shown in Figure 1. On average, a complete feed might be characterized by 4 different energy values: 100, 75, 72, 54 kcal/kg for GE, DE, ME and NE, respectively. Thus 100 kcal GE might be equal in average to 54 kcal NE.

Net energy use in feed production and performance

The usage of net energy values is not something new. These values are common in pig feed formulation for many years already and widely adopted (mainly) in Europe. The reason for adoption by the swine sector has been spurred by the competitiveness and the introduction of more by-products in swine diets in the 80s and 90s (that often comes with variable nutritional values, hence the demand for accurate energy values). Net energy system is associated with change in raw materials hierarchy and subsequent change in feed formula. This modification of RM hierarchy is explained by the difference in efficiency of nutrient conversion by swine. Indeed, high fat (animal or vegetable fat, oil seeds) or high starch (tapioca, cereals) ingredients are favoured in the NE system, whereas protein rich and/or fiber rich (meals, fibrous byproducts) ingredients are penalized (Figure 2). Ever since, the use of NE values in swine has been successful and shown to be valuable, validated and robust.

Diets with low crude protein and/or high fat contents can be considered as low heat increment diets and are more suitable for performance as demonstrated in large number of studies. In addition, low heat increment is also potentially better tolerated under heat stress conditions. In the specific case of low-protein diets, which are more and more recommended in order to reduce the impact of pig production on the environment, it is clear that their energy value is underestimated when formulated on a DE or ME basis. This may explain the tendency of fatter carcasses when low-protein diets are formulated on a DE basis: animals are actually getting more energy than expected from DE supply. This also illustrates the importance of formulation criteria for interpreting performance results and the risks of manipulating the composition of diets according to inaccurate or inappropriate nutritional criteria. The use of ileal digestible (or available) amino acids and NE are then highly recommended.

Good agreement of swine performance and NE system have been measured in different studies. Energy retained was positively correlated with NE intake whereas negative or nor correlation were found with DE and ME intake, respectively. They confirm the superiority of the NE system (in comparison with DE or ME systems) for predicting performance and energy gain of pigs and controlling carcass adiposity, especially for feeds with variable crude protein contents.

Easy calculation of NE values for swine

Feed energy content was initially measured on a large number of complete feeds with a large range of nutrient content. These measurements allowed development of predictive equations used to calculate the NE content of raw material based on DE, crude protein, crude fat, crude fiber and starch for vegetable raw material.

In order to democratize the use of these equations among professionals in the sector, Adisseo developed an online tool (called Nestor) to provide NE content for major raw materials. It also provides recommendations for NE for swine, alongside recommendations on digestible amino acids and minerals. These are presented in the online service, based on specific conditions (rearing period, sex, age, breed) that is added by the user. The calculated nutritional values, including NE, can hence be downloaded as PDF or csv file to upload the data in feed formulation software and update the matrix values.

Implementing NE system make significant change in swine feed formula

Moving from ME to NE formulation is associated with change on feed composition and economical savings. This is explained by the difference of RM hierarchy. An evaluation of this migration was performed in grower diet (Table 1). Energy efficiency was improved and NE to ME ratio increased by 0.6 and 0.8 percent unit for grower and finisher, respectively. Using NE system allows also a protein reduction, with less protein meal but more synthetic amino acids on the feed. Economical gain ranges from 5 to 10 €/ton for grower and finisher swine diets, respectively. These values might vary depending on raw material availability and/or price context.

The implementation of NE system is a major step forward from the use of the DE and ME systems. Combined with the use of digestible amino acids, and the right nutritional constraints, NE system allows nutritionists to be closest to the animal performance. Additionally, improving nutrient utilisation and efficiency decreases wastage, meaning that NE is the best system for a more sustainable pig production. So, the momentum is here to start using it actively in swine feed formulation. For a wider adoption of the NE system for swine in regions not already using. NE is simply the most appropriate system.

¹ Price of raw material collected during February 2023 in a French context.

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