The energy value of a feed (ingredient or diet) can be expressed as digestible energy (DE), metabolizable energy (ME) and net energy (NE) (Noblet et al., 2005). Research has shown that net energy is the best estimator of the true energy value of ingredients and complete feeds (Noblet et al., 2003; 2005; 2006) as DE and ME underestimate the energy value of feeds rich in fat and starch and overestimate that of feeds rich in protein and fibre. The NE system is also better for predicting animal performance and carcass quality, particularly when pigs are fed low-protein or high-fat diets. For that reason, using net energy for ingredients and for feed formulation is highly recommended.
EvaPig® also provides DE, ME values and NE values. These values were derived from literature data and calculated as follows:
As research from INRAE showed that live weight and feeding level influence the digestibility of energy and nutrients, separate values are given for the growing pig (from weaning up to 150 kg) and the adult pig (boar, gestating sow and lactating sow).
Finally, the contributions of the ingredients are considered to be additive when included in a complete diet, assuming that vitamins and minerals supplements have a zero energy value.
The energy values provided in the table refer to mashed ingredients. However, technological processes such as intensive grinding, pelleting and extrusion, or the addition of substances such as enzymes, are known to increase energy digestibility. The increase depends on the ingredient and on the nature of the process. It is mostly noticeable in the growing pig and is supposed to be less important in the adult pig (although no literature data is yet available). EvaPig® makes it possible to take into account the effect of technology by applying an “energy bonus” that can add up to 5% to the energy values. This bonus can also be used when the energy value of the reference ingredient seems underestimated. Likewise, a negative value can be used when the reference data seem overestimated. This correction is applied to the DE value and consequently modifies the ME and NE values, both for the growing and the adult pig.
Similarly, it is possible to use an “energy bonus” for diets (positive bonus only) that have undergone a technological process. For instance, pelleting increases digestibility by 1 to 3 points for diets based on wheat, maize or soybean meal. In EvaPig®, it is possible to add a different bonus to growing and adult pigs, as the effect of technology is supposed to be small or insignificant in the latter case. Note that one should not use at the same time an energy bonus for a diet and individual energy bonuses for its constitutive ingredients. Also, the energy values for ingredients such as rapeseeds or linseeds are already provided for processed materials since the raw, unprocessed ingredients (and particularly their lipid fraction) have a low digestibility: for those ingredients, adding a bonus to the reference data is not required.
Protein value can be assessed through the digestibility of the protein itself or, more accurately, through the digestibility of its individual amino acids. There are several methods to determine these digestibility values: they can be measured at faecal or ileum level, and they can be corrected (standardised, real) or not (apparent) for the different types of endogenous losses.
EvaPig® provides values of ileal standardised digestibility of amino acids. This system is currently the most elaborate for protein value, with data being available for all common ingredients. The digestible amino acid value is corrected (standardised) for basal endogenous losses of amino acids unrelated to the feed protein and supposed to be proportional to the dry matter intake (Noblet et al., 2002; Stein et al., 2007). The standardised ileal amino acid digestibility coefficients for ingredients provided with EvaPig® originate from a series of in vivo experiments carried out in France by INRAE, Adisseo, Arvalis (with Ajinomoto Animal Nutrition Europe) in the years 1980-2000. These data were collected and processed into table values, first published as a CD-Rom (AmiPig, 2000), and later in the INRA-AFZ tables (Sauvant et al., 2002; 2004).
The ileal standardised digestibilities of amino acids provided for the reference ingredients in EvaPig® are theoretically independent from the amount of feed protein. The standardised digestible amino acids of diets ingredients are assumed to be additive. Unlike energy digestibility, ileal digestibilities of amino acids are supposed to be identical for all stages of pig production and there is insufficient literature data to take into account the effects of technological processes.
For ingredients without known ileal digestibilities of amino acids, missing values have been replaced by average digestibility coefficients obtained by INRAE on a large number of diets.
The ideal protein is defined as one that provides the exact balance of amino acids needed for optimum performance. To make the best use of this concept, EvaPig® also expresses digestible amino acids as a percentage of digestible lysine (Dourmad et al., 2008; van Milgen et al., 2008). The amino acid balance being a good indicator of the equilibrium between amino acid intake and requirements, digestible amino acid content in diets is also expressed relatively to the content in digestible lysine.
EvaPig® provides and calculates the faecal digestibility of nitrogen for ingredients and diets. Though of little interest for assessing the protein value, it is useful for estimating the breakdown of nitrogen output between faecal and urinary pathways.
EvaPig® contains reference data for total and digestible phosphorus content, mostly derived from the INRAE-CIRAD-AFZ Tables.
When EvaPig® calculates the digestible apparent phosphorus content of a diet, it takes into account the effect of endogenous phytase (if still active in a mash form for instance) and added (exogenous) phytase. The effects of added and endogenous phytase are additive. Endogenous phytase is used in the calculations when the diet includes ingredients with notable phytase activity, such as rye, wheat and their by-products, and when the diet does not undergo a technological process such as pelleting.
The effect of phytase on the release of phytic phosphorus is supposed to be curvilinear, with a marginal effect that decreases when the amount of exogenous phytase increases (Jondreville and Dourmad, 2005). The biological activity of the added phytase, calculated as the amount of digestible P released per 500 IU of phytase, is required in the calculations. Typical phytase activity ranges from 0.5 to 0.9 g per 500 IU of phytase.
Note: the equations and coefficients used in EvaPig® will be provided in full detail on the EvaPig® website.
EvaPig® uses equations to calculate the nutritional values of new ingredients and diets. These equations were obtained through INRAE experiments or derived from literature data.
The main benefit of using equations is that the predicted values are more precise than fixed values. However, this precision depends on many factors, not all of which are known, and users should always exercise caution when using predicted values.
When calculating the energy value or amino acid and phosphorus digestibility of an ingredient that derived from a reference ingredient, EvaPig® uses for the new ingredient a combination of generic equations and specific equations. For instance, gross energy is predicted using a generic equation requiring protein, fat and ash with coefficients that are identical for all ingredients; on the other hand, energy digestibility is predicted from fibre content with coefficients specific to the ingredient (botanical species, type of process…).
The calculations consist in combining the nutritional value of the reference ingredient and coefficients that are applied to the differences in chemical composition between the new ingredient and the reference ingredient. The formula takes the following general form:
Y New = Y Reference + a x (X New – X Reference) + b x (Z New – Z Reference) + …
where Y is the predicted value and X, Z etc. are the predictors. “New” refers to the new ingredient and “Reference” refers to the reference ingredient.
For instance, the calculations of energy values involve the following steps:
EvaPig® can calculate nutritional values of new ingredients and diets from their chemical composition only. For energy values, the calculation process predicts gross energy, energy digestibility, ME and NE using generic equations based on chemical composition (and on in vitro organic matter digestibility, in the case of diets).
Ingredients and diets should be created using chemical composition only when no other option is available, but users should be aware that the generic equations used in the calculations are less precise and fail to take into account ingredient-specific effects such as anti-nutritional factors or the structure of cell walls.
For diets created from a list of ingredients, the chemical and nutritional values are calculated as the weighed contributions of the ingredients, taking into account their incorporation rates and dry matter values.
When a nutrient is missing from an ingredient, it will not be part of the diet calculations: for instance, if an ingredient does not have a net energy value attached, net energy will not be calculated for any diet including this ingredient.
The calculations are more complex for phosphorus digestibility:
To efficiently use the nutritional values proposed by EvaPig®, adaptations of both diet characteristics and animal requirements may be necessary. EvaPig® provides specific diet criteria to help users to meet those requirements.