Basis of feed value calculations - Pigs

The energy value of pig feeds is based on net energy (NE) and it is expressed as megajoules per kg dry matter (MJ/kg DM). The equations are based on INRA-AFZ feed evaluation system (EvaPig 2020). The NE values have been calculated using equations of EvaPig® program. The NE values are presented separately for growing pigs (from weaning to live weight of 150 kg) and adult pigs (boars and pregnant and lactating sows).  

The NE values have mainly been calculated based on the reference ingredients of EvaPig® program. Calculation based on reference ingredients is the recommended way as in that case, feed material specific equations and coefficients are used. If suitable reference ingredient cannot be found, the NE value of a feed material has been calculated based on the analysed chemical composition. Calculation based on chemical composition is based on general equations.
For calculating the NE value of a feed material, the following information of the chemical composition is required. If the information is not available, values of the reference ingredient are used. If calculations are based on the chemical composition of the feed material, analysed values for composition are compulsory except for sugars.

• Dry matter
• Ash
• Crude protein
• Fibre: crude fibre (Weende method), NDF or ADF
• Fat: ether extracts
• Starch
• Sugars: increases the accuracy of calculations
• Gross energy: if fat concentration is not available when calculating based on chemical composition

1.  Calculation of NE value based on a reference ingredient

The reference ingredient is chosen so that it resembles the new feed material as well as possible based on its botanical or other source and chemical composition. The calculation will combine the feed value of the reference ingredient and the difference in chemical composition between the reference ingredient and the new fed material using coefficients. The general form of the equation is:
Y_New = Y_Ref + a × (X_New – X_Ref) + b × (Z_New – Z_Ref) + …
where Y is the calculated value, X, Z etc. are the chemical components and a, b etc. the feed material specific or general coefficients. “New” refers to the new feed material and “Ref” to the reference ingredient in the Feed Table of the Evapig® program. The equations, coefficients and ratios of energy values are presented in the Evapig® program Handbook of Equations and Coefficients.
The following steps are included in the calculation of NE values based on reference ingredient (f=function, g = growing pigs, a = adult pigs)

• Gross energy, GE = f(protein, fat, ash)
• Energy digestibility for growing pigs, Ed_g = f(fibre)
• Digestible energy for growing pigs, DE_g = GE × Ed_g
• Digestible energy for adult pigs, DE_a = f(DE_g, Ed_g, ash)
• Ratio of metabolisable energy and digestible energy, ME/DE = f(protein, DE)
• Metabolisable energy, ME = DE × ME/DE
• Ratio of net energy and metabolisable energy, NE/ME = f(protein, fat, strach, ME)
• Net energy, NE = ME × NE/ME.

2.  Calculation of NE value based on chemical composition

If suitable reference ingredient cannot be found from Evapig® program, the NE values for growing and adult pigs are calculated based on the chemical composition of the feed material using the general equations of the program.  This method is not as accurate as the one based on the reference ingredient as it does not take into account feed material specific factors. 

The following steps are included in the calculation of NE values based on chemical composition:

• GE = f(protein, fat, ash, fibre, sugars, starch); Analysed GE value can be used instead of a GE value calculated based on the chemical composition
• Feed material Ed_g = f(fibre); equations including ash concentration should not be used
• DE_g = GE × Ed_g
• DE_m=f(DE_g, Ed_g, ash, protein)
• Energy loss in urine = f(protein)
• Energy loss in methane = f(ash, protein, fat, starch, sugars)
• ME = f(DE, urine energy, methane energy)
• NE = f(DE, protein, fat, starch, fibre).

The following information of pig feeds are included in the Feed Table:

• Standardised ileal digestible lysine, g/kg DM
• Standardised ileal digestible methionine + cysteine, g/kg DM
• Standardised ileal digestible threonine, g/kg DM
• Standardised ileal digestible tryptophan, g/kg DM
• Standardised ileal digestible valine, g/kg DM
• Digestible crude protein for growing pigs, g/kg DM
• Digestible crude protein for adult pigs, g/kg DM

Standardised ileal digestible amino acids are calculated based on Evapig® Feed Table standardized ileal digestibility of amino acids for reference ingredients and the amino acid composition presented in Luke Feed Tables. For feed materials presented in Table 1, the standardised ileal digestibility coefficients of amino acids have been calculated based on in vitro digestibility of nitrogen and dry matter (Boisen & Fernandez 1995) using equations (Boisen 2007).

In Luke Feed Tables, the total tract digestibility of phosphorus is presented according to Evapig® program. Table 2 presents the feed materials for which the digestibility of phosphorus is based on Finnish experiments.