Fecal amylase-treated neutral detergent fiber and ash contents as independent variables can predict metabolizable energy and coefficient of energy digestibility of diets for growing pigs without dietary information

The objectives of the present study were to develop prediction equations for digestible energy (DE), metabolizable energy (ME), and coefficient of energy digestibility (ED) of swine diets using fecal nutrients as independent variables without dietary information and to validate the prediction equations. A total of 262 fecal samples obtained from growing pigs fed 27 diets in 4 experiments were used to develop prediction equations for DE, ME, and ED. These equations were validated using 95 fecal samples obtained from growing pigs fed 12 diets in an additional experiment. The diets were based mainly on corn, soybean meal, and other plant-originated feed ingredients. In the digestibility experiments, feces and urine were quantitatively collected using the marker-to-marker procedure. Diet and fecal samples were analyzed for dry matter (DM), crude protein, ash, and amylase-treated neutral detergent fiber (aNDF). The DE of the 27 diets ranged from 12,164 to 18,301 kJ/kg DM and ME of 24 diets ranged from 11,603 to 16,657 kJ/kg DM. Coefficients of ED for the 27 diets ranged from 0.667 to 0.919. Fecal ash was positively correlated with DE (r = 0.81; P < 0.001), ME (r = 0.66; P < 0.001), and coefficient of ED (r = 0.67; P < 0.001) whereas fecal aNDF was negatively correlated with DE (r = –0.66; P < 0.001), ME (r = –0.74; P < 0.001), and coefficient of ED (r = –0.67; P < 0.001). The prediction equations developed using fecal nutrients were: DE (kJ/kg DM) = 15,077 + (13.72 × ash) – (4.65 × aNDF) (R² = 0.71; P < 0.001); ME (kJ/kg DM) = 17,067 + (6.54 × ash) – (7.56 × aNDF) (R² = 0.63; P < 0.001); and coefficient of ED = 0.881 + (0.00037 × ash) – (0.00028 × aNDF) (R² = 0.57; P < 0.001) where nutrients are expressed as g/kg DM. Based on the regression analysis for validation of the equations, the prediction equations for DE and coefficient of ED using only fecal aNDF did not have mean bias or linear bias. In conclusion, DE values, ME values, and coefficient of ED for swine diets are correlated with fecal ash and aNDF concentrations and the energy values can be predicted using fecal ash and aNDF concentrations without dietary information.