A Comparison of Total Collection and Index Method Estimates of Energy Values of Full Fat Soybean Using Regressing Method for Growing Pigs

This experiment was conducted to compare total collection (TC) and index method (IM), including chromic oxide (Cr₂O₃), titanium dioxide (TiO₂), and acid insoluble ash (AIA), for determining the energy values of full fat soybean (FFS) using the regression method. Twenty-four barrows with an average initial BW of 20 kg were assigned to 3 diets in a randomized complete block design. The 3 diets consisted of a corn–soybean meal reference diet (RD); the RD + 75 or 150 g/kg FFS, and all diets contained three index markers (5 g/kg Cr₂O₃, 5 g/kg TiO₂, and 20 g/kg AIA). Each diet was fed to 8 barrows in individual metabolism crates for a 5-d acclimation followed by a 5-d total collection of feces and urine separately. All data were analyzed as split-plot experiments, where the FFS level was the main-plot factor and measurement method including TC or IM with different markers was the split-plot factor. Results showed that the fecal marker recovery was 90.0, 90.9, and 93.3% for TiO₂, Cr₂O₃, and AIA, respectively, when compared with total collection. The substitution of FFS linearly reduced (P < 0.05) both dietary DE and ME. With the increase of FFS level, the dietary DE was linearly decreased based on TC, AIA, and TiO₂ measurements, but not for Cr₂O₃, resulting in an FFS level by measurement method for dietary DE (P = 0.056). The results also showed that the determined dietary DE was lower using TiO₂ compared with TC, Cr₂O₃, and AIA (P < 0.05). And the dietary ME determined by TiO₂ was lower than TC and AIA (P < 0.05), but similar with Cr₂O₃. The energy value of FFS was determined by the regression method. The TC-derived DE and ME of FFS were 4131 kcal/kg and 3873 kcal/kg, respectively. The DE and ME of FFS in kcal/kg DM were 4072 and 3814 using Cr₂O₃; 3935 and 3867 using TiO₂; or 3991 and 3734 using AIA. The DE of FFS using TC method was not different from those obtained from Cr₂O₃ and AIA, but higher than the DE value obtained from TiO₂ (P < 0.05). In conclusion, the IM is as robust as TC to derive DE of FFS using the regression method, but the accuracy may be dependent on the marker.