Energy values of fiber-rich ingredients with different solubility estimated by different evaluation methods in growing pigs

Abstract

The objectives of this study were to test whether the time-based total fecal collection (TC) method or the index method (IM) using acid-insoluble ash could obtain similar energy values as the reference (RF) method (TC method with marker-to-marker collection procedure) for growing pigs fed fiber-rich ingredients with different solubility. A total of 24 barrows (initial body weight, 33.3 ± 3.4 kg) were assigned to 4 diets and each diet was fed to 6 pigs. Experimental diets included a corn-soybean meal basal diet and 3 fiber-rich diets which were formulated by replacing corn, soybean meal, and soybean oil in the basal diet with 200 g/kg defatted rice bran (DFRB), soybean hulls (SBH), and sugar beet pulp (SBP), respectively. All diets were formulated to contain 10 g/kg celite as a source of acid-insoluble ash to estimate the energy values by the IM method. Each group of pigs was adapted to diets and crates for 7 d, then followed by 5-d feces and urine collections using the time-based procedure and 5-d feces collection using the marker-to-marker procedure, then the same portion of fecal sample collected by the time-based TC method and the RF method for individual pigs were composited into a sample for the IM method. The results showed that the energy values and nutrients digestibility coefficients of each diet estimated by the time-based TC method agreed with the values estimated by the RF method; the IM method with acid-insoluble ash underestimated the energy values and nutrients digestibility coefficients of the SBH diet and the SBP diet compared with the RF method (P < 0.05); there no differences in energy values of fiber-rich ingredients with different solubility between the RF method and the time-based TC method, however, the IM method with acid-insoluble ash underestimated the energy values of SBH and SBP compared with the RF method or the time-based TC method (P < 0.05). In conclusion, results of this experiment indicated the RF method and the time-based TC method may be used to determine energy values for fiber-rich ingredients with different solubility. However, the IM method with acid-insoluble ash may underestimate the energy values and nutrient digestibility coefficients of some fiber-rich diets and ingredients.