Digestibility of raw soybeans in extruded diets for dogs determined by different methods

Abstract

The objective was to evaluate the coefficients of total tract apparent digestibility (CTTAD) and metabolisable energy (ME) of raw soybeans (RSB) in extruded diets for dogs by three methods (difference, regression and substitution). We also evaluated the urease and trypsin inhibitor (TI) activity, CTTAD, ME and faecal characteristics of adult dogs fed diets containing increasing RSB levels. Six dogs, distributed in a 6 × 6 Latin square design, were fed extruded diets containing 0, 60, 120, 180, 240 or 300 g of RSB/kg. Urease and TI were reduced in all diets after extrusion (p < .01), but TI was not completely inactivated. The inclusion of RSB linearly reduced (p < .01) the digestibility of dry matter (DM), organic matter and crude protein (CP) and linearly increased (p < .05) the digestibility of fat and gross energy and the ME of diets. The CTTAD of DM, CP and fat, and ME of RSB, predicted by the substitution method were: 0.767, 0.758, 0.960 and 20.7 MJ/kg, respectively. The dietary inclusion of RSB reduced faecal DM content and promoted a quadratic increase (p < .01) of pH and ammonia. Increasing RSB in diet reduced CTTAD estimate errors (p < .05). When 300 g of RSB were added per kg of diet, CTTAD of RSB estimated by the three methods did not differ (p>.05). The three methods can be used to determine RSB digestibility. Diet extrusion may not be able to completely deactivate the protease inhibitors present in the RSB. Highlights Extrusion may not be able to deactivate protease inhibitors of raw soybeans. Raw soybeans reduce nutrient digestibility of extruded diets in dogs. The substitution method is recommended to evaluate digestibility of raw soybeans.