Effect of tannins and drying methods on in vitro dry matter and crude protein degradability and digestibility of soybean meal for ruminants

Soybean meal is a widely used protein source for ruminants, but its high ruminal degradability can limit its nutritional value. Tannins reduce ruminal crude protein degradability by forming tannin-protein complexes, which are facilitated by water addition and heat during drying. The study evaluated the effects of drying methods (freeze-dried, 50 °C, 80 °C) combined with two tannin types (chestnut and quebracho) at two concentrations (50 and 100 g/kg) on the in vitro degradability and digestibility of soybean meal dry matter and crude protein. Tannins combined with drying methods effectively reduced ruminal degradation of soybean meal protein. The drying at 80 °C combined with chestnut or quebracho tannins at both concentrations (except 100 g/kg chestnut tannins) showed the largest reduction in ruminal crude protein degradability without negatively affecting post-ruminal digestibility. The most effective combination for reducing crude protein (-42.3%) degradability compared to the control was 50 g/kg chestnut tannins with drying at 80 °C without affecting in vitro dry matter and crude protein digestibility. This combination also increased by-pass protein content (431 g/kg DM) and improved its digestibility by 21%.