Optimizing dietary protein utilization is essential for improving ruminant nutrition, and tannins can reduce the ruminal degradability of soybean meal (SBM) proteins through tannin–protein complex formation, a process enhanced by water. This study evaluated three water levels (1:0.625, 1:1.25, 1:2.5 w/v) combined with chestnut or quebracho tannins at 50 and 100 g/kg on in vitro dry matter (DM) and crude protein (CP) degradability and digestibility of SBM. Increasing water levels significantly reduced crude protein degradability (p < 0.05), with the greatest decline observed for chestnut tannins at 100 g/kg, decreasing from 640 g/kg at the lowest water level to 423 g/kg at the highest. Post-ruminal crude protein digestibility increased slightly with water for this treatment (from 977 to 984 g/kg). Bypass protein content ranged from 138 g/kg (quebracho 100 g/kg, low water) to 563 g/kg (chestnut 100 g/kg, high water), with increases of 20.7% and 22.6% for chestnut tannins at 50 and 100 g/kg, respectively. Bypass protein digestibility improved by up to 4.4%. Dry-matter degradability decreased by 6.8% to 23.5% depending on treatment. These findings demonstrate that water greatly enhances tannin efficacy and highlight its potential for improving protein utilization.
Valcl et al. (Wed,) studied this question.