Effect of Water Level and Tannin Inclusion on In Vitro Degradability and Digestibility of Soybean Meal

TL;DR

This study shows that adding water and tannins to soybean meal can reduce protein breakdown in the rumen, making more protein available for digestion later.

Contribution

The study demonstrates that water significantly enhances the effectiveness of tannins in reducing rumen protein degradability.

Findings

Higher water levels reduced rumen protein degradation and increased post-ruminal protein availability.

Chestnut tannins at 100 g/kg with high water reduced crude protein degradability from 640 to 423 g/kg.

Bypass protein content increased up to 563 g/kg with chestnut tannins at high water levels.

Abstract

Efficient use of dietary protein is necessary for healthy and sustainable ruminant production. Soybean meal is a common protein source for ruminants, but it is broken down too quickly in the rumen, leading to nitrogen losses for the animal. One way to offset this effect is with the addition of tannins, which bind protein making them less degradable in the rumen. The binding process is affected by water. The aim of this study was to assess the effects of low, medium and high water levels combined with two tannins, added at two concentrations on the in vitro degradability and digestibility of dry matter and crude protein in soybean meal. The results indicate that higher water levels effectively reduce rumen protein degradation and increase protein available for post-ruminal digestion, with no effect on its digestibility, regardless of tannin type or concentration. Rumen degradation of dry matter was reduced as water and tannins increased, which could negatively affect short-chain fatty acid production, rumen microbiota and consequently rumen fermentation. Overall, optimizing water and tannin levels during feed processing may improve the supply of usable protein to ruminants, but fermentation impacts need further research.

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.

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