Effects of several levels of extracted tannin from grape pomace on intestinal digestibility of soybean meal

Grape pomace (GP) is a high tannin feed by-product produced in large amounts in many parts of the world. Tannins bind to proteins to prevent their degradation in the rumen. This tannin/protein complex may be advantageous when partially protecting high quality feed proteins from excessive rumen protein degradation. The objective of this experiment was to use a GP tannin extract to slow down rumen degradation of soybean meal (SBM) protein. After extracting the tannin compounds, SBM was treated with the extract to obtain mixtures with 0, 15, 30, 40 and 60 g/kg dry matter (DM) of tannin extract. In vitro gas production (IVGP), organic matter digestibility (OMD) and ammonia concentrations were measured, and three rumen-cannulated sheep were used to determine in sacco rumen disappearance of N. A three-step in vitro procedure was used to determine intestinal digestibility. Treating SBM with tannin extract decreased IVGP (linear and quadratic; P < 0.01) by 4.5–11%, and the in sacco digestibility of soluble N fraction (linear and quadratic effects, P < 0.01) by 15–274%. It also delayed gas production (T/2) and increased in vitro intestinal digestibility of protein (linear and quadratic; P < 0.01) by 8.9–17.8. Tannins in GP slow down SBM protein degradation in the rumen.