Effects of tannins and drying methods on in vitro dry matter and crude protein degradability and digestibility in rapeseed meal

The extensive ruminal degradability of rapeseed meal limits its efficiency as a protein source in ruminant diets by reducing the proportion of dietary protein available for post-ruminal absorption. This study, conducted entirely in vitro, investigated the interactive effects of two tannin types: chestnut water extract (CWE) and quebracho extract (QUE), two tannin inclusion levels (50 or 100 g/kg), and three drying methods (freeze-drying, oven drying at 50 °C or 80 °C) on the in vitro dry matter and crude protein degradability and digestibility of rapeseed meal. In vitro assessments were conducted using rumen fluid from cannulated rams and a three-step enzymatic procedure. A three-way linear model including tannin type, concentration, drying method and their interactions was used. In vitro crude protein degradability decreased by 128 and 243 g/kg dry matter when 50 and 100 g chestnut/kg were included and dried at 50 °C, respectively. By-pass protein content increased by 105 and 219 g/kg dry matter with included 50 g CWE/kg and 100 g QUE/kg dried at 50 °C, respectively. Notably, the combination of 100 g CWE/kg and 80 °C drying significantly reduced in vitro crude protein digestibility by 50 g/kg dry matter. At 80 °C drying, in vitro dry matter degradability reduced the most, by 237 and 366 g/kg dry matter at added 100 g QUE and CWE/kg, respectively. Overall, the application of tannins with drying at 50 °C or 80 °C can improve the amount of by-pass protein in rapeseed meal. These findings indicate a potential for novel tannin-processing strategies of rapeseed meal in ruminant nutrition.