Silage additives to reduce protein degradation during ensiling and evaluation of in vitro ruminal nitrogen degradability

Despite the high degradability of their proteins, grass and legume silages represent an important option to reach more sustainable livestock systems. To improve the nitrogen use efficiency of these crops, this study assessed the potential of several additives (chestnut tannins, oak tannins, zeolite, erythritol by-product solution and wood molasses) to reduce proteolysis in the silo and in vitro nitrogen degradability. Ryegrass (Lolium multiflorum) and red clover (Trifolium pratense) were ensiled in varying proportions in laboratory-scale silos made of vacuum-packed plastic bags. Dry-matter content, chemical composition, pH, ammonia and volatile fatty acids content were analysed after 34 days of ensiling. Ruminal nitrogen degradability was assessed in vitro (Aufrère & Cartailler, 1988). We observed that the proportion of ammonia in silage was reduced by the addition of oak tannin (−12%) and zeolite (−16%). The addition of zeolite lowered in vitro organic matter digestibility. Rapidly degradable nitrogen (1-hr degradability) was reduced in vitro by both tannins (−6.8% for chestnut and −6.6% for oak) and zeolite (−5.8%), but total degradable nitrogen (24-hr degradability) was only reduced by oak (−6.5%) and chestnut tannins (−7.3%). It suggests that tannins protected proteins from plant and bacterial enzymes by forming a complex that better resists silage fermentations and in vitro protease action. The reduction effects on proteolysis in the silo and on in vitro ruminal nitrogen degradability are limited individually but could be cumulative. Erythritol by-product solution and wood molasses had no effect on silo or in vitro proteolysis.