Effect of Wilting and Lactic Acid Bacteria Inoculant On in situ and in vitro Determined Protein Value of Grass Silages

Abstract The objective of this study was to evaluate the effect of dry matter (DM) concentration and the use of lactic acid bacteria (LAB) inoculant on the protein value of grass silages. Grass samples containing 170 g DM/kg fresh material were wilted to different DM concentrations (310, 390, 420, 470, 530, 580, 600 g/kg fresh material) before ensiling. Half of the grass material at respective DM was treated with LAB, the other half remained untreated (control, CON). Ruminal degradation of organic matter (OM) and crude protein (CP) was determined using the in situ technique. For this, silage samples were incubated for 2, 4, 8, 16, 24, 48 and 72 h. Rumen undegraded CP (RUCP) was derived from in situ CP degradation. Microbial CP (MCP) synthesis was assumed to be 181 g per kg fermented OM. Post-ruminal CP (prCP) was defined as the sum of RUCP and MCP. Effective prCP in situ (prCPk in situ) was calculated for passage rates (k) of 0.02, 0.04 and 0.06/h. In addition, the modified Hohenheim gas test (modHGT) was used to determine effective prCP in vitro (prCPk in vitro) for the same passage rates. The DM linearly increased prCPk in situ in CON (P