The effect of supplementing highly wilted grass silage with maize silage, fodder beet or molasses on degradation of the diets and the efficiency of microbial protein synthesis in the rumen of sheep

This study aimed at determining the efficiency of microbial protein synthesis (EMPS) in diets based on highly wilted grass silage [(GS) 539 g dry matter (DM) kg-1] with the supplementation of starch or water-soluble carbohydrates (WSC) rich feeds, i.e. maize silage [MS, 391 g kg-1 DM intake (DMI)], fodder beet (FB, 173 g kg-1 DMI) or molasses (M, 137 g kg-1 DMI). All the diets were made isonitrogenous by urea supplementation (14.0, 4.0 and 2.0 g kg-1 DMI in GS-MS, GS-FB and GS-M diets). In sacco determined crude protein (CP) and organic matter (OM) degradabilities were 756, 800, 778 and 814 (P<0.05) and 563, 577, 593 and 618 g kg-1 (P<0.05) in GS, GS-MS, GS-FB and GS-M diets, respectively. Synchrony indexes that describe the synchrony of CP and OM degradation in the rumen were 0.75, 0.67, 0.67 and 0.79 in GS, GS-MS, GS-FB and GS-M diets, respectively. The EMPS, assessed by means of urinary purine derivative excretion, did not differ significantly (P>0.05) among the diets (36.6, 35.1, 34.7 and 34.0 g microbial nitrogen kg-1 OM apparently digested in the rumen in GS, GS-MS, GS-FB and GS-M diets, respectively). The estimated metabolizable protein supply from GS, GS-MS, GS-FB and GS-M diets amounted to 98, 90, 93 and 87 g kg-1 DMI, respectively. Apparently, highly wilted GS containing a high concentration of WSC (91 g kg-1 DM) supports high EMPS in the rumen and this cannot be improved by the supplementation with starch or water-soluble carbohydrates (WSC) rich feeds.