Effect of concentrate supplementation to grass silage diets on rumen fermentation, diet digestion and microbial protein synthesis in growing heifers

Abstract

A 4 x 4 latin square experiment was carried out with four growing heifers, each with a rumen cannula and a simple T-cannula inserted in the proximal duodenum. The purpose was to study the effects of the supplementation of concentrate to grass silage on rumen fermentation, microbial protein synthesis and digestion of organic matter (OM), fibre components and N. The diets were composed of grass silage alone (S); grass silage and barley (SBU, 50:50 % on dry matter (DM) basis); and grass silage, barley and protein concentrate based either on rapeseed meal (SBR), or meat and bone meal (SBM) (50:40:10). To make the diets isonitrogenous, 23 g of urea was given with the SBU diet. The supplementation of concentrates, irrespective of their type, increased the average rumen ammonia-N and total concentration of volatile fatty acids (VFA) and decreased the molar proportion of acetate. Inclusion of concentrates in the diet had a negative effect on the digestibility of cell wall constituents. The production of microbial protein and the efficiency of microbial protein synthesis were not affected by the diet. It appears, therefore, that the supply of nitrogenous constituents for rumen microbes through ruminally degraded protein was adequate in silage feeding, and that no extra benefit, at the utilized level of application, was gained by the supplementation of any of the concentrates.