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.
Highlights
The rate of live weight gain (LWG) in growing cattle is usually improved by the inclusion of concentrates in grass silage diets owing to the increased energy intake (Thomas et al 1988,Lampila and Micordia 1990)
The rumen degradability of protein was similar in rapeseed meal (RSM)-based and in meat and bone meal (MBM)-based concentrates (Table 2), whereas both in silage and barley it was higher than in RSM-based and MBM-based concentrates
The decreased ruminal pH resulting from concentrate supplementation was found in the present study to be related to the higher total volatile fatty acids (VFA) concentrations in the rumen
Summary
The rate of live weight gain (LWG) in growing cattle is usually improved by the inclusion of concentrates in grass silage diets owing to the increased energy intake (Thomas et al 1988,Lampila and Micordia 1990). The improved LWG may have been related either to an increased uptake ofamino acids or to improved digestibility of the diet and thereby increased feed intake. In regard to grass silage intake, somewhat contradictory results have been obtained. Huhtanen et al (1985), Steen (1988), Aronen (1990) and Moloney (1991) did not find any changes in voluntary grass silage intake when pro-.
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