THE EFFECTS OF FORAGE PRESERVATION METHOD AND PROPORTION OF CONCENTRATE ON NITROGEN DIGESTION AND RUMEN FERMENTATION IN CATTLE

A 6 x 6 Latin square experiment with a 2 x 3 factorial arrangement of treatments was used to study forage preservation method and level of c oncentrate in a diet on organic matter (OM) and N digestion and rumen fermentation. Six bulls, each fitted with ruminal and duodenal cannula e, were given unwilted silage (S) or barndried grass (G) prepared simu ltaneously from the same timothy sward. The forages were fed together with 250 (L), 500 (M) or 750 (H) g concentrate dry matter (DM) kg-1 to tal diet DM. The concentrate consisted of barley (875 g kg-1) and rape seed meal (125 g kg-1). The feeding level was 80 g DM kg-1 live weight 0.75. The apparent digestibility of OM was similar for S and G diets, and increased linearly (P < 0.001) with increasing level of concentra te. The flow of microbial N at the duodenum and the apparent efficienc y of microbial protein synthesis in the rumen were higher (P < 0-05) w ith S than with G diets. Increasing the concentrate level increased li nearly (P < 0.05) the amounts of total N and microbial N at the duoden um, whereas the synthetic efficiency was not significantly affected. T he mean rumen pH decreased linearly (P < 0.001) from 6.43 to 6.03 with increasing concentrate level. The molar proportion of acetate (Ac) in the rumen volatile fatty acids (VFA) showed a linear (P < 0.001) and quadratic (P < 0.01) decrease, and that of butyrate (Bu) a linear (P < 0-001) increase when the level of concentrate was increased. The prop ortion of propionate decreased slightly with both forages when the amo unt of concentrate was increased from level L to M. A further increase to level H increased propionate from 157 to 170 mmol mol-1 of total V FA with S and from 157 to 188 mmol mol-1 with G, the effect of concent rate level being not significant. The number of protozoa increased lin early (P < 0.001) as the level of concentrate increased. The changes i n the rumen fermentation patterns during the feeding cycle were greate r for S than for G diets.