Effects of urea treatment of potato pulp and inclusion levels of potato pulp silage in supplements on digestibility and ruminal fermentation in beef steers

Six Wagyu (Japanese Black) steers fitted with a ruminal cannula were used in a split-plot design experiment comprising a 3 x 3 Latin square design (whole plot) and a randomized blocks design (subplot) to determine the effect of the treatment of potato pulp (PP) with urea and the effect of inclusion levels of PP silage in feed supplement on digestibility, ruminal in situ degradation and ruminal fermentation. The whole plot consisted of 20%, 50% and 80% PP silage (dry matter (DM) basis), with PP silage replacing formula feed. The subplot included untreated or 0.5% (on an as-fed basis) urea-treated PP. The treatment of PP with urea showed no effect on DM intake and digestibility. The percentage of the rapidly degradable DM fraction of the urea-treated PP silage was higher (P0.01) and the percentage of its slowly degradable DM fraction was lower (P0.01) than for the untreated PP silage. Ruminal ammonia concentration was greater (P0.01) for steers fed urea-treated PP silage than that for steers fed the untreated PP silage. The treatment of PP with urea caused a decrease in the molar proportion of acetate and an increase in the proportion of propionate in ruminal fluid after feeding. The rate of DM degradations in hay (linear, P0.01) and in PP silage decreased (linear, P0.01) as the inclusion level of PP silage increased. Increasing the inclusion level of PP silage in supplement decreased the effective degradability of DM in hay (linear, P0.05) and in PP silage (linear, P0.05). An increase in the amount of PP silage increased the molar proportion of acetate (linear, P0.01) and decreased the butyrate proportion (linear, P0.05) in ruminal fluid. The results suggest that urea treatment of PP facilitates microbial access to starch of PP silage in the rumen and that surplus level of PP silage in supplement have adverse effect on ruminal digestion.