The present experiment was conducted to assess the effects of rice straw supplemented with soybean meal (RSS-diet) on turnover rate of plasma acetate using an isotope dilution method in sheep. Rumen fermentation characteristics and nitrogen (N) balance were also determined. Four sheep were assigned to two dietary treatments including either a RSS-diet or mixed hay (MH-diet). The experiment was performed by a crossover design with two 24 day periods. On day 24 of each dietary period the isotope dilution method of [1-13C]Na acetate was carried out as the primed-continuous infusion to determine the plasma acetate turnover rate. Nitrogen intake and N retention did not differ between diets, while N digestibility was higher (P = 0.004) for the RSS-diet than the MH-diet. Concentrations of rumen total volatile fatty acid (VFA) and acetate did not differ between diets, and those of other individual VFA were higher (P < 0.05) for the RSS-diet than the MH-diet. Concentration and turnover rate of plasma acetate did not differ between dietary treatments. From the present results it could be concluded that rice straw supplemented with soybean meal as high energy protein source showed the comparable performance to mixed hay on plasma acetate turnover rate, and enhanced performance over mixed hay on digestive functions in sheep.
Acetate metabolism, isotope dilution, rice straw, soybean meal, sheep.