Effects of different processing procedures for rice bran on dietary nutrient digestion in each segment of the digestive tract of steers

Effects of feeding raw, heated and defatted rice brans (RR, HR and DR, respectively) and wheat bran (WB) on in situ rumen dry matter disappearance, the site and extent of digestion of dietary nutrients, and microbial synthesis in the rumen were investigated. Four Holstein steers fitted with ruminal, duodenal and ileal cannulas were used in a 4 × 4 Latin square design. Four diets consisting of 34–38% bran, 40% chopped Italian ryegrass hay and other supplements were formulated to contain 14% crude protein. All diets were fed at the same level of digestible energy intake (1.8 times maintenance requirement). Dry matter disappearance in situ was less for DR than for RR during the 24 h of incubation, but was higher afterwards. Disappearance of dry matter for HR was lower than for RR during the whole incubation period. Real intake of digestible energy was lower for RR and HR diets than for DR and WB diets due to lower than expected digestibility of fiber in the rumen and of fat in the small intestine. The proportion of nonstructural carbohydrates digested in the large intestine and total tract digestibility was higher for the rice bran diets than for the WB diet. Ruminal digestibility of starch was over 90%, but that of nonstructural and nonstarch polysaccharides was less than 40% for all diets. Nitrogen digestibility in the small intestine did not differ among diets, but was highest in the rumen and the total digestive tract for the WB diet. Microbial flow to the duodenum and microbial efficiency did not differ among diets. Raw and heated rice bran diets resulted in a higher proportion of propionate in ruminal fluid than did DR and WB diets. It is concluded that digestion of fiber and energy intake for high rice bran diets is increased by defatting the rice bran, but not by heat processing.