EFFECT OF CHANGING THE PROPORTION, WHEAT SORGHUM IN DAIRY-COW RATIONSON CARBOHYDRATE DIGESTIBILITY AND NAN FLOW TO THE INTESTINE

Five rumen- and abomasum-cannulated cows in mid-lactation were fed ad libitum, for two periods of 21 d each, two isonitrogenous (17% crude p rotein) total mixed rations (TMR) composed of 45% sorghum-wheat combin ation, 38% corn silage, 12% soybean meal, urea, buffers and minerals. The two TMRs differed in their sorghum (S): wheat (W) ratio, which was 70/30 in S and 30/70 in W treatments. Dry matter intake was 17.2 and 16.6 kg d(-1) in S and W, respectively. Effect of treatments on the di gestibility df carbohydrate constituents and N metabolism was examined . Neutral detergent fiber (NDF)-polysaccharides digestibility in stoma chs and the entire gastrointestinal tract (GIT) was significantly high er in S than in W. The digestibility of neutral detergent soluble (NDS )-alpha-glucans was significantly higher in W than in S. More of NDS-a lpha-glucans escaping ruminal fermentation was digested in the intesti ne of the S cows as compared with the W cows. The digestibility in ent ire GIT of total NDS-monosaccharide residues was 93% in W and 86% in S . Digestibility values of total carbohydrates in stomachs (49% and 52% ) and entire GIT (79% and 80%) of S and W cows were similar. S and W c ows were similar in rumen pH (6.15 and 6.13), rumen volatile fatty aci ds concentrations (133 and 136 mM) and rumen NH, concentration (21 and 23 mg per 100 mi). Non-ammonia-N flow through the abomasum (410 and 4 03 g d(-1)) and N absorption in the intestine (67%) were also similar in S and W.