Ruminal and Post-Ruminal Utilization of Nitrogen and Starch from Sorghum Grain-, Corn- and Barley-Based Diets by Beef Steers

Abstract

Sorghum grain-, corn- and barley-based diets (approximately 82% grain) were fed to six ab-omasal-fistulated steers (avg. weight 448 kg) in a replicated 3 × 3 Latin-square design to determine ruminal, post-ruminal and total tract utilization of N and starch, and extent of bacterial protein synthesis. Each trial included a 6-d period of total fecal collection and abomasal sampling (12-h interval advanced 2 h daily). Mean daily intakes of organic matter (OM) and N were equalized among treatments. Although percent digestibility of OM was not different (P>.05) among diets, total tract digestibility of N and starch were lower (P<.05) for the sorghum grain diet than for the corn and barley diets. Ruminal digestibility of starch for the sorghum grain diet was lower (P<.05) than for the corn and barley diets (75 vs 84 and 88%, respectively). Even though there was a lower (P<.05) post-ruminal digestibility coefficient of starch for the sorghum grain diet, more (P<.05) abomasal starch (g/d) was digested post-ruminally for the sorghum grain diet than for the barley diet. The amount of non-ammonia N reaching the abomasum and the post-ruminal digestibility of N were not different (P<.05) among diets. The percentage of bacterial N in the abomasum was higher (P<.05) for the barley diet than for sorghum grain and corn diets (72 vs 47 and 53%, respectively). The percentage of undegraded feed N in the abomasum for the sorghum grain and corn diets was approximately twice as high as that for steers fed the barley diet. The amount of starch and source of amino acids available for post-ruminal digestion differs markedly among these feed grains. The lower apparent total tract digestibility of sorghum grain protein and starch appears to be related to the extent of feed degradation in the rumen.