Evaluation of linseed meal for dairy cows: Interaction with grain source on forestomach and whole-tract digestion

Abstract

Four Holstein cows in midlactation were fed one of four totally mixed rations differing in grain source (ground barley or cracked corn) and protein meal (solvent-extracted linseed meal or canola meal) in a 12-wk 4 × 4 Latin square experiment. Diets were 10% second-cut alfalfa silage, 50% whole crop oat silage and 40% mixed concentrate on a DM basis. Intake of DM, OM, NDF, starch and crude protein were not influenced by grain source or protein source within grain. Forestomach and whole-tract digestion of these same components were not influenced by treatments, except forestomach digestion of starch which was higher on barley versus corn based diets. Rumen pool sizes of total ingesta DM OM, and NDF were not influenced by treatment, although the rumen pool of NDF tended (P = 0.10) to be higher on barley-based diets. The rumen NAN pool was higher on barley-based diets and this primarily reflected a numerically higher bacterial N pool. Duodenal flow of NAN, bacterial N, residual N and AA protein were also unaffected by treatment although the AA profile of duodenal protein was influenced by both grain source in the diet and source of protein within grain source. Based upon all these results, solvent extracted linseed and canola meals appear to be broadly equivalent as high DIP sources for dairy cows. In addition, animal protein status calculations suggest that the performance of the cows was limited by supplies of DIP on all diets indicating that linseed and canola meals were truly equal as high DIP protein sources for dairy cows. Key words: Canola meal, linseed meal, amino acid, duodenum