Effect of corn variety and fat supplementation on digestion of diets for feedlot cattle containing dry rolled or steam-flaked corn

Two corn hybrid varieties [normal yellow dent corn (NC) and high oil corn (HOC)] and two levels of supplemental fat (0 vs. 30 g yellow grease/kg diet, YG) were evaluated in two 4 × 4 Latin square experiments involving eight Holstein steers with ruminal and duodenal cannulas. In Experiment 1, corn varieties were processed by dry rolling. In Experiment 2, they were processed by steam flaking. Non fat-supplemented NC and HOC diets contained 2.7 and 4.8 g of fatty acids (FA)/kg diet, respectively. Fat supplementation increased FA content to 4.9 and 7.1 g FA/kg diet for NC and HOC diets, respectively. With dry rolled corn varieties (Experiment 1), there were no treatment interactions on ruminal, postruminal and total tract digestion of OM, starch and N. There were interactions (P≤0.05) between corn variety and supplemental YG on ruminal aNDFom and postruminal FA digestion. With dry rolled NC, supplemental YG decreased ruminal aNDFom digestion, and postruminal FA digestion. Whereas, with dry rolled HOC, supplemental YG increased ruminal aNDFom digestion, but did not affect postruminal FA digestion. YG decreased (P<0.01) ruminal digestion of OM (11%) and starch (10%). Supplemental YG did not affect (P>0.05) total tract digestion of OM, starch, aNDFom and N, but increased (2.5%, P≤0.05) dietary DE. Ruminal (P<0.01) and total tract digestion (P≤0.05) of OM (1.4 and 3.0%) and starch (11.2 and 2.3%) were greater for NC vs. HOC diets. Likewise, ruminal aNDFom digestion tended to be greater (11.2%, P=0.07) for NC vs. HOC diets. Corn variety did not affect (P≥0.55) postruminal digestion of OM, starch and N. Corn variety did not affect (P≥0.53) total tract digestion of N, aNDFom or DE diet. With steam-flaked corn varieties (Experiment 2), there were no treatment interactions (P>0.05) on ruminal, postruminal and total tract digestion of OM, aNDFom, starch and N. There were interactions (P≤0.05) between corn variety and supplemental YG on intestinal FA digestion. With the NC diets, YG decreased FA digestion; whereas with the HOC diets, supplemental YG increased FA digestion. Supplemental YG did not affect (P>0.05) ruminal digestion, postruminal, or total tract digestion of OM, aNDFom, starch, N. Diet DE value was greater (3.1%, P≤0.05) for YG supplemented diets. There were no corn variety effects (P>0.05) on ruminal, postruminal and total tract digestion of OM, aNDFom, starch and N. Postruminal FA digestion was greater (6.7%, P<0.01) for NC than for HOC. It is concluded that the feeding value of high oil corn may not be different from that of normal corn. Independent of processing, the greater initial energy density of high oil corn is offset by slightly lower OM and/or fatty acid digestion.