Corn Particle Size Mixtures, Roughage Level and Starch Utilization in Finishing Steers Diets

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Abstract
Mixtures of whole and processed corn grain were evaluated in two feedlot-finishing and one digestion experiment. In each feedlot experiment, 60 crossbred steers were individually fed whole shelled corn (W), cracked corn (C), fine ground corn (F), a 50:50 mixture of whole and cracked corn (W-C), or a 50:50 mixture of whole and fine ground corn (W-F) at three levels of chopped alfalfa-brome hay (5,10 and 15% of the diet dry matter). No interactions (P>.05) were observed between corn particle size and roughage level for final weight, daily gain, dry matter intake or dry matter conversion. Dry matter intake increased linearly (P = .002) and efficiency of gain decreased (P = .04) as roughage level in the diet increased. Steers fed the W-C mixture gained more efficiently than steers fed the W (P = .03) or the C (P = .08) diet, while steers fed mixtures of whole and processed corn had faster rates of gain (W vs W-C, P = .007; W vs W-F, P = .02) and heavier final weights (W vs W-C, P = .03; W vs W-F, P = .04) than steers fed diets containing whole corn alone. Fecal starch percentage and fecal pH were not influenced by corn particle size. Fecal starch decreased linearly (P = .03) as roughage level in the diet increased. A negative relationship between fecal starch and fecal pH (r = -.42, n = 60) was observed. However, neither fecal starch nor fecal pH were highly correlated to animal performance. A replicated 3x3 Latin square design was used to evaluate site and extent of digestion of steers fed (ad libitum) diets consisting of whole shelled corn (W), cracked corn (C) and a 50:50 mixture of whole and cracked corn (W-C). Corn particle size did not affect (P>.05) the percentage or the amount of starch digested ruminally or postruminally, but, total tract starch digestion was greater (P = .08) for the C diet than for the W diet. The digestibility of starch subjected to postruminal digestion was similar among corn particle size treatments. Results from these studies indicate that feeding mixtures of whole and processed corn may improve animal performance, but that the improvement cannot be sufficiently explained by optimizing the site or extent of digestion. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science.