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Influence of Degree of Micronization on the Site and Extent of Sorghum Starch Digestion in Beef Cattle Fed High Concentrate Rations¹

Oklahoma Agricultural Experiment Station^,4 Stillwater, Oklahoma 74074

Abstract

High concentrate rations containing sorghum processed by dry rolling or micronizing were fed to steers fitted with permanent rumen and abomasal cannulas. Degree of micronization of the sorghum was varied to produce products with densities of 412, 322 and 232 g per liter. Automatic feeding devices designed to feed 24 times daily were used to create steady state conditions in the digestive tract. No significant differences in the amount of starch digested per day in the rumen were found. Only 51% of the starch entering the intestine from dry rolled sorghum was digested compared to 95% for micronized sorghum (P < .05), suggesting that raw starch from dry rolled sorghum has a reduced susceptibility to enzymatic attack in the small intestine. Ruminal digestion of starch tended to be higher at the higher degree of micronization but degree of micronization had little influence on intestinal and total digestion of starch.

The 12-hr. in vitro dry matter disappearance increased significantly (P < .05) from 41% for dry rolled sorghum to 56% as the degree of micronization increased. Concomitantly, the degree of gelatinization increased from 9 mg maltose/g for dry rolled to 112 mg/g for the high degree of micronization. A narrower ratio of acetate to propionate and a greater total concentration of volatile fatty acids were observed in rumen fluid from steers fed micronized sorghum than in those fed dry rolled sorghum.

¹ Journal Article 2831 of the Agricultural Experiment Station, Oklahoma State University, Stillwater.

² Present address: Livestock Specialist, Agricultural Extension Service, Court House, El Centro, California 92243.

³ Present address: Professor and Head, Department of Animal Science, University of Tennessee, Knoxville 37901.

⁴ Department of Animal Science and Industry.