Corn Particle Size and Site and Extent of Digestion by Steers

Abstract

The site and extent of starch digestion by steers as influenced by corn particle size was studied in a 4 x 4 Latin square design. Steers (272 kg) fitted with permanent rumen cannulae were fed approximately 3.5 kg dry matter in eight portions daily (3-hr intervals). Site of digestion was estimated by withdrawing rumen samples and assuming such samples would be equivalent to abomasal samples if a constant flow of digesta was maintained by frequent feeding. Ruminal digestion of dry matter (DMD), organic matter (OMD) and starch was estimated by the ratio of permanganate lignin in feed to lignin in rumen digesta. Corn was fed whole or following grinding through 3.18, 4.76 or 7.94mm screens and comprised 72% of the diets. Geometric mean diameters (micrometers) of the four grains were as follows: whole (5978 /am), 3.18mm (509/am), 4.76mm (588/am) and 7.94mm (832/am). In view of high and variable lignin digestibil-ities, ruminal digestibility estimates indicate trends rather than absolute values. Ruminal DMD was lower (P