Corn Particle Passage and Size Reduction in the Rumen of Beef Steers

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Abstract
Four ruminally cannulated, 330-kg crossbred steers, fed a corn silage and 1:1 whole and cracked corn diet, were used to determine effects of particle size on ruminal corn particle passage and size reduction rates. Corn particles were sieved into classes retained on 8.0-mm (P1; approximately 83% whole corn), 4.76-cm (P2), 1.19-mm (P3) and pan (P4) screens and marked with ytterbium. Ruminal samples were taken serially after steers were successively given doses of one of the marked particle classes and cobalt ethylene diamine tetraacetic acid (Co-EDTA) through cannulas in a Latin square design. One portion of samples was homogenized and the other was wet-sieved into previously mentioned size classes. Ytterbium concentrations in whole ruminal digesta from mixed samples and the concentration of marker in whole ruminal digesta coming from each size class, as well as Co-EDTA in ruminal liquid, were determined. As particle size decreased, mean pool passage rate (P/h) increased (P<.05). The P1, P2, P3 and P4 rates averaged .019, .025, .031 and .046 for mixed and .024, .028, .022 and .046 for sieved samples. No particle reduction was detected for P1, unlike the .019 and .018 reduction rates measured for P2 and P3. Mean liquid pool passage rate (P/h) was .061. The results indicate that reducing corn particle size over the range of 8 to 1 mm will accelerate their ruminal passage rate. Intermediate-sized corn particles are reduced to smaller particles at moderate rates; however, no reduction was detected for whole corn particles placed in the rumen. Copyright © 1986. American Society of Animal Science . Copyright 1986 by American Society of Animal Science.

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