Roughage Content and Particle Size: Their Effects on Size Reduction and Fiber Composition of Particles Passing Through the Gastrointestinal Tract of Sheep fed Corncob-Concentrate Diets

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Abstract
Pelleted diets varying in content of corncobs (45.1, 35.1, 25.1 or 15.1% of the diet) or in fineness of grind of the corncob fraction (6.5, 5.4, 1.4 or 0.8 mm mean particle size) were fed to ruminal-, duodenal- and ileal-cannulated sheep to evaluate changes of digesta mean particle size and fiber composition with passage of diets through the gastrointestinal tract. As diets decreased in quantity of corncobs (experiment 1) or in mean particle size of the corncob fraction (experiment 2), mean particle size of diet also decreased. Percentage dietary corncobs influenced fecal mean particle size (higher percentage corncobs in diets resulted in larger fecal mean particle sizes). Fecal mean particle size was not affected by mean particle size of the corncob fraction of the diet (experiment 2). In both experiments, fiber concentration decreased as feed, digesta and fecal particles decreased in size. The only exception was acid detergent lignin content of digesta and fecal particles where concentration decreased and then increased as particle size decreased. Fiber concentration of separated particles tended to increase as digesta moved through the gastrointestinal tract. Reduction of particle size was greater when dietary corncob amount was high. Particle size of the dietary corncob fraction altered fiber composition of particles and reduction of particle size of the diet with passage through the gastrointestinal tract of sheep.