Effects of Roughage Particle Size on Site of Nutrient Digestion and Digesta Flow Through the Gastrointestinal Tract of Sheep Fed Corncob-Concentrate Diets

Abstract

An experiment examining nutritional effects of dietary corncob particle size was conducted using ruminai-, duodenal- and ileal-cannulated sheep in a 4 × 4 Latin square design. Site of nutrient digestion and digesta flow were the principal criteria evaluated. Analyses of dry matter (DM), N, starch and neutral detergent fiber (NDF) were performed on feed, feces and digesta samples. Chromic oxide-impregnated paper was used as an external marker to estimate digestibilities at different sites along the gastrointestinal tract. Ruminai pH and volatile fatty acid molar proportions were also determined. All diets (74.9% concentrates: 25.1% corncobs) were pelleted and were similar in ingredient composition but varied in corncob particle size (corncob mean particle sizes were 6.5, 5.4, 1.4 or .8 mm). Dietary crude protein levels differed little among treatments. Starch concentration was higher in diets containing the larger corncob particles while NDF, acid detergent fiber (ADF), cellulose and hemicellulose concentrations were lower in diets containing larger particles, suggesting a reaction between starch and fiber moieties during the pelleting process. Starch flow past the duodenum decreased (P<.05) as dietary corncob particle size decreased. Apparent NDF digestion before the duodenum was highest for sheep fed diets containing 1.4-mm corncobs (P<.05). Apparent starch digestion in the small intestine decreased (P<.05) as dietary corncob particle size decreased. A considerable amount of NDF was apparently digested in the small intestine of sheep consuming diets containing 5.4- and .8-mm corncobs. Likewise, a substantial amount of NDF was apparently digested in the large intestine. Few differences in apparent total tract digestibilities were noted. Sheep fed the diet containing 1.4-mm corncobs had a more rapidly increasing ruminai pH over time. The acetate:propionate ratio decreased as dietary corncob particle size decreased. Data indicate that corncob particle size influences events in the digestive tract of sheep without markedly affecting total tract digestion. Also, pelleting diets that contain concentrates and corncobs apparently results in reactions between certain nutrients in the complete diet.