Effects of intake and forage level on site and extent of digestion of plant cell wall monomeric components by sheep.

The objective of this experiment was to study the effects of level of intake and proportion of forage in the diet on site and extent of digestion of plant cell wall monomeric components (phenolics, neutral sugars) by sheep. Four Suffolk wethers (65 kg) with ruminal and duodenal cannulas were fed diets containing 75% (75A) or 25% (25A) alfalfa hay at two levels of intake, 1,700 (high intake, HI) or 1,100 (low intake, LI) g DM/d in a 4 X 4 latin-square design with a 2 X 2 factorial arrangement of treatments. The remainder of the diet consisted primarily of ground corn. Wethers had lower (P less than .05) total tract NDF and ADF digestibilities when fed 75A or at HI. An intake X forage level interaction (P less than .05) was noted for non-core lignin ferulic acid (FA) total tract disappearance, with wethers at LI having the highest, 25A-HI having the lowest, and 75A-HI having an intermediate FA disappearance. Wethers fed at LI had higher (P less than .05) total tract disappearance of non-core lignin p-coumaric acid (PCA). Wethers fed 75A had greater (P less than .05) total tract disappearances of core lignin vanillic acid (VA) and vanillin (VAN). Total tract digestibilities of the neutral monosaccharides glucose (GLC), xylose (XYL), arabinose (ARA) and galactose (GAL) were greater (P less than .05) for LI vs HI treatments. Wethers consuming 75A had greater (P less than .05) total tract ARA and GAL digestibilities, whereas wethers fed 25A had greater (P less than .05) total tract digestibilities of GLC and mannose (MAN). Diet composition and level of intake appear to influence site and extent of digestion of cell wall monomeric components.