Phenolic compounds in roughages and their fate in the digestive system of sheep.

Three experiments were conducted to determine the concentrations of phenolic monomers (para-coumaric acid, ferulic acid, vanillin, acetovanillone, para-hydroxybenzaldehyde and para-hydroxyacetophenone) and polymers (lignin) in roughages and to assess the fate of these compounds in the ruminant digestive system. In Exp. 1, low quality t imothy hay and cottonwood, silver maple and red oak sawdusts were fed to mature wethers. Apparent digestibilities of dietary dry matter, hemicellulose and starch were similar among treatments. Cellulose digestibility of t imothy hay was greater than that of the wood cellulose diets. Digestibility of klason acid detergent lignin (ADL) of t imothy hay and the maple sawdust diet was greater than that of the cottonwood and oak diets. Lower concentrations of phenolic monomers were present in fecal lignins than in feed lignins when animals were fed any of the three sources of sawdust. In Exp. 2, cot tonwood sawdust was fed fresh or after drying, ensiling or treatment with propionic acid. No differences in dry matter digestibility or hemicellulose digestibility were observed among treatments, but cellulose digestibility of fresh sawdust was greater than that of the treated roughages. Lignin of dry sawdust was more poorly utilized than was the lignin of the treated materials. As in Exp. 1, smaller amounts of phenolic monomers were present in feces than in feed. In Exp. 3, growing lambs were fed alfalfa or bromegrass hay to enable us to monitor selectively the disappearance of phenolic material from various sections of the