Effects of Forage Polyphenols on Chemistry of Ruminant Excreta and Fate of Nitrogen in the Environment.

The chemical composition of forages consumed by ruminants affects forage intake, digestion, meat and milk production, as well as manure chemistry and manure impacts on the environment. The digestion of forages by ruminants, and the decomposition of organic materials applied to soils are governed by similar chemical and microbial processes. Rumen and soil microorganisms readily digest soluble compounds (e.g., cytoplasmic proteins and non-fiber carbohydrates) followed by more recalcitrant plant fibers. Feeding polyphenolic-containing forages and tannin extracts (e.g., mixture of tannins from quebracho and chestnut trees) to sheep and dairy cattle impacts the excretion of urinary N (UN) and urinary urea N (UUN). Reduction in UN and UUN excretions due to tannin consumption by ruminants reduces environmental N loss as ammonia and nitrous oxide. The effectiveness of tannin extract in reducing ammonia emissions is due not only to reductions in UN and UUN excretions, but also due to reduced urease activity in feces. Tannins also impact the fecal N chemistry. For example, as tannin consumption by sheep and cattle increases, less endogenous N (N from microorganisms or microbial products from the rumen, small intestine, and hindgut, and N originating from the digestive tract itself) and more undigested fiber N is excreted in feces. Fecal endogenous N mineralizes much more quickly in soil than fecal fiber N.  Feces have much lower levels of polyphenolics than the forages from which the feces were derived. After incorporation in soil, feces decomposed and released N quickly whereas tannin-containing forage biomass from the source feeding trial decomposed slowly, released less N than feces, and in some cases, continued to immobilize soil N approximately one year after application to soil.