Using Tannins to Alter Nitrogen Cycling in a Grazing System.

Livestock and animal waste are significant contributors of ammonia (NH₃) and greenhouse gases (GHG). Dietary changes can impact emissions. Tannins can improve nitrogen utilization and shift nitrogen from excretion in the urine to excretion in the feces. Urine primarily consists of urea, which rapidly hydrolyzes to ammonia and volatilizes easily. In addition to the ammonia emissions, urine spots greatly exceed the N requirements of the pasture resulting in nitrogen leaching. Nitrogen in manure is in an organic form which is released more slowly, and is environmentally more friendly. Tannins may also impact GHG emissions through direct inhibitory effects on methanogens. This study examines the effect of condensed tannins (CT) on nitrogen content in urine and feces of cattle grazing forages with, and without CT. Four grasses, with and without the addition of a tannin-containing legume, are the examined in this study. The treatments include Tall Fescue (Festuca arundinacea); Meadow Brome (Bromopsis biebersteinii); Orchardgrass (Dactylis glomerata); Perennial ryegrass (Lolium perenne) planted as a monoculture; and each of the four grasses planted with Birdsfoot Trefoil (Lotus corniculatus). Treatments were grazed by Jersey heifers. Fecal grab samples and urine samples were collected at each grazing event and frozen for further analysis. Urine samples are being analyzed for ammonia, nitrate, and urea concentration. Fecal samples are being analyzed for ammonia and total N. The impact of tannins on nitrogen content in the urine and feces will be presented.