Irrigated birdsfoot trefoil (BFT; Lotus corniculatus L.) is a productive, persistent perennial legume in the Mountain West region of the United States of America (USA) (MacAdam and Griggs 2006). It does not cause bloat, even when grazed in pure stands, because it contains a relatively small amount (2-4% of dry matter (DM)) of condensed tannins (Mueller-Harvey 2006; Waghorn 2008). Birdsfoot trefoil tannins bind excess plant proteins at rumen pH (~ pH 6.2) sufficiently to prevent bloat and then release these proteins into the abomasum at gastric pH (~ pH 2.5). This allows plant proteins to be digested to amino acids that can be absorbed in the small intestines (Waghorn et al. 1987). Short-term increases in productivity have been demonstrated in beef cattle (Wen et al. 2002) and dairy cows (Woodward et al. 1999) grazing BFT, but few studies have looked at longer-term effects on commercial farms.