Tannin Supplementation Alters Foraging Behavior and Spatial Distribution in Beef Cattle

We investigated how tannin supplementation influences the behavior and performance of beef cattle grazing a meadow bromegrass monoculture. Twenty-four Angus cow–calf pairs were allocated to six 3.6-ha paddocks (four pairs/paddock), randomly assigned to Control (Ctrl; n = 3) or Tannin treatment (TT; n = 3). Animals received 1 kg/cow/day of DDGs, with TT receiving an added 0.4% tannins (2:1 condensed:hydrolyzable). Grazing occurred during four 15-day periods (July–September) across two years. Data were analyzed with mixed-effects models. Tannins did not alter biomass removal or cow weight loss (p > 0.05). However, TT cows exhibited longer evening grazing (2.9 vs. 2.1 h), fewer standing-to-lying transitions (5.7% vs. 7.3%), and more even grazing distribution (CV = 1.86 vs. 2.13; p < 0.05), and greater water consumption (147 vs. 121 L/day; p < 0.01). Average daily gain of calves was numerically greater in TT compared to Ctrl (1.03 vs. 0.93 kg/day), although this difference was not significant (p = 0.2699). Findings indicate that tannin supplementation extended evening grazing, reduced rumination, and promoted even distribution, indicative of increased forage selectivity. Fewer standing-to-lying transitions indicated reduced restlessness, potentially improving welfare. Increased water intake highlights a physiological adjustment that may require management in water-limited rangelands.