Evaluating dose–response patterns of a tannin extract blend on nutrient utilization and methane emissions in beef cattle

Tannin extracts (TE) of isolated condensed or hydrolyzable tannins have been evaluated for their methane (CH4) mitigation potential in beef cattle. Despite the potential for a combination of tannin types to yield synergistic effects, the dose-response pattern and optimal supplementation rate of a TE blend remain unclear. Our objectives were to investigate changes in nutrient utilization and gas emission patterns in response to supplementation with a TE blend (Silvafeed ByPro; SILVATEAM, San Michele Mondovi, Italy), and to determine the optimal dose to minimize emissions in growing steers (308 ± 9.4 kg BW). Supplementation rates were 0.0%, 0.3%, 0.6%, and 0.9% of DM (TE0.0, TE0.3, TE0.6, and TE0.9, respectively) within a total mixed ration fed at 1.62% of BW (DM basis). Whole-animal gas exchange and total fecal and urine production were measured over 48 h using two open-circuit, indirect calorimetry respiration chambers in a 4 × 8 Latin rectangle design with four periods and eight animals. Blood and ruminal parameters were evaluated from samples collected from steers upon removal from chambers. Nutrient and water intake were not influenced (P ≥ 0.42) by TE rate. Fecal excretion of acid detergent fiber (ADF) displayed a dose-response pattern (quadratic P < 0.01, cubic P = 0.01) with increasing TE rate. Apparent digestibility of ADF decreased at an increasing rate (quadratic P < 0.01, cubic P = 0.01) with TE. There was a quadratic effect (P = 0.01) on ruminal propionate concentration, but no other ruminal parameters were influenced by TE rate (P ≥ 0.13). There was a quadratic pattern (P = 0.04) in fecal N excretion and N digestibility. The rate of TE did not affect urinary N excretion (P ≥ 0.58), but N retention tended to linearly decrease (P = 0.06) with increased TE and blood urea N tended (P = 0.06) to follow a cubic pattern. There was a quadratic (P ≤ 0.05) dose-response relationship for gaseous energy loss. Although oxygen consumption and carbon dioxide production were not influenced by TE rate (P ≥ 0.64), the respiratory quotient increased linearly (P = 0.02) with TE inclusion. However, no other energy partitioning was influenced by TE supplementation rate (P ≥ 0.18). Regardless of how it was expressed, CH4 production displayed a quadratic pattern (P ≤ 0.04) in relation to increased TE rate, with equations suggesting an optimal TE dose between 0.20 and 0.22% of DM for CH4 mitigation without compromising nutrient utilization or energy efficiency.