36. Investigating the Dose-Response Pattern of a Blended Condensed and Hydrolyzable Tannin Extract on Diet Digestibility and Methane Production in Beef Cattle.

Abstract Feed additives have gained attention for their potential to optimize rumen fermentation and mitigate methane (CH4) production. Among these, condensed tannins (CT) have demonstrated the ability to reduce CH4 production. However, the synergistic efficacy of supplementing a combined condensed and hydrolyzable tannin (HT) extract has received limited evaluation. The objective of this study was to investigate the dose-response of a blended tannin extract (TE) in a total mixed ration (TMR) on intake and excretion, diet digestibility and ruminal parameters, nitrogen (N) metabolism, and gas exchange. Utilizing eight British crossbred steers (215±18 kg) in a 4 × 8 Latin rectangle design, TE was included in the diet at 0, 0.15, 0.3, and 0.45% (TE0, TE0.15, TE0.3, TE0.45) of dietary dry matter (DM), with the TMR fed at 1.8% of BW (DM basis). During the four-period trial, each animal received each treatment once, with each treatment being assigned in duplicates per period. For 48 h, whole-animal gas exchange, as well as total fecal and urine excretion, and intake were measured using two open-circuit, indirect calorimetry respiration chambers. Blood and rumen fluid samples were collected from steers immediately after removal from the chambers to evaluate blood urea nitrogen (BUN) and ruminal parameters (e.g. pH, Redox, volatile fatty acid concentrations). The inclusion rate of TE had no influence on nutrient (P ≥ 0.23) and water intake (P ≥ 0.57). However, fecal DM (P = 0.05) and fecal excretion of acid detergent fiber (ADF; P = 0.02) increased linearly, with a tendency for fecal excretion of neutral detergent fiber (NDF; P = 0.08) to increase linearly. Digestibility of ADF (ADFD) displayed a linear decrease with increasing inclusion of TE (P = 0.05), with no other influences on diet digestibility (P ≥ 0.20). There was no influence of TE rate on ruminal parameters (P ≥ 0.19). Digestibility of N tended to decrease (linear, P = 0.07; quadratic, P = 0.09) while fecal N excretion linearly increased (P = 0.02) with higher inclusion of TE. However, there was no effect of TE rate on retained N (P ≥ 0.13) or urinary N excretion (P ≥ 0.20). In addition, TE dose had no influence on gas exchange, including consumption of oxygen and emissions of carbon dioxide and CH4 (P ≥ 0.40). In summary, the TE supplementation altered N utilization and fiber digestion, as evidenced by increased fecal N excretion and reduced ADF digestibility; however, it did not improve N retention or reduce CH4 emissions. These results suggest that, under the conditions of this study, blended TE influenced nutrient utilization more than CH4 mitigation. Therefore, additional research is needed to gain further insight into the possible synergistic effects of a blended TE when supplemented to beef cattle diets.