174 Effects of tannin extract supplementation rate on beef cattle energy expenditure and nitrogen balance.

Abstract Tannin extracts (TE) are primarily composed of two tannin types: condensed tannins (CT) and hydrolyzable tannins (HT). Several studies have evaluated the effects of supplementing beef cattle with either CT or HT, particularly on methane mitigation and metabolic functions. However, supplementing a combination of both tannin types may yield synergistic effects. Despite this potential, the optimal supplementation rate for the combined use of CT and HT has yet to be determined. Thus, our objective was to investigate the impact of a blended CT and HT extract (Silvafeed ByPro; SILVATEAM, San Michele Mondovi, Italy) supplemented at 0.0, 0.3, 0.6, and 0.9% of DM (TE0.0, TE0.3, TE0.6, and TE0.9, respectively) within a roughage-based total mixed ration on energy partitioning and nitrogen balance of growing British crossbred steers (372 ± 39 kg BW). A 4 × 8 Latin rectangle design consisting of four experimental periods and eight animals was used to measure whole-animal gas exchange and total collection of feces and urine over a 48-h collection period using two open-circuit, indirect calorimetry respiration chambers. Animals were fed the basal diet at 1.62% of BW on a dry matter (DM) basis. DM and gross energy intakes were not impacted by TE inclusion rate (P ≥ 0.51), averaging 5.87 kg/d and 25.36 Mcal/d, respectively. The TE inclusion rate affected methane (CH4) energy loss (P = 0.03), in which TE0.3 had the least and TE0.9 had the greatest CH4 energy loss, with TE0.0 and TE0.6 being intermediate. There were no differences in digestible energy, metabolizable energy, heat energy, or retained energy among TE supplementation rates. Daily fecal nitrogen excretion tended to increase (P = 0.09) and apparent digestibility of nitrogen tended to decrease (P = 0.08) with increased inclusion of TE, but there were no differences in urinary nitrogen excretion or retained nitrogen (P ≥ 0.29). Our results indicate that the commercial blend of CT and HT extract does not impact energy or nitrogen retention when supplemented at a rate of up to 0.9% of DM intake. The TE0.3 supplementation rate may have the most significant potential to reduce CH4 energy loss. However, the ideal level and the mechanism of action for the effect of TE on CH4 production requires further investigation.