Evaluation of increasing levels of condensed tannin extracted from Acacia mearnsii on performance, carcass traits, meat quality, methane emission, and health of finishing Nellore bulls

The objective of this study was to evaluate the impact of increasing levels of condensed tannin extracted from Acacia mearnsii on the performance, carcass traits, meat quality, methane (CH₄) emissions, and health of finishing Nellore bulls in a feedlot system. Eighty 20-month-old Nellore bulls (426.7 ± 24.46 kg of body weight (BW)) were individually housed with ad libitum access to feed and water. The study followed a completely randomized design with five treatments, each consisting of sixteen animals. Treatments included a negative control (no additives), 3 levels of tannin (0.8, 1.6, and 3.2 g of tannin/kg DM; Tanfeed®, Tanac Company), and a positive control (28 mg/kg DM monensin; Elanco®). Animals underwent a 21-day adaptation period with three step-up adaptation diets before entering the 89-day finishing phase. The adaptation dietary program consisted of ad libitum feeding with 3 adaptation diets over 21 days, in which the finishing phase lasted 89 days. The adaptation dietary program consisted of ad libitum feeding of 3 step-up adaptation diets for 3 weeks (21 d). The concentrate level of the diet (DM basis) increased from 40 % to 50 % in week 1, 50–56 % in week 2, and 56–75 % in week 3 (finishing diet). The experimental period (adaptation + finishing phases) lasted 110 d. The diet was formulated to meet the requirements while considering an average daily gain (ADG) of 1.6 kg/d. Enteric CH₄ emissions were estimated using the sulfur hexafluoride (SF₆) tracer gas technique. Performance and carcass traits, except for shear force and ash in meat, were not affected by increasing levels of dietary tannin or monensin (P>0.10). Regression analysis indicated a quadratic effect on shear force, with the lowest value observed at 1.6 g/kg DM of dietary tannin inclusion (P=0.05). Ash in meat increased quadratically with tannin inclusion, peaking at 1.6 g/kg DM of tannin addition, differing from monensin-treated bulls (P=0.05). However, CH₄ emission as g/d decreased quadratically with increasing tannin levels (P<0.01), reaching the lowest emission at 0.8 g/kg DM of tannin inclusion, differing from monensin treatment (P<0.01). Also, CH₄ emission intensity (g/kg DMI at CH₄ sampling period) tended to decrease quadratically with tannin inclusion (P=0.09), with the lowest intensity observed at 0.8 g/kg DM of tannin inclusion, but not differing from monensin-treated bulls. Liver abscess and rumen scores were not impacted by tannin level in the diet (P = 0.26 and 0.19, respectively); however, the odds of having a liver (0 to A+ scale) and ruminitis score (0-10 scale) of 0 was 0.178 less for monensin-treated bulls compared to control and 0.224 less for monensin than tannin-treated bulls at 3.2 g/kg DM of inclusion, respectively. Overall, condensed tannin effectively reduced meat shear force and CH₄ emissionin finishing Nellore bulls in a dose-dependent manner, without detrimental effects on performance.