PSXIII-14 Evaluation of two levels of 3-nitrooxypropanol (3-NOP) as feed additive on methane emission, rumen microbiome, animal performance, dry matter intake and digestibility, of Nellore cattle in a feedlot.

Abstract The efficacy of 3-NOP in reducing enteric methane (CH4) emissions in dairy and beef cattle diets is well-documented. However, to our knowledge, there are no studies evaluating inclusions of 3-NOP in dosages lower than 100 ppm under tropical conditions in Nellore animals. Therefore, this study aimed to evaluate two levels of 3-nitrooxypropanol (3-NOP) as a feed additive on performance, CH4 emission, and rumen microbiome of Nellore cattle in a feedlot. Seventy-five 20-month-old Nellore bulls [361.6 ± 30.08; body weight (BW) ± SD] were individually housed with ad libitum access to feed and water. Animals were distributed in a completely randomized design, with 3 treatments, 25 animals per treatment. The treatments were: 1) CON, control (basal diet + mineral premix with monensin 25 mg/kg DM without additive 3-NOP), 2) 3-NOP65 (Basal diet + mineral premix with monensin 25 mg /kg DM + 65mg/kg of DM of 3-NOP; Bovaer®), 3) 3-NOP85 (Basal diet + mineral premix with monensin 25 mg /kg DM + 85 mg/kg of DM of 3-NOP; Bovaer®). The adaptation dietary program consisted of ad libitum feeding of 3 adaptation diets for 3 weeks (21 days), with the concentrate level of the diet increasing from 50 to 60% in week 1, 60 to 75% in week 2, and 75 to 88% in week 3, DM basis. The experiment lasted 115 d. Enteric CH4 emissions were estimated using the sulfur hexafluoride (SF6) tracer gas technique (16 animals per treatment), during the 104 to 110 days of the experimental period. Rumen microbiome samples, from the same 16 animals used for CH4 data, were collected on d 115 at the slaughterhouse, samples were processed and analyzed with the ZymoBIOMICS® Targeted Sequencing Service. The animal performance was not affected by the increasing doses of dietary 3-NOP. Dry matter intake increased linearly in response to 3-NOP addition. The 3-NOP inclusion tended to quadratically increase the digestibility of DM (P = 0.07), and quadratically increase the digestibility of CP (P = 0.04). The addition of 65 and 85 mg/kg of 3-NOP (DM basis) was effective on reducing CH4 emissions by 13.2 and 26.7%, respectively, when compared to CON diet with no detrimental effects on animals’ health. Likewise, linear reduction was detected for CH4 the emission intensity of CH4 per HCW by 14.3% and 27.6% at doses 65 and 85 mg/kg of DM. There was a reduction of the relative abundance of the phyla Euryarchaeota with increasing doses of 3-NOP, a phylum that encompasses methanogen microorganisms. Overall, increasing doses of 3-NOP were effective in reducing CH4 emissions of Nellore cattle in a feedlot system in a dose-dependent manner, with no detrimental effects on animals’ performance and health.