Effect of 3-nitrooxypropanol on enteric methane emissions of feedlot cattle fed with a tempered barley-based diet with canola oil

A dose-response experiment was designed to examine the effect of 3-nitrooxypropanol (3-NOP) on methane (CH4) emissions, rumen function and performance of feedlot cattle fed a tempered barley-based diet with canola oil. Twenty Angus steers of initial body weight (BW) of 356 & PLUSMN; 14.4 kg were allocated in a randomized complete block design. Initial BW was used as the blocking criterion. Cattle were housed in individual indoor pens for 112 d, including the first 21 d of adaptation followed by a 90-d finishing period when five different 3-NOP inclusion rates were compared: 0 mg/kg dry matter (DM; control), 50 mg/kg DM, 75 mg/kg DM, 100 mg/kg DM, and 125 mg/kg DM. Daily CH4 production was measured on day 7 (last day of starter diet), day 14 (last day of the first intermediate diet), and day 21 (last day of the second intermediate diet) of the adaptation period and on days 28, 49, 70, 91, and 112 of the finisher period using open circuit respiration chambers. Rumen digesta samples were collected from each steer on the day prior to chamber measurement postfeeding, and prefeeding on the day after the chamber measurement, for determination of rumen volatile fatty acids (VFA), ammonium-N, protozoa enumeration, pH, and reduction potential. Dry matter intake (DMI) was recorded daily and BW weekly. Data were analyzed in a mixed model including period, 3-NOP dose and their interaction as fixed effects, and block as a random effect. Our results demonstrated both a linear and quadratic (decreasing rate of change) effect on CH4 production (g/d) and CH4 yield (g/kg DMI) as 3-NOP dose increased (P < 0.01). The achieved mitigation for CH4 yield in our study ranged from approximately 65.5% up to 87.6% relative to control steers fed a finishing feedlot diet. Our results revealed that 3-NOP dose did not alter rumen fermentation parameters such as ammonium-N, VFA concentration nor VFA molar proportions. Although this experimental design was not focused on the effect of 3-NOP dose on feedlot performance, no negative effects of any 3-NOP dose were detected on animal production parameters. Ultimately, the knowledge on the CH4 suppression pattern of 3-NOP may facilitate sustainable pathways for the feedlot industry to lower its carbon footprint. Lay Summary Livestock methane (CH4) is the main source of greenhouse gases (GHGs) in agriculture, contributing to 11.6% of global GHGs emissions from human-related activities. Therefore, mitigating CH4 emissions from ruminant animals is a great opportunity for meeting the current climate targets. In this experiment, increasing inclusion rates of a promising CH4-mitigating compound, 3-nitrooxypropanol (3-NOP, from 50 to 125 mg of 3-NOP/kg of dry matter [DM]), were added to a barley-based feedlot diet containing 25 ppm of monensin and 7% fat (DM-basis) and fed to Angus steers. Under these conditions, increasing inclusion rate of 3-NOP reduced both production and yield of CH4 by up to 90%. Rumen fermentation, feed intake, and average daily gain were not affected by the 3-NOP dose. Our results on the potential CH4 suppression of 3-NOP may assist the feedlot industry towards sustainability by lowering its GHG output. Rumen fermentation, methane (CH4), and production parameters were investigated in feedlot cattle supplemented with increasing inclusion rates of 3-nitrooxypropanol. Our results revealed a potential CH4 abatement of up to 90% during a 90-d finishing period on a tempered barley diet containing monensin and 7% lipid content.