271 Effects of vaccination on enteric methane emissions, growth performance, and feeding behavior of beef cattle.

Abstract Rising global temperatures have intensified the urgency to reduce greenhouse gas (GHG) emissions from anthropogenic sources, including agricultural methane (CH4). CH4 is a potent GHG produced as a byproduct of ruminal fermentation in cattle. CH4 warms the atmosphere 28 times more than carbon dioxide (CO₂) over a 100-year period, making it a critical GHG mitigation target. Multiple approaches are being developed, but the beef cattle industry lacks solutions that effectively reach ~80% of bovine CH4 emissions produced in extensive, pasture-based systems, e.g., the cow-calf and stocker segments. One promising approach is a methane-reducing vaccine. Methane-reducing vaccines stimulate the production of anti-methanogen antibodies. These antibodies potentially enter the rumen, bind to their methanogen targets, and inhibit ruminal methanogenesis, thereby reducing enteric CH4 emissions. The objective of this trial was to assess the effect of a proto-type vaccine on growth performances, gas flux, and feeding behavior in beef cattle. Thirty Angus crossbred steers (n = 30; 451 ± 11 kg) were blocked by body weight (BW) and stratified by breed before being randomly assigned to one of two treatments: control (n = 20) or vaccine-treated (n = 10). Animals received a prime-boost vaccine regimen (2 mL, each) administered subcutaneously on days 0 and 21. Animals were housed in three pens, each equipped with three electronic feed bunks (Vytelle, Lenexa, KS) for recording individual feed intake and feeding behavior, as well as one GreenFeed emission monitoring system (C-lock Inc., Rapid City, SD) for measuring CH4 emissions. Weekly BW, daily feed intake, and gas emissions were measured over an 84-day period. Statistical analyses were conducted in JMP Pro v.16 (SAS Institute Inc., Cary, NC), with individual animals as the experimental unit, and treatment as a fixed effect. There were no significant differences in average daily gain (ADG), initial BW, mid-test metabolic BW (BW⁰·⁷⁵), DMI, alfalfa pellet intake or gain: feed (P > 0.05). The vaccine-treated group had 15% lower (P = 0.0050) CH4 production (g/d), 18% lower (P = 0.0038), CH4 intensity (g/kg BW 0.75) and 13% lower (P = 0.0149) CH4 yield emissions (g/kg DMI) compared to the control. However, CO2 production (g/d), CO2 yield (g/kg DMI) and H2 production (g/d) did not differ (P > 0.05). Bunk visit (BV) duration was also similar between groups (P > 0.05). However, the vaccine-treated group had fewer BV per day (P = 0.0292) and a longer BV head-down duration per day (P = 0.0105), with a tendency for a slower eating rate (P = 0.0697) compared to control. These results highlight the potential of vaccination as a strategy to mitigate enteric CH4 production in beef cattle without negatively impacting growth performance.