PSV-10 - Vaccination of beef cattle to reduce enteric methane emissions

Abstract: Livestock methane (CH4) emissions total over 3 billion tonnes per year of carbon dioxide equivalents (CO2e) and are responsible for approximately 6% of total annual greenhouse gas emissions. The contribution of livestock CH4 emissions are only to be exacerbated as the global demand for meat and dairy products increases. Greater than 75% of livestock CH4 emissions are generated in dispersed production environments (e.g., cow-calf and stocker segments), which are not addressable by methane mitigation strategies requiring constant inputs. Thus, strategies that fit into standard agronomic practices, in particular dispersed production environments, are urgently needed to address the increasing carbon footprint associated with livestock production. Methane-reducing vaccines are a promising solution for addressing this need, due to their longevity of action, low cost, and ease of integration into standard agronomic practices, which could lower the barrier for adoption. Thus, this study aimed to assess the effects of a prototype vaccine on total and antigen-specific immune response, CH4 yield, and average daily gain (ADG) in cattle. Twenty Angus crossbred steers (initial BW 537±15 kg) fed on a high-forage diet were randomly assigned to either placebo- or vaccine-treated groups blocked by body weight, breed, and feed intake. Steers were subcutaneously inoculated (2 mL dose) in the anterior region of the neck. Blood and saliva samples were collected, and total sera and salivary IgG and IgA were quantified using ELISA (Bethyl laboratories, Montgomery, TX). Antigen-specific sera IgG was measured using ELISA. Daily CH4 emissions and dry matter intake (DMI) were measured using GreenFeed systems (C-Lock Inc. Rapid City, SD) and GrowSafe feed bunks (Vytelle, Lenexa, KS), respectively. Body weights were recorded bi-weekly. Total sera IgA and IgG did not differ between the placebo-treated and vaccinated steers (P=0.584, P=0.425, respectively), nor did total salivary IgA and IgG (P = 0.577 and P =0.548, respectively). However, antigen-specific sera IgG did significantly increase following booster vaccination in the vaccinated steers, as compared to placebo-treated steers (d0 vs. d28; P < 0.001). CH4 yield was significantly reduced in vaccinated steers following booster vaccination despite significantly increasing in placebo-treated steers over the same period (P=0.002). This reduction in CH4 yield was not associated with a reduction in DMI nor ADG (P=0.181 and P</em>=0.314, respectively), suggesting that vaccination did not negatively affect treated animals. These findings underscore the potential of vaccine-based solutions to mitigate the environmental impact of livestock CH4 emissions, especially from dispersed production environments where current options for mitigation strategies are limited.