336. Evaluation of Granular and Oil Formulations Containing Synthetic Bromoform for Methane Mitigation in Beef Cattle.

Abstract Bromoform is a halogenated compound with strong potential to mitigate enteric methane (CH4) emissions through targeted inhibition of ruminal methanogenesis. It is naturally found in red macroalgae (Asparagopsis spp.); however, its high reactivity and volatility require stabilization. Synthetic bromoform provides a scalable and consistent alternative to seaweed-derived sources, reducing variability and logistical constraints. This study evaluated the effects of synthetic bromoform stabilized in oil and a granular Investigational Veterinary Product (IVP) on CH4 emissions in beef cattle. Sixty-four Angus-crossbred steers (352 ± 44 kg BW) were used in a completely randomized design over 62 d and assigned to one of four treatments (n = 16): control (CON), oil IVP (OIL), granular IVP at 5% bromoform (GR5) or granular IVP at 10% bromoform (GR10). All bromoform treatments were provided at a target dose of 30 mg/kg DM via a DDGS-based premix (1% of diet DM). The study included 24 d of diet and treatment adaptation and 38 d of data collection. Data were analyzed using the MIXED procedure of SAS, and orthogonal contrasts were performed to evaluate the effect of bromoform (B vs. CTL), the effect of bromoform formulation (OIL vs. GR), and the effect of bromoform concentration within the granular carrier (5 vs. 10). Total VFA concentration (mM) was not affected by bromoform treatments (B vs. CTL; P = 0.17), formulation (GR vs. OIL; P = 0.69), or concentration within the granular carrier (5 vs. 10; P = 0.84). However, bromoform decreased the molar proportion (MP; mol/100 mol) of acetate (B vs. CTL; P < 0.01) and increased the MP of propionate (B vs. CTL; P = 0.002). Consequently, the acetate to propionate ratio was greater in CON than in bromoform-treated groups (B vs. CTL; P < 0.01). Dry matter intake was reduced by bromoform treatments by an average of 1 kg DM/d (B vs. CTL; P < 0.01), with no differences between formulation (GR vs. OIL; P = 0.09) or concentration (5 vs. 10; P = 0.78). Final body weight was not affected by bromoform (B vs. CTL; P = 0.08) and did not differ between formulation (GR vs. OIL; P = 0.143) or concentration (5 vs. 10; P = 0.51). Similarly, gain-to-feed ratio was also unaffected by treatment (P > 0.05). Bromoform treatments decreased enteric CH4 emissions by 84% (B vs. CTL; P < 0.01), with no differences between formulation (OIL vs. GR; P = 0.671) or concentration (5 vs. 10; P = 0.465). These results indicate that both oil and granular formulations of bromoform are equally effective at reducing enteric methane emissions and shifting ruminal fermentation profile when administered at equivalent doses, with no additional benefit of increasing bromoform concentration within the granular IVP.