Exploring a long transition period for bromoform-based feed additive supplementation with rumen modifiers in ewes

Context Bromoform (CHBr3)-based feed additives are effective at mitigating enteric methane (CH4) emissions from ruminants but may induce a reduction in dry-matter intake (DMI), especially when introduced rapidly at high inclusion levels. Co-supplementation of CHBr3 with rumen modifiers such as Ascophyllum nodosum (ASCO), grape marc (GM), or biochar may mitigate this adverse effect, although evidence under high-forage diets remains limited. Aims This study investigated whether a long transition strategy could improve animal responses to CHBr3 supplementation and whether co-supplementation with rumen modifiers affects intake and rumen fermentation in ewes maintained on a high-forage diet. Methods Twenty-eight Merino ewes were assigned to six treatments: control (T1), CHBr3 only (T2), CHBr3 + ASCO (T3), CHBr3 + GM (T4), CHBr3 + biochar (T5), or CHBr3 + ASCO + GM + biochar (T6). Animals were gradually transitioned to CHBr3 over 31 days at low inclusion rates (8.3–16.6 mg/head.day), followed by a 16-day period at higher inclusion rates (24.9–33.12 mg/head.day). Measurements included DMI, liveweight, average daily weight gain (ADWG), gain-to-feed ratio (G:F), rumen pH, and volatile fatty acid (VFA) concentrations. Results At the higher CHBr3 inclusion levels, DMI decreased relative to the control (T1) by 5% in T2 and T5, 9% in T4, 16% in T3, and 14% in T6. Despite these reductions in intake, animals in T2 and T5 gained weight across periods. The ADWG and G:F remained similar among treatments. Supplementation with CHBr3 alone increased total VFA concentrations by 112% and shifted rumen fermentation towards higher proportions of propionate and butyrate and lower acetate. However, co-supplemented treatments showed lower total VFA concentrations and variable shifts in individual VFA profiles, suggesting that each rumen modifier interacted differently with CHBr3. Conclusions A 31-day transition strategy effectively reduced the typical DMI suppression associated with high CHBr3 inclusion, particularly when CHBr3 was fed alone. In addition, CHBr3-only supplementation produced the most favourable rumen fermentation profile. Implications A long transition strategy could enhance the practical application of CHBr3-based CH4 mitigation technologies in high-forage production systems by stabilising intake while promoting beneficial rumen fermentation.