Ruminal in vitro batch culture evaluation of the methane mitigation potential of camelina and mustard seed co-products

The objective of this study was to evaluate in vitro ruminal fermentation of grass hay diets supplemented with increasing inclusion of camelina and mustard seed co-products. An in vitro ruminal batch culture study was conducted using a randomized complete block design with six co-products (camelina hulls, camelina meal, yellow mustard bran, yellow mustard seed, oriental mustard bran, and oriental mustard seed) included at 0, 2.5, 5, 10, and 100% DM, replacing bromegrass hay. Dry matter (DM) and fibre disappearance, cumulative gas production (GP), methane (CH4), volatile fatty acids (VFA), and ammonia nitrogen were measured. Inclusion of co-products up to 10% had no effect (P ≥ 0.06) on DM disappearance. Gas production from camelina hulls showed a quadratic response (P < 0.01), decreasing at 2.5 and 5% inclusion, without affecting CH₄ or VFA. Increasing inclusion of oriental mustard co-products up to 10% linearly reduced (P < 0.01) CH₄ production by up to 20%. When incubated alone, all co-products reduced GP and CH₄ compared with hay (P < 0.01). Overall, camelina and mustard co-products can be included at up to 10% of high forage diets without impairing nutrient disappearance, and oriental mustard products show potential for methane mitigation.