Fermentation characteristics and methane production of rations with high-lipid feed alternatives in vitro

This study evaluated the effects of barley and four oat cultivars differing in lipid content, including one high-oil cultivar, and the replacement of rapeseed meal (RSM) with cold-pressed rapeseed cake (RSC), on in vitro ruminal fermentation, degradability, and methane (CH4) production. An in vitro gas production experiment was conducted using a 5 × 3 factorial arrangement of treatments with four 48-h runs. Treatments included a barley mixture [22.6 g crude fat/kg dry matter (DM)] and the oat cultivars Sonja, Niklas, Perttu, and the high-oil oat cultivar Fatima (41.2, 53.7, 58.5, and 81.2 g crude fat/kg DM, respectively), each combined with three levels of RSC (0, 50, and 100 % of protein feed). The basal diet consisted of grass silage (550 g/kg diet DM). Dynamic rumen models were applied to in vitro gas data to predict in vivo CH4 production. Predicted CH4 production (mL/g DM) was 8.3, 9.0, and 12.6 % lower, respectively, for Niklas, Perttu, and Fatima compared with barley (P ≤ 0.01), and was also lower for Fatima than for Sonja and Niklas (P ≤ 0.01). Replacing RSM with RSC linearly reduced predicted CH4 production by 4.3 % (P ≤ 0.01). In vitro ruminal DM and organic matter degradability were lower for all oat cultivars compared with barley (P ≤ 0.01), and further reduced for Perttu and Fatima compared with Sonja (P ≤ 0.04). Acetate proportion was higher for Sonja, Niklas, and Perttu than for barley and Fatima (P ≤ 0.02), while propionate was higher for Perttu and Fatima than for barley, at the expense of butyrate (P ≤ 0.02). In conclusion, high-oil oats and RSC each reduced predicted in vivo CH4, with additive effects when combined. However, high-oil oats also lowered in vitro ruminal degradability. Further in vivo studies are required to evaluate effects on digestibility, CH4 production, and animal performance.