Effects of partially replacing grass silage by lucerne silage cultivars in a high-forage diet on ruminal fermentation, methane production, and fatty acid composition in the rumen and milk of dairy cows

Abstract

Lucerne silages of the Kometa and Verko cultivars were investigated in four consecutive experiments to evaluate their effects on ruminal fermentation and fatty acid (FA) proportions in the rumen fluid and milk of dairy cows. Initially, two successive in vitro experiments were performed using a semicontinuous culture system (RUSITEC). In Experiment 1, the treatments were: (1) MGS: a high-forage diet (65:35 forage:concentrate ratio; DM basis) containing maize silages (MS) and grass silages (GS) as the main forage sources, (2) MKLS: a high-forage diet containing MS and Kometa lucerne silage (KLS) as the main forage sources; and (3) sMKLS: a high-forage diet containing MS and KLS as the main forage sources and supplemented with sufficient saponin extract powder from KLS to give a saponin content equal to the in the KLS. The treatments in Experiment 2 (MGS, MVLS, or sMVLS) were similar to those in Experiment 1, except that Verko Lucerne silage (VLS) and its saponin extract were used. Methane concentration statistically insignificant decreased (P = 0.97) as a result of the MKLS treatment, while digestible dry matter (DDM) was increased (P = 0.002) for MKLS and sMKLS. However, neither methane concentration nor DDM were affected by MVLS or sMVLS. We also performed two in vivo experiments: in Experiment 3, we used six cannulated Polish Holstein-Friesian cows fitted with rumen cannulas, and in Experiment 4, we used 54 productive Polish Holstein-Friesian cows. The treatments for these two experiments were based on partial replacement of GS with KLS or VLS in the high-forage diet containing MS, as described earlier: MGS, MKLS, and MVLS. In Experiment 3, the methane concentration decreased (P < 0.001) for both MKLS and MVLS, with the diets lowering the total bacterial and protozoal counts and the total methanogens (P ≤ 0.002). Interestingly in Experiment 4, only MVLS led to a decrease in fat content and energy (P ≤ 0.02). MKLS and MVLS were also associated with lower levels of milk polyunsaturated fatty acid (P < 0.001) and higher levels of milk saturated fatty acid (P < 0.001). MKLS had more promising fatty acid composition than MVLS, with clearer methane mitigation. In conclusion, the Kometa lucerne silages inhibited methane emission and microbial population, but at the cost of increasing the saturated fatty acids in the milk fat.