Methane mitigation in practically applicable dairy diets: Impact of diet composition and extruded linseed

Recognized strategies to mitigate methane (CH4) emissions from dairy cows include increased levels of dietary starch or lipids. Most studies have tested extreme experimental diets that are rarely applied in practice, as farmers generally apply lower concentrations. In the present study we evaluated the effects of partial replacement of grass silage (GS) with corn silage (CS) and extruded linseed (EL) supplementation in optimized dairy cattle diets under conventional farming conditions. Three 15-week experiments were conducted in three periods: adaptation (3 weeks), pre-treatment (6 weeks), and treatment (6 weeks). A reference group receiving a control diet was compared to each treatment group. In EXP1, GS (65 % GS, 35 % CS) was partially replaced with CS (35 % GS, 65 % CS). In EXP2 and EXP3, EL (13.8 % of dietary DM, fat increased by 1.5 %) was added to a CS-based (EXP2) and to a GS-based diet (EXP3). No significant effect was observed on milk production and CH4 emissions when replacing GS with CS. EL addition to the CS-based diet showed a trend toward a 9 % reduction in CH4 production and yield (p = 0.097 and p = 0.074), while no significant effect of EL was observed for the GS-based diet. In summary, replacing GS with CS had no effect on production or CH4 emissions, while adding EL to a CS-based diet showed potential for CH4 mitigation. This study shows that recognized CH4 mitigation strategies may not prove effective when diets are optimized based on practical guidelines for high-producing dairy cows.