CONCLUSIONS
The use of soybean hulls (15% of DM) in partial replacement of corn meal increased dietary fiber concentration without affecting DMI, and milk production, and CH4 yield (g/kg of DMI). The high-starch diets tended to reduce CH4 intensity (expressed as g/kg of milk). Fish oil at the dosage tested (0.8% of DMI) tended to enhance milk yield and positively decreased the n-6:n-3 ratio of the milk PUFA, but did not reduce methane emission. However, in low-starch diets, the addition of FO seems promising in reducing CH4 intensity per kilogram of ECM. The use of FO as dietary lipid supplement is not advisable for high-starch diets due to the negative effect on milk fat. The surprising increase in NDF digestibility due to FO in corn silage-based diets deserves further study to determine the dynamics of the rumen microbial populations. Interestingly, the increase in NDF digestibility due to FO did not increase CH4 yield.