Enteric Methane Emission and Nitrogen Excretion of Lactating Cows Fed Soybean-Hulls as Partial Replacement of Corn Grain

Including soybean hulls (SH) in ruminant diets increase the carbon circularity of livestock systems. We evaluated whether SH could partially replace corn grain (CG) in the diet of lactating cows (≈7.5% of the total diet). Six Holstein multiparous cows were fed a 50:50 (dry matter basis) corn-silage to concentrate diet for two 25-day periods in three replicated 2 × 2 Latin Squares using linear mixed models. Feed intake, milk yield and composition, N excretion, CH₄ production, and ruminal microbial profiles were measured. Enteric CH₄ was measured in respiration chambers. The DMI of cows fed SH (28 kg DM/d) was greater (<i>p</i> = 0.034) than those fed CG (26 kg DM/d), but no differences were observed in milk production (<i>p</i> = 0.557) or enteric CH₄ emission intensity (g/kg milk, <i>p</i> = 0.387). Enteric CH₄ emissions tended to be greater in SH-fed cows (484 g/d) than CG-fed cows (456 g/d; <i>p</i> = 0.075), and N excretion was significantly greater in SH than CG cows (<i>p</i> < 0.001). No mayor shifts in ruminal microbiota or overall ruminal environment were observed. In conclusion, SH can partially replace CG in diets of lactating dairy cows without affecting production, but potential negative environmental impacts should be considered.