Abstract
A low nitrogen utilization efficiency (NUE, the ratio of retained N to N intake) and high methane (CH4) emissions of ruminants can lead to potentially high diet protein wastage and directly contribute to global warming. Diet manipulation is the most effective way to improve NUE or reduce CH4 emissions. This study investigated how replacing oat hay with alfalfa hay (AH) or common vetch hay (CVH) with different proportions (20% (20) and 40% (40) of the total dry matter (DM) allowance) affects the body weight gain (BWG), NUE, and CH4 emissions of crossbred Simmental cattle. The forage dry matter intake (DMI) and the total DMI of cattle fed on a CVH40 diet were significantly higher than the values for those fed on AH20 or AH40 diets (p < 0.05). There were no differences in the BWG for the four treatments observed, however, nutrient digestibility significantly decreased in the AH40 diet as compared with the AH20 diet (p < 0.05). The NUE was significantly lower in AH40 than in CVH20. The CH4 emissions were significantly lower for the CVH40 diet than with the AH20 diet (p < 0.05). Our findings suggest that a 20% AH and 40% CVH substitution for oat hay are the optimal proportions to maintain the BWG, NUE, nutrient digestibility, and reduce the CH4 emissions of crossbred Simmental cattle. Overall, CVH has a greater potential to reduce CH4 emissions than AH.