Influence of supplemental dietary copper in high roughage rations on nutrient digestibility and methane emission in Holstein bulls

Feed additives, chemical inhibitors, and biological approaches have been studied and used to inhibit production of enteric methane (CH4) in ruminants by modifying methanogenic bacterial communities. However, information on the potential of micromineral supplements in this regard is limited. The objective of this study was to evaluate the effect of 20 mg (control) and 40 mg Cu (from supplemental CuSO4)/kg dietary dry matter (DM) on nutrient digestion, ruminal fermentation characteristics, and enteric CH4 emissions measured with the tracing technique of sulfur hexafluoride. Six Holstein bulls were divided into two groups of three animals and assigned to one of two experimental diets in a crossover design. Percentages of apparent digestibility of DM, neutral detergent fiber, and N did not differ (P>0.05) between treatments. Supplemental Cu decreased (P<0.001) total tract digestibility of Cu by 25%. There were no differences (P>0.05) between treatments in ruminal fluid pH or, acetate:propionate ratio. Emission of CH4 tended (P<0.1) to decrease by 23% with supplemental Cu. This study showed that 40 mg Cu/kg dietary DM is a feasible dietary level in cattle, because supplemental Cu from CuSO4 did not impair nutrient digestibility and tended to decrease enteric CH4 emissions.