Supplementing Tannins to Increase Performance and Reduce Methane Emissions in Cows Grazing on Western Grasslands

Cattle grazing on U.S. rangelands often rely on a limited diet made up mostly of grasses. As the seasons change from spring to fall, the nutritional quality of these grasses declines, leading to less efficient digestion and higher production of methane—a potent greenhouse gas. In addition, most grass-based pastures lack beneficial plant compounds, such as tannins. This study explored whether adding natural tannins—specifically, condensed and hydrolyzable tannins from quebracho and chestnut trees—to the diet of grazing cattle could improve how the use efficiency of nutrients and reducing methane emissions from cattle. Over two years, 24 cow-calf pairs grazed in small grass pastures, with half receiving a daily feed supplement that included tannins. We measured forage quality, weight gain, methane emissions, and nitrogen excretion in the cows to assess the overall impact of the tannin supplement on cattle health and environmental outcomes. Cows that received tannins had lower levels of blood urea nitrogen and tended to excrete less nitrogen in their urine, suggesting they were using dietary protein more efficiently. This finding is important because nitrogen from urine can contribute to environmental pollution. Although the differences in methane emissions were not statistically significant, cows given tannins consistently produced less methane throughout the study. By the final phase, their emissions were nearly 20% lower than those of cows that did not receive tannins. Cows and calves supplemented with tannins showed consistent trends of improved weight performance relative to non-supplemented animals, aligning with favorable effects on nitrogen use and reduced methane emissions. These results suggest that adding natural plant compounds, like tannins, to the diets of grazing cattle could help reduce the environmental footprint of beef production, especially by improving nitrogen efficiency and potentially lowering greenhouse gas emissions during the cow-calf stage.