Effects of distiller's dried grains with solubles on enteric methane emissions in dairy and beef cattle: a meta-analysis

Introduction: Distiller's dried grains with solubles (DDGS), a by-product of grain fermentation for ethanol production, are extensively used in livestock feed. Given their nutrient composition, DDGS could potentially influence methane (CH4) emissions, a significant greenhouse gas concern in ruminant production systems. This study utilized a multilevel random-effects meta-analysis to assess the impact of DDGS inclusion in cattle diets on CH4 production and yield. Methods: The literature search was conducted on 23 July 2024. Studies reporting CH4 emissions and dry matter intake (DMI) in cattle fed DDGS-based diets were identified, and data extraction was performed. The meta-analysis calculated the mean difference (MD) for DMI and CH4 yield and the relative mean difference (RMD) for CH4 production across the selected studies. Results: A total of k = 25 effect sizes from 10 studies were included in the DMI meta-analysis. DDGS had no significant effect on DMI in dairy or beef cattle (p = 0.770, MD = 0.070, 95% confidence interval [CI] from -0.420 to 0.561). For CH4 production, k = 24 effect sizes from 10 studies were analyzed, revealing no significant effect (p = 0.759, RMD = -1.045, 95% CI: from -8.025 to 5.935). Similarly, the meta-regression model indicated that the diet's ether extract (EE) had no significant influence (p = 0.815, 95% CI from -1.121 to 1.409) on CH4 production. For CH4 yield, k = 23 effect sizes from 10 studies were included, with results showing no significant effect (p = 0.475, MD = -0.434 g/kg DMI, 95% CI: from -1.673 to 0.805). The regression model for the EE content of the diet also showed no significant impact on CH4 yield (p = 0.311, 95% CI: from -0.366 to 0.122). Discussion: The findings suggest that the inclusion of DDGS does not significantly affect DMI, enteric CH4 production, or CH4 yield in cattle. Moreover, the EE content in DDGS-containing diets does not significantly influence CH4 outcomes. These results indicate that DDGS can be incorporated into cattle diets without exacerbating CH4 emissions, contributing to sustainable livestock feeding practices.