Dried Distillers' Grains with Solubles in Ruminant Diets: Effects on Enteric Methane Emissions and Production Responses-A Systematic Review.

Enteric methane (CH4) emissions from ruminants contribute to agricultural greenhouse gas emissions and represent a loss of dietary energy that could otherwise support animal production. Dried distillers' grains with solubles (DDGSs) have received increasing attention as an alternative feed ingredient because of their nutritional value and potential to influence rumen fermentation, nutrient utilization, and CH4 emissions. This systematic review evaluated the effects of DDGSs on enteric CH4 emissions and nutrient utilization in ruminant diets. Literature searches were conducted in Google Scholar, Scopus, and Web of Science for studies published between 2010 and 2025. Following PRISMA guidelines and using the SYRCLE risk of bias tool, 17 studies, comprising 9 in vivo, 5 in vitro, and 3 integrated in vivo-in vitro studies, were included in the qualitative synthesis. The DDGS supplementation did not consistently reduce absolute CH4 production, although reductions in CH4 yield and emission intensity were more frequently reported. Moderate inclusion levels (up to 20% of diet dry matter) were frequently associated with improved nutrient utilization, feed efficiency, and animal performance, although these responses varied among studies. Reductions in CH4 yield and emission intensity were more commonly reported than reductions in absolute CH4 production. Higher inclusion levels (>30% of diet dry matter) produced more variable responses and were often associated with reduced fiber digestibility. In conclusion, the available evidence suggests that DDGS may act as a dietary modifier capable of improving nutrient utilization and production efficiency under appropriate dietary conditions; however, responses remain dependent on inclusion level, DDGS source, basal diet composition, and production system.