Effect of silage characteristics on enteric methane emission from ruminants

This review evaluates the effects of silage characteristics on enteric methane (CH₄) emission from ruminants by performing a meta-analysis. A total of 17 studies were selected from the literature, and the relationship between CH₄ yield (g/kg dry matter [DM] intake) and silage characteristics was determined using a mixed model univariate regression procedure. For grass silage, organic matter digestibility (%; R² = 0.74) and crude protein content (g/kg DM; R² = 0.36) were negatively associated, and neutral detergent fibre (NDF) content (g/kg DM; R² = 0.44) was positively associated with CH₄ yield. This indicates that increased grass silage quality consistently decreases CH₄ yield and may be an effective enteric CH₄ mitigation strategy. Similarly, optimizing maize silage quality appears to be an effective enteric CH₄ mitigation strategy, because NDF content (g/kg DM; R² = 0.60) was positively associated with CH₄ yield. Upon replacing grass silage with maize silage, dietary starch content (g/kg DM; R² = 0.62) and silage replacement level (%; R² = 0.33) were negatively associated, and NDF content (g/kg DM; R² = 0.34) was positively associated with CH₄ yield. These results indicate that replacing grass silage with maize silage consistently decreases CH₄ yield and may be an effective enteric CH₄ mitigation strategy. In contrast, replacement of alfalfa silage with maize silage was not associated with CH₄ yield and does not appear to be an effective strategy to decrease CH₄ yield. In conclusion, management practices to improve silage quality are a potent mitigation strategy to reduce enteric CH₄ emission per unit of feed fed to ruminants, and implications of silage quality have to be addressed when assessing greenhouse gas emissions in ruminant production.