Effect of silage characteristics on enteric methane emission from ruminants.

Abstract This review evaluates the effects of silage characteristics on enteric methane (CH 4 ) emission from ruminants by performing a meta-analysis. A total of 17 studies were selected from the literature, and the relationship between CH 4 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 (%; R 2 =0.74) and crude protein content (g/kg DM; R 2 =0.36) were negatively associated, and neutral detergent fibre (NDF) content (g/kg DM; R 2 =0.44) was positively associated with CH 4 yield. This indicates that increased grass silage quality consistently decreases CH 4 yield and may be an effective enteric CH 4 mitigation strategy. Similarly, optimizing maize silage quality appears to be an effective enteric CH 4 mitigation strategy, because NDF content (g/kg DM; R 2 =0.60) was positively associated with CH 4 yield. Upon replacing grass silage with maize silage, dietary starch content (g/kg DM; R 2 =0.62) and silage replacement level (%; R 2 =0.33) were negatively associated, and NDF content (g/kg DM; R 2 =0.34) was positively associated with CH 4 yield. These results indicate that replacing grass silage with maize silage consistently decreases CH 4 yield and may be an effective enteric CH 4 mitigation strategy. In contrast, replacement of alfalfa silage with maize silage was not associated with CH 4 yield and does not appear to be an effective strategy to decrease CH 4 yield. In conclusion, management practices to improve silage quality are a potent mitigation strategy to reduce enteric CH 4 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.