Causes of variation in fatty acid content and composition in grass and maize silages

The aim of this study was to quantify the variation in fatty acid (FA) content and composition in grass and maize silages and to identify key management factors during plant growth and the ensiling process that cause this variation. Samples of grass (n=101) and maize (n=96) silages were randomly collected from commercial dairy farms in The Netherlands in 2007 and 2008. Multivariate analysis was computed on data related to agronomic conditions, harvest-maturity, wilting management (grass only), chemical composition and feeding value of the individual silages to search for variables which cause the variation in FA contents. Total FA content was highly variable in grass (8.10–32.47g/kg DM) and maize (12.37–35.25g/kg DM) silages, and contents of all major individual FA also had a high variation. The content of C18:3n-3 had large variation (3.57–20.53g/kg DM) in grass silages, while C18:2n-6 had large variation (6.89–22.41g/kg DM) in maize silages. Redundancy analysis (i.e., a combination of principal components analysis and multiple regression) showed that variables related to plant maturity at harvest explained most of the variation in FA content, with silages from young grass and young maize having high contents of C18:3n-3. Plant cell wall components and digestibility are related to the maturity at harvest and were strong predictors of the FA contents in grass and maize silages. Regression equations based on nutrient composition provided relatively good estimations of the contents of C18:3n-3 (R²=0.73) and total FA (R²=0.65) in grass silages. Regression equations based on nutrient composition and feeding values gave relatively good estimations of the contents of C18:2n-6 (R²=0.51) and total FA (R²=0.48) in maize silages. Bruising (i.e., removing of the waxy layer of leaves and stem), silage pH and ammonia–N content did not affect the FA content in the grass silages.