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A significant effect of year on maize nutritive value has been reported in many studies; however, the direct effect of year on both nutritive values and fermentation traits of maize silage has not been directly investigated. During a 7-year period (2006-2012), we investigated the following variables of 597 maize silages commercially produced in bunker silos on farms in the Czech Republic: dry-matter content (DM), crude protein (CP), starch, amylase-treated neutral detergent fibre ( aNDF), acid detergent fibre (ADF) and net energy lactation (NEL), as well as fermentation traits such as pH, contents of lactic acid (LA), acetic acid (AA), butyric acid (BA) and the ratio between LA and volatile fatty acids. The effect of year and DM explained 16 and 30% of the variability in nutritive and fermentation traits respectively. Although a common silage DM content was used for each year, the climatic effect of year significantly changed almost all tested variables, but particularly aNDF, ADF, starch, AA and BA. The year contribution to trait variability effect was as much as two times higher for fermentation traits (12·6%) as for nutritive value (6·1%). Temperature-precipitation relationships associated with achieved maize yield were considered as factors explaining the year effect. Temperature and precipitation averaged over the full vegetation period had low relevance to nutritive and fermentation traits. This study reveals the importance of year-to-year variation in silage nutritive value and fermentation, which could be useful for understanding the contribution of year to these changes in both field experiments and national assessments. [ABSTRACT FROM AUTHOR]