AbstractA total of eighty‐nine big‐bale (BB) silages made on commercial farms in South Wales during the autumn in 1983‐87 were analysed to discern the effect of dry matter (DM) content on fermentation. Silages were made predominantly in late September, during fine weather from permanent pasture or perennial ryegrass pastures, which had not been grazed for 9 weeks. On average 7·8 ha of pasture were cut; most farmers attempted to pre‐wilt grass for an average of 36 h prior to ensilage in individual plastic bags. Silage making was usually completed within 4 d of starting to cut. Silage ammonia‐N content was inversely correlated with DM content. The results indicated that a DM content of about 280 g kg−1was needed to produce well‐preserved silage with an ammonia‐N content of 100 g (kg total N)−1. Silages were, therefore, generally poorly preserved because the DM increase from wilting was