RESEARCH NOTE

Abstract Data from twenty‐two experiments conducted at tour ADAS Research Centres during 1980–92 were used to compare untreated silages with silages treated with formic acid, with or without added formalin, commercial inoculants or molasses. The sillages were made from herbage whose dry‐matter (DM) and water‐soluble carbohydrate (WSC) contents were 277 (s.e. 0.46) g DM kg−1 and 36 (s.e. 8.1) g kg−1 respectively. Inoculant use significantly decreased silage pH and ammonia‐N, significantly increased lactic acid and total acid content, and decreased butyric acid and total short‐chain fatty acids. Formic acid use significantly increased silage lactic acid and total acid content, and decreased butyric acid content, whereas formic acid+formalin significantly decreased silage ammonia‐N level. Molasses had little effect upon silage fermentation. Improvements in silage fermentation, however, produced little benefit in terms of either silage DM intake or liveweight gain when the silages were offered to growing lambs. It is suggested from the results that inoculant‐ and formic acid‐based additives can be used to improve the fermentation of big‐bale silages.