A total of 4224 samples of silage made in bunkers on commercial farms between 1987 and 1993 was analysed to investigate the ef fect of dry matter (DM) content and silage additives on fermentation as measured by ammonia-N concentration and pH . Increasing DM content without additive use had a major beneficial influence on fermentation . When silage DM contents were greater than 240 g / kg at least 70% of the silages were well fermented . Below this , with diminishing DM concentration , the proportion of well fermented silages declined so that with DM below 180 g / kg only 14% were well fermented .
The benefit of silage additives was extremely variable . Below DM concentrations of 200 g / kg , formic acid and formic acid based additives improved the proportion of well fermented silages , compared with non-additive-treated silages , by about 50% . Similarly , acid with formalin use provided 40% improvement and inoculant additives provided 16% improvement . Acid mixtures , inorganic acids , salts , enzymes , sugars and absorbents provided little or no benefit compared with non-additive-treated silages .
Above DM 200 g / kg the benefit of formic acid and acid with formalin additives in terms of improving the proportion of well fermented silages , compared with non-additive-treated silages , declined with increasing DM from about 30% units increase in the DM range 200 -220 g / kg , to only 2% increase for silages with DM above 300 g / kg . In contrast , over 90% of silages treated with formic acid based additives were well fermented irrespective of DM content . In the DM range 220 -280 g / kg inoculants improved the propor- tion of well fermented silages compared with nonadditive-treated silages , by about 15 -20% . Above this DM they provided a small improvement of about 5% .
The limited number of other additive-treated silages suggested that irrespective of silage DM , enzymes provided a small but variable improvement in fermentation , compared with non-additive-treated silages ; whilst acid mixtures , inorganic acids , salts , sugars and absorbents conferred no consistent benefit .