A total of 1009 samples of silage made in bunker silos on commercial farms between 1972 and 1978 was analysed to investigate the effect of herbage water‐soluble carbohydrate content (WSC) and weather conditions at ensilage on fermentation as measured by ammonia‐N concentration and pH of first‐cut grass silages. Silage dry matter (DM) content had the major effect on fermentation. Factors influencing silage DM were rainfall and hours of sunshine during silage making, and DM content of the grass cut. WSC content of herbage ensiled also had a significant effect on subsequent fermentation. The major influences on herbage WSC were hours of sunshine and rainfall during the growing season. The effect of chemical additives, albeit at poorly defined and often inadequate rates, was small in comparison to that of silage DM. The minimum DM necessary to produce well‐fermented silage without additive was approximately 260 g kg−1. Use of formic acid significantly reduced this requirement to 240 g kg−1 and to 252 g kg−1 for sulphuric add + formalin. The results indicate that the minimum herbage WSC necessary to prevent a clostridial fermentation developing in silage with a DM content of 230 g kg−1 is approximately 37 g kg−1 without additive and 30 g kg−1 with formic acid. It is concluded that on commercial farms, weather conditions i.e. amount of rainfall and sunshine prior to and at ensilage, have a greater effect on subsequent silage fermentation than additive use.

Data from thirty-three experiments conducted at three ADAS Experimental Husbandry Farms were used to compare unwilted non-additivetreated silage with silage treated with formic acid, a formalin and formic-acid mixture, a calciumformate and sodium-nitrite mixture, a formalin and sulphuric-acid mixture and wilted silage made without or with formic acid or a formalin and formic-acid mixture.Formic acid significantly reduced pH and wilting significantly increased silage pH compared with other treatments. Formalin-acid mixtures significantly reduced pH compared with untreated silage. Formic acid in conjunction with formalin or wilting significantly increased watersoluble carbohydrate in silage compared with other treatments except wilting. Formic acid either alone or combined with either formalin or wilting significantly reduced silage butyric acid content compared with other treatments. Formic acid treatment either alone or combined with formalin significantly increased lactic acid as a proportion of total silage acids compared with other treatments except sulphuric acid-formalin.All treatments significantly increased silage dry matter (DM) intake compared with untreated silage and intakes of wilted silage were significantly greater than of unwilted silage. Daily

Dry matter (DM) contents of 205 silages were determined by toluene distillation and oven drying at 100°C. The toluene distillation method gave values up to 11 % higher than the oven drying method, the largest differences occurring with silages of high volatile fatty acid concentration, low lactic acid concentration and high ammonia nitrogen content expressed as a percentage of total nitrogen. Highly significant (P< 0.01) correlations were shown between toluene dry matter and oven dry matter for various ranges of ammonia nitrogen, and equations are presented which allow toluene dry matter to be readily estimated on a routine basis for grass silage.

A total of 1713 samples of silage from commercial farm silos were analysed to investigate the effect of dry matter (DM) content and chemical additives on fermentation as measured by ammonia-N concentration and pH, Increasing DM content without additive use had a major beneficial influence upon fermentation. When silage DM contents were greater than 260 g kg~' 83% of silages were well fermented, with average ammonia-N concentrations of 94 g (kg total N)"' and pH 4 36, With diminishing DM concentration the proportion of well fermented silages declined. In the DM range 220-260 g kg"' 67% of silages were well fermented with ammonia-N concentrations of 125 g (kg total N)-' and pH 4 30, in the DM range 180-220 g kg"' 48% were well fermented with ammonia-N at 151 g (kg total N)~' and pH 4 38 and with DM below 180 g kg"' no silages were well fermented with ammonia-

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