The effect of formic acid with formalin on grass silage fermentation and the performance of dairy cows

In the first experiment, perennial ryegrass with dry matter (DM) 260 g/kg and water-soluble carbohydrate (WSC) 140 g/kg DM was harvested as first-cut material on 25 May 1982. It was pre-wilted for 24 h prior to ensilage and treated with either a formic acid with formalin additive (WFF) at 4 1/t or no additive (W) and ensiled in two adjoining covered 150 t bunker silos. Subsequently, both silages were satisfactorily fermented. Nevertheless, the pH, ammonia-N g/kg N and lactic-acid content were significantly lower and the residual WSC content significantly higher for WFF than W. Each silage was subsequently individually fed to ten Friesian and ten Holstein dairy cows, together with 10 kg/d of a compound feed containing 160 g/kg crude protein in a 70 d feeding trial. Additive treatment had no significant effect upon silage DM intake, milk output or composition. However, the daily liveweight losses of cows given WFF-treated silage were significantly higher than those given W. In the second experiment, perennial ryegrass (DM 180 g/kg and WSC 170-200 g/kg DM) harvested as first-cut material on 2 June 1983, was either cut and picked up within 20 min of cutting and treated with either the formic acid with formalin additive at 4 1/t (NWFF) or no additive (NW); or wilted for a maximum of 24 h and treated with either the formic acid with formalin additive at 4 1/t (WFF) or no additive (W). Wilting significantly increased subsequent silage DM. The pH of NW was significantly less than W, whilst the ammonia-N g/kg N of NWFF was significantly less than NW and W and that of W significantly higher than the other treatments. Additive treatment significantly increased the residual WSC content. Each silage was subsequently individually feed to 12 Friesian and 12 Holstein dairy cows together with 10 kg/d of a compound feed to 12 Friesian and 12 Holstein dairy cows together with 10 kg/d of a compound feed containing 160 g/kg protein in a 180 d feeding trial. The silage DIM intake of WFF was significantly higher than NW. Silage treatment had no significant effect upon milk output or composition. The daily liveweight loss of cows given WEE-treated silage was significantly less than the other treatments, and the cows on NW had a significantly longer calving index than the other treatments. It is concluded that compared with non-additive-treated silage, formic acid with formalin applied at ensilage produced better fermented silage which, when subsequently given to lactating dairy cows, produced no significant increase in daily silage DM intake, milk output or composition, but had small significant effects upon liveweight change. (C) 1998 Silsoe Research Institute.