The effects of the rate of addition of formic acid and sulphuric acid on the ensilage of perennial ryegrass in laboratory silos

Abstract

AbstractPerennial ryegrass was ensiled in laboratory silos after addition of formic acid (850 g kg−1) or sulphuric acid (906 g kg−1) at rates of 0, 2, 4 and 6 litres t−1 fresh grass. Silos were opened after 6, 18 and 90 days and the silage subjected to chemical and microbiological analysis. The untreated control was poorly fermented with a final pH of 4.7, a butyric acid concentration of 19 g kg−1 dry matter (DM) and an NH3‐N content of 275 g kg−1 total nitrogen (TN). For the formic acid treatments the 2 litre t−1 and 6 litre t−1 levels both produced well‐preserved silages but they were of different types. The silage treated with 2 litre t−1 had a pH of 4.0, a lactic acid concentration of 92 g kg−1 DM and 161 g NH3‐N kg−1 TN, whereas with the 6 litre t−1 treatment, fermentation had been severely restricted. The pH was 4.2, the lactic acid concentration was only 8 g kg−1 DM and the NH3‐N content was 80 g kg−1 TN. However, formic acid at 4 litre t−1 produced a badly fermented silage of final pH 5.0 with lactic acid and butyric acid concentrations of 16 and 15 g kg−1 DM, respectively, and an NH3‐N content of 149 g kg−1 TN. Sulphuric acid at 2 and 4 litres t−1 produced silages of low lactic acid contents, 36 and 24 g kg−1 DM, and they also contained butyric acid in concentrations of 13 and 11 g kg−1 DM; respective NH3‐N contents were 206 and 114 g kg−1 DM. When sulphuric acid was added at 6 litres t−1, despite a reduction in the pH of the grass to 3.5, fermentation was not restricted as it was with the equivalent level of formic acid. Lactic acid was present at 27 g kg−1 DM and the ethanol concentration was very high at 66 g kg−1 DM; the sulphuric acid‐treated silages were characterised by high yeast counts. At the higher rates of addition, formic acid reduced the.