LACTIC-ACID FERMENTATION IN SILAGE PRESERVED WITH FORMIC-ACID

A study has been made of silages preserved with formic acid (4.6 g kg(-1)), in which the content of residual sugar in the aqueous phase was at least 10 g l(-1), thus permitting lactic acid fermentation. The mean (+/- SD) pH of the direct-cut silages was 3.87 +/- 0.21. The factors studied accounted for most of the variation in silage acidity. In lactic acid fermentation in silage, 0.20 g acetic acid, 0.031 g ammonia-nitrogen and 0.090 g soluble nitrogen are produced with each gram of lactic acid, and 1.8 g reducing sugars are consumed. The other silage microorganisms, referred to here as spoilage microorganisms, also produce acetic acid, ammonia-nitrogen and soluble nitrogen. The production of acetic acid by the spoilage microorganisms is largely independent of the degradation of protein. For every gram of acetic acid produced by spoilage microorganisms, 3.6 g of sugar are consumed; the production of ammonia-nitrogen and soluble nitrogen does not result in a loss of sugar. For the ionisation of the amino acids released in protein degradation, 2.3 g of lactic acid are required for each gram of amino acid nitrogen. A surprising result was that the production of acetic acid increases that of lactic acid by 0.55 g for each gram of acetic acid, whereas the production of ammonia does not increase the content of lactic acid in well preserved silage. This study is based on the analysis of 61 036 silage samples which the farmers have sent to the silage laboratories.