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A microbiological screening procedure was used to assess the potential of each of the straight chain members of the series of fatty acids, formic to lauric inclusive, as silage additives. Thirty-four pure cultures of microorganisms were subjected to serial dilutions of each of the acids in broth buffered at unit pH intervals between 3 and 6 inclusive. All the fatty acids of the series appeared to have potential; the lower members (C,-C,) prevented the growth of spore-bearing bacteria and the higher acids had more general antimicrobial effects. A consistent feature of the data obtained was the increase in antimicrobial activity with a decline in pH.

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Some food preservatives, cold sterilants and specific antimicrobial agents were tested against a range of microorganisms at pH 3,4,5 and 6 in a semi-micro assay. The antimicrobial spectra obtained indicated that several of the components might be useful as silage additives. Lactic acid appears to have potential but only when the feed is kept anaerobic as it affords no protection against the activities of yeasts and moulds. Potassium sorbate might have wider application for increasing the aerobic stability of silage, whilst sodium nitrite appears to have application for restricting or suppressing fermentation in silage. The use of sodium ben-roate is unlikely to be economic. Formaldehyde and paraformaldehyde would appear to have great potential in the production of non-fermented silage, whereas the relatively high quantities of hexamine and propylene oxide which are required make these chemicals unattractive. The antibiotic pimaricin appears to have potential as an agent for preventing aerobic degradation of silage and the synthetic antimicrobial agent Bronopol for preventing the activity of sporebearing bacteria. Although it appears that tylosin could be used to prevent bacterial growth the quantity required is, for an antibiotic, quite large.