A study was made of the role of plant and microbial enzymes in the major nitrogenous changes during ensilage. Perennial ryegrass was ensiled directly, after gamma-irradiation, and after inoculation of the sterile grass with homofermentative lactobacilli. Plant enzymes mainly were responsible for proteolysis, whereas amino acid metabolism was the result of microbial activity. Inoculation reduced proteolysis: this was considered to be a result of rapid acidification. Lactobacillus plantarum and Streptococcus faecalis were shown to be non-proteolytic species with a limited ability to catabolise amino acids. Substantial quantities of water-soluble carbohydrates were made available during ensilage.

U S 1993. Enterobacteria were isolated from grass and silages and identified by the API 20E system. T h e effects of various ensiling treatments on their numbers and types were determined. T h e enterobacteria appear to follow a pattern of succession. Erwinia herbicola and Rahnella aquitilis dominated on fresh grass b u t after ensiling were rapidly superseded by Hajnia alvei, and finally Escherichia coli. Serratia fonticola may appear early on if the p H falls very rapidly.

The effect of pH on plant protease activity was investigated ysing bufered, gamma-irradiated aqueous extract of ryegrass Lolium multiflorum. Rapid protein breakdown occurred in the first f e w days but was followed by a longer period of reduced activity. The overall pH optimum for ryegrass proteases was between 5.0 and 7.0 but there was still considerable activity at the acid pH levels found, eg in silage. Proteolysis did not proceed to completion even when the pH was not inhibiting.

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