Relationship between the Quality of Italian Ryegrass Silage and the Presence of Phages for Silage-Making Lactobacilli

Forty-one samples of Italian ryegrass silage were examined for the presence of phages in silage-making lactobacilli. For the detection of phages, 94 strains of Lactobacillus plantarum and five strains of L.casei, all of which were newly isolated from silage, five type strains of L. plantarum, three type strains of L.casei, and five commercially available strains were used. Only ten samples (24% of the silages) had phages. More than 45% of the strains tested, all L. plantarum, were infected by phages. Samples in which phages were detected usually were moist, had a high pH, and produced little lactic acid. In silages with pH 4.1 or below, no phages were detected. The higher the moisture content, the greater was the possibility of phage infection. The results showed that contamination by phages deteriorated the quality of the silages, and that phage control is needed.