Growth of naturally occurring Listeria spp. in silage: a comparative study of laboratory and farm ensiled grass

A laboratory method for ensiling grass in bags, which simulates the aerobic deterioration found in big bale silage, is described. These conditions selectively encouraged the multiplication of naturally occurring listeria. All grasses ensiled in this way gave detectable numbers of listeria, usually L. monocytogenes, indicating that these bacteria are a normal part of the microflora of grass. The results from the laboratory silage were comparable to those found in the same grass ensiled in big bales on the farm.