A major difficulty in producing detailed rations for ruminants, where grass silage is offered ad libitum lies in the accurate prediction of silage intake. It is well documented that ammonia and increased levels of acetic, butyric, caproic and valeric acids in grass silages have negative effects on intake, whilst increased organic matter digestibility has a positive effect. (Gill, Book and Thiago, 1988). A laboratory assessment of silage fermentation characteristics is usually determined from freshly cored samples. Depending on the stability of the silage, and the feeding method, results of such assessments may not be indicative of the silage on offer to stock.

A laboratory method of determining the aerobic stability of silage has been developed by ADAS at Slough Laboratories between 1988 and 1990, (Brooks 1990).