The feedstock was provided by Wykey Farm, Shrewsbury, UK. The 16-week-old CM was stored outside while the maize, which had been harvested 12 months previously, was ensiled. After visual inspection and removal of any non-biodegradable contaminants the feedstock was homogenized by a macerating grinder (S52/010 Waste Disposer, IMC Limited, UK), packed into plastic storage bags and frozen at 18 C. The frozen feedstock was thawed before use and stored at 4 C for a maximum period of one week.