Abstract: Building on the concept and definition of the Food Equivalent Unit, this paper modifies the original definition by including energy and protein digestibility for calculation of the forage food equivalent unit (FEU). Using 1 kg alfalfa as the forage standard (FEU=1.0 with standard edibility (100%), standard moisture content (10%), total energy (14.267 MJ·kg^-1), crude protein (229 g·kg^-1 DM), digestible DM (65.48%), feed standard energy and protein factors are derived and, together with digestibility values, used in the model to calculate FEU of other forage types. The FEU is proposed as a measure of the feed value of forage resources such as native grassland, cultivated forage, silage and cereal straw. The results indicate that the average FEU of all principal forage types in China is in the range of 0.2-1.2 FEU·kg^-1, and the FEU of leguminous forage (with good energy and protein content) is between 0.4-1.2 FEU·kg^-1. The FEU of Leucaena chinensis, of which the leaves have high digestibility, is 1.2 FEU·kg^-1; the FEU of grass species ranges from 0.2-1.0 FEU·kg^-1, with FEU of perennial ryegrass in the warm season being 1.0 FEU·kg^-1, and FEU of silage about 0.1-0.7 FEU·kg^-1. The FEU of straw is about 0.2 FEU·kg^-1. The FEU production capacity of 21 major natural grassland types (e.g.: desert steppe and alpine meadow) in summer growing season was calculated to be in the range 142-2739 FEU·ha^-1, with alpine meadow in Maqu, and Hebei’s meadow steppe grassland both being above 1300 FEU·ha^-1. The forage FEU has the potential to be used as a quick and easy-to-calculate-and-interpret measure of forage feed value of both arable and pastoral forage and feed crops, and as such, to be a valuable management tool in the selection of forage crops for livestock production.

Key words: grassland agro-ecosystem, forage, silage, livestock, digestibility, metabolic energy, crude protein, feed value, grassland evaluation