Sources of variation in nutritive values of tropical forages from the Caribbean

The chemical composition, in vitro digestibility with rumen liquor and agricultural factors (age of regrowth, season, level of fertilization) of 1313 tropical forages from various islands of the Caribbean and of La Re´union were recorded in a database. The nutritive values were expressed in the French unit system, i.e. digestible energy, metabolizable energy, net energy for lactation, net energy for maintenance and growth, protein digestible in the small intestine supplied by rumen-undegraded dietary protein (PDIA), protein digestible in the small intestine supplied by microbial protein from rumen-fermented organic matter (PDIME), protein digestible in the small intestine supplied by microbial protein from rumen-degraded dietary protein (PDIMN), and voluntary dry matter (DM) intake by sheep (VDMIs), dairy cows or growing cattle. Digestibility of DM and OM and voluntary DM intake were determined with regression equations fitted to tropical data previously reported. The age of regrowth and the type of forage were the main sources of variation, whereas the country, season and level of nitrogen fertilization had no important effect on energy or protein values. Mean nutritive values are given for each type of forage and age of regrowth after correction for the level of nitrogen fertilization, season and country.