Mean retention time in digestive tract and digestion of fresh perennial ryegrass by lactating dairy cows: influence of grass maturity and comparison with a maize silage diet

absorption digestive dairy cows digestion digestive absorption duration ensilado ensilage (produit) feed grasses forraje verde fourrage vert green feed lactation lolium perenne madurez maturity nutritive value rebrote regrowth repousse silage unrestricted feeding vacas lecheras valeur nutritive valor nutritivo zea mays