Variations with breed, age, season, yield, stage of lactation and herd in the concentration of urea in bulk milk and individual cow's milk

age alimentation breeds (animals) composition globale contenido proteico cows edad feeding hatos herds lactation lait leche milk milk yield protein content proximate composition race (animal) razas (animales) rendement laitier rendimiento lechero troupeau urea uree vaca vache