Sustainable grazing systems often encompass the use of forage legumes with the aim of reducing input of fertilizers and supplements, thanks to their high nutritive and feeding value. However, the incorporation of legumes at high proportion in sheep diet can exacerbate the unbalance between energy and protein and hence increases the release of N to the environment via urine, fecal and milk. Grazing of immature pastures (winter-spring) that have high protein content (>25%) and low fiber and tannin content results in high milk urea (>50mg/100ml). The same applies for N fertilized pastures that must be avoided. In this regard pastures must be monitored for protein content. In order to keep milk urea in optimum levels, ration must be formulated with a protein and energy content according to animal requirements. Excess protein content and protein intake must be avoided. Diets rich in degradable proteins or soluble nitrogen in rumen that do not contain sufficient amounts of non-structural carbohydrates for energy supply to rumen microorganisms for microbial protein synthesis, such as early stage hay crops, will result in excess protein or unabsorbed protein, increased urea synthesis and excretion via milk and manures. Milk urea level measurement it’s easy to be implemented in the flock with commercial diagnostics kits. Flock should be regularly monitored for milk urea levels during the lactation period either individually or from the tank. When high urea levels (>50mg/100ml) found cereals and fibre feeds (i.e straw) must be added in sheep rations and their energy and protein content must be measured and corrected. High urea levels (>60mg/ml) could lead to alkalosis, reproductive disorders, as well as to embryonic loss. Therefore, optimising the use of milk urea as a management tool on dairy farms, also during the grazing season, could reduce N losses to the environment, while maintaining productivity and ensure animal health.