The role of dietary protein in the nutrition of the dairy cow and overall farm sustainability can be summarized as: (1) effects on dry matter intake (DMI), milk yield, and milk composition, (2) effects on feed costs, (3) environmental effects, and (4) possible effects on reproduction efficiency. Historically protein has been fed trying to satisfy requirements in term of CP, both in percentage of D.M. or grams per cow per day, and more recently we passed to the concept of metabolizable protein and amminoacids. Basically when we are feeding cows we have to be aware that we are feeding a portion of protein available for the microorganism in the rumen (RDP) and a portion of amminoacids that will by-pass the rumen and will be absorbed in the gut (RUP). The balance between this two fractions is crucial in maximizing cow’s performance. Thus the two questions we have to ask our self when balancing diets in terms of protein are: are we providing the proper RDP to maximize microbial protein production in the rumen? Are we feeding enough amminoacids to maximize milk and protein production?

This balance is strictly linked to the concept of milk nitrogen efficiency (MNE). If we can optimize the protein fed to the cows, we can consequently improve the efficiency of the latter. MNE is basically the ratio between nitrogen in the milk and nitrogen fed to the cows. Theoretically the efficiency limit of nitrogen in dairy is 40-45%, in the reality this value range from 25% to 28% depending on the region you are considering. To optimize MNE we have to avoid excesses and deficiencies in protein nutrition. Feeding diets with lowered protein content reduces nitrogen input, improves nitrogen utilization efficiency, and reduces nitrogen losses from manure. Reducing dietary protein also benefits the producer by reducing feed cost and improving overall farm profitability. There are many examples where decreasing protein concentration in dairy diets dramatically decreased manure nitrogen losses without affecting animal production. These interventions, however, have to be balanced with the risk of loss in milk production. If the true animal requirements for metabolizable protein are not met, long-term production cannot be sustained.

Today there are many tools available on the market designed to improved nitrogen efficiency and cow’s performances. Slow release non protein nitrogen is able to increase microbial protein production at rumen level and represent a valuable source of RDP. On the other side encapsulated amminoacids as methionine and lysine, can reduce typical deficiencies in dairy cow nutrition. These two amminoacids are indeed the first and second limiting amminoacids in dairy cow, meaning that a shortage in these two will compromise milk production and protein yield.

These two nutritional strategies are in conclusion able to improve MNE and reduce the environmental impact relative to nitrogen.