In many areas of the U.S., maintaining ideal environmental conditions, including water quality, are major issues facing commercial livestock operations. However, the cost of not maintaining a nutrient balance on a dairy farm isn’t just environmental – but also economic.
An increase in nitrogen efficiency of milk production represents a decrease in the amount of nitrogen unused by the cow. Work by various researchers indicates only about 25 percent of the nitrogen intended for the production of milk and milk components is used for that purpose, and the rest is excreted from the cow. When we compare the cost of providing energy versus protein to the cow ($ per unit of nutrient), we know it is more expensive to meet the cow’s protein requirement than it is to meet its energy requirement.
How do we then use the diet to improve nitrogen efficiency? Part of the reason we have historically overfed nitrogen was our limited ability to define animal requirements but also to adequately quantify the amount and availability of nitrogen coming from feed ingredients. As a result, we have included a safety cushion in our diets by over-formulating for protein.
This practice allowed us to meet the cow’s requirements to the best of our ability but also caused the efficiency of nitrogen use for production to decrease. Our ability to characterize feed ingredients and model cow requirements has greatly improved in the last 15 years.
For example, because we routinely analyze alfalfa haylage for the various protein fractions rather than only crude protein (CP), we are able to determine how much of that CP is degradable in the rumen and available to rumen microbes. Conversely, we will know how much of that CP is not degradable in the rumen and will either pass through to the small intestine for digestion or pass out of the cow completely. In the past, when we might have balanced a diet using 18.5 percent CP (dry matter [DM] basis) for haylage, we only had a rough idea of how much protein would be degraded in the rumen.
With limited information, it was more difficult to maximize the efficiency of nitrogen use for production. This is because we weren’t able to accurately quantify how much of the protein was being used at each location along the digestive tract or also determine how much protein our cows required for a given production level and stage of lactation. To make sure we had all of our bases covered, many nutritionists added that over-formulation safety cushion.
In many cases, there was over-supplementation of protein, and more feed may have been purchased than necessary. Because we want to take full advantage of current capabilities and reduce the need for the over-formulation safety cushion, this highlights the importance of regularly analyzing our feed ingredients to better quantify all of the nutrient fractions necessary to balance for maximum nitrogen efficiency.
Past research tells us milk nitrogen efficiency declines with increasing CP intake. In the same paper, results indicated within a range of dietary CP (approximately 14 to 19 percent, DM basis), milk yield and milk protein composition were not affected. A published meta-analysis of past research concluded milk nitrogen efficiency for the lowest-CP diets was greater than the diets with the greatest CP concentrations (36 percent versus 25.4 percent, respectively).
Furthermore, the same analysis reported studies demonstrating an increase in milk and milk protein yields apparently due to increasing dietary CP were caused by a concurrent increase in dry matter intake (DMI). This information suggests it is very possible to maintain the same level of production while reducing total dietary protein concentrations.
Research also indicates decreasing dietary crude protein by itself has a greater effect on improving the nitrogen efficiency of milk production than increasing milk yield. Most of the above improvement in the efficiency of nitrogen used for milk production was accomplished by reducing total dietary CP without a negative effect on milk production.
This was achieved by balancing diets to provide fermentable carbohydrates that allow the rumen microbes to decrease rumen ammonia concentrations and use it for their own protein production – then balancing to meet specific amino acid requirements of the cow after the microbial contribution.
So what is the economic benefit of improving the cow’s milk nitrogen efficiency? In a five-year study published a little more than 10 years ago, a commercial dairy being observed was able to increase nitrogen efficiency on their farm by 24 percent through a combination of increasing forage concentrations in the diet, balancing their diets for metabolizable protein and for specific amino acid requirements rather than total CP. Using feed prices at the time the paper was published, these changes resulted in approximately 60 cents per head daily purchased feed cost savings.
Again, this information isn’t new, but if your rations are not already formulated to maximize nitrogen use efficiency, maybe it’s time to have that conversation and take advantage of a gain in efficiency and, potentially, profit for your dairy. If you’re unsure of where to start, one place may be milk urea nitrogen (MUN).
Although MUN will not tell you what is causing the inefficiencies, it can tell you if your cows are getting too much nitrogen or not enough. Yes, there are several factors that affect MUN concentration, but dietary protein is the major one. In general, if your herd is experiencing MUNs greater than 12 milligrams per deciliter, your herd is likely consuming more protein than it needs. 
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Benjamin Pamp
- Dairy Technical Specialist
- Cargill
- Email Benjamin Pamp
