FROM THE FARM REPORT: IMPROVING NITROGEN EFFICIENCY IN DAIRY COWS: GETTING MORE MILK FROM EVERY POUND OF PROTEIN
- Isabela Carrari
- 9 minutes ago
- 3 min read
Protein is one of the most expensive nutrients in a dairy ration, often one of the most overfed. While crude protein (CP) levels of 16 to 18% are still common in many lactating cow diets, research continues to show that a significant portion of that nitrogen isn’t converted into milk protein: Only about 25 to 35% of the nitrogen a cow consumes is captured in milk, with the remainder excreted in manure, particularly in urine (Broderick, 2003; Huhtanen and Hristov, 2009). When excess nitrogen is excreted in urine it’s rapidly converted to ammonia, contributing to air quality issues and nitrogen losses from the farm. At the same time, overfeeding protein increases ration costs without improving production. For farms in the Northeast, where feed costs are high and environmental regulations continue to tighten, improving nitrogen efficiency is a practical way to address both concerns at once.
To understand where these losses occur, it helps to think about how the cow uses protein (Figure 1). Most of the dietary protein isn’t used directly by the animal; instead, it’s first processed by rumen microbes. The portion of the diet known as rumen degradable protein (RDP) is broken down in the rumen and used by microbes, along with energy from carbohydrates, to produce microbial protein. This microbial protein is then digested in the small intestine and provides most of the amino acids used for milk production. The remaining portion, rumen undegradable protein (RUP), bypasses the rumen and is digested later in the intestines. Excess RDP without sufficient fermentable energy leads to ammonia accumulation, with nitrogen absorbed, converted to urea, and excreted, reducing efficiency and increasing costs. Conversely, insufficient RDP limits microbial growth, impairing fiber digestion, intake, and milk yield. While increasing RUP can help supply amino acids directly to the intestine, it’s only effective when overall metabolizable protein requirements are met (NASEM, 2021).
Several studies have found that when diets are properly balanced for amino acids, lowering dietary CP from approximately 17–18% to 15–16% can maintain milk production while reducing nitrogen excretion (Figure 2) (Broderick, 2003; Barros et al.; 2017; Zeleke et al., 2025). This approach requires careful formulation, but can significantly reduce feed costs, especially when protein feeds are expensive.
On many Northeast farms, forage quality largely determines how efficiently nitrogen is utilized. Highly digestible corn silage and haylage provide the fermentable energy needed for microbes to capture nitrogen and produce microbial protein. In contrast, mature, heat-damaged, or inconsistent forages can limit energy supply in the rumen, reducing nitrogen utilization and increasing losses. A practical on-farm
(Adapted from Zeleke et al., 2025).
tool to assess nitrogen use efficiency is milk urea nitrogen (MUN). Values between 8 and 12 mg/dL generally indicate a good balance between protein and energy, whereas levels above 12-14 mg/dL suggest excess protein or poor synchronization (Figure 2). While not a standalone measure, tracking MUN trends can help fine-tune rations. A highly effective approach is to improve the balance of nutrients reaching the cow. By supplementing limiting amino acids such as methionine and lysine, nutritionists can reduce overall crude protein levels while still meeting the cow’s metabolizable protein requirements. Although rumen-protected amino acid products add cost, they can allow for reduced inclusion of expensive protein sources like soybean meal, often resulting in a favorable economic return when protein prices are elevated (NASEM, 2021).
The evidence is clear that well-balanced diets with moderate crude protein levels can sustain milk production while reducing nitrogen losses and feed costs. Achieving this requires attention to the balance between protein and energy, consistent forage quality, and the use of practical monitoring tools such as MUN. As feed prices remain volatile and environmental pressures increase, focusing on nitrogen efficiency offers a realistic and effective strategy for Northeast dairy farms. Improvements in ration formulation and feeding management can translate into meaningful gains in both profitability and sustainability.
— Isabela Carrari
