Beyond Methane: Why Nitrogen Deserves More Attention in Dairy Sustainability

Refined nutrition strategies can help lower emissions and return energy to milk yield

Methane often steals the limelight in conversations about dairy sustainability, but nitrogen originating from excess crude protein and how it impacts the environment deserves just as much attention. When cows consume excess nitrogen, they excrete it in the form of urea in urine, which is then quickly converted to ammonia.

While ammonia itself is not classified as a greenhouse gas, it reacts with the environment to form nitrous oxide, which is a greenhouse gas. This means every bit of excess dietary nitrogen has both environmental and on-farm consequences, which makes managing it critical.

The impact of excess protein

Most discussions around nitrogen begin and end with manure handling. However, reducing nitrogen excretion before it reaches the manure pit can meaningfully impact a farm’s bottom line. When cows are fed more crude protein than they can use, or when their diet is poorly balanced for amino acids, the excess nitrogen must be converted into urea and excreted in urine. This process increases total nitrogen losses and costs the cow energy she could otherwise use for milk production.

This lost energy directly reduces efficiency and milk yield. Once excreted, that nitrogen also contributes to ammonia volatilization, nitrate leaching and nitrous oxide emissions, adding environmental and regulatory pressure.

By focusing on amino acid balance rather than simply raising crude protein in the diet, farmers can help improve feed efficiency, cut wasted nitrogen and support better environmental outcomes while maximizing milk production.

Reduce nitrogen output

Two strategies can help reduce nitrogen output from dairy cows: preventing overfeeding of crude protein and maximizing how efficiently cows use amino acids. Both are achievable with the nutrient technologies available today.

Excess crude protein, as well as protein that is unbalanced with respect to amino acids, are absorbed in the intestine and used by rumen microbes and the cow for energy, rather than supporting milk protein synthesis. Ammonia is created as a by-product of this process, which is

then converted to urea and removed from the bloodstream by the kidneys. This removal requires energy, and when there is excess nitrogen, the maintenance needs of the cow increase, impacting milk production.

Research conducted by the U.S. Dairy Forage Research Station shows that milk energy output was reduced, on average, by 60 kilocalories per gram of excess nitrogen excreted.¹ So, minimizing the nitrogen overage can result in improved milk yields by allowing more energy to be used for milk synthesis, rather than urea synthesis. This overage can be readily monitored by tracking milk urea nitrogen (MUN).

Improving amino acid balance also spares energy. When the diet’s amino acids more closely match what the cow requires, fewer amino acids are wasted as urea and milk protein yield is better supported.

Choose the ideal protein

The most ideal protein for dairy cows is microbial protein from the rumen. This protein has an amino acid balance that closely resembles the protein pattern needed to produce milk protein. A study done at South Dakota State University found that rumen microbial protein received the highest milk protein score, as illustrated in Table 1.² It is vital to maximize rumen microbial protein production.

Feed ingredients are then required to augment microbial protein and meet cows’ needs. While some ingredients are highly suited for this task, others are less helpful and should be used more sparingly. Unbalanced amino acids also contribute to lower milk protein.

Table 1: Milk protein score method to compare proteins (1.00 = perfect)³

		Limiting Amino Acid
Ingredient	Score	1st	2nd	3rd
Rumen microbial protein	0.78	Histidine	Leucine	Valine
Fish meal	0.75	Leucine	Tryptophan	Isoleucine
Canola meal	0.68	Isoleucine	Leucine	Lysine
Cottonseed meal	0.46	Methionine	Isoleucine	Lysine
Soybean meal	0.46	Methionine	Valine	Isoleucine
Sunflower meal	0.46	Lysine	Leucine	Methionine
Meat and bone meal	0.43	Tryptophan	Isoleucine	Methionine
Brewers’ grains	0.40	Lysine	Methionine	Histidine
Corn distillers’ grains	0.32	Lysine	Tryptophan	Methionine
Corn gluten meal	0.21	Lysine	Tryptophan	Isoleucine
Feather meal	0.19	Histidine	Methionine	Lysine

 

Nitrogen may not attract the same attention as methane, but its impact on both sustainability and productivity is significant. By preventing excess protein feeding and improving amino acid balance, dairies can reduce nitrogen losses, lower the energy burden on cows and support stronger milk production.

Microbial protein remains the gold standard for meeting amino acid needs, and feed ingredients like canola meal can help further support that balance. With the right nutritional approach, reducing nitrogen output becomes an opportunity to enhance both environmental stewardship and the bottom line.

References:

¹ Reed KF, Bonfá HC, Dijkstra J, et al. Estimating the energetic cost of feeding excess dietary nitrogen to dairy cows. J Dairy Sci 2017;100(9):7116–7126.

² Schingoethe DJ. Balancing the amino acid needs of the dairy cow. Anim Feed Sci and Tech 1996;60(3–4):153–160.

³ Canola Meal Feeding Guide. 2024. Canola Council of Canada