Nitrogen use in dairy cows

Nitrogen (N) is the building block for proteins found in feed and fodder. Protein is usually the most expensive component used in purchased feed for dairy cattle rations.

Nitrogen has drawn attention as a significant component of nutritional management plans on dairy farms as well as due to concerns regarding ammonia emissions.

Understanding how N is used in dairy cattle is important for improving profitability while also reducing nitrogen excretion into the environment.

It is worth recalling that dairy cows do not require protein per se. What they actually need are available amino acids within the small intestine for their uptake and use to support tissue growth and milk production.

N use in dairy cattle basically consists of two elements:

• The first of these is to provide an adequate supply of N and carbohydrates to support the growth of rumen microorganisms and the production of microbial crude protein (MCP).
• The second part of this system involves the use of amino acids found in the small intestine to meet the cow’s nutritional requirements.

Nitrogen fractions in feed

Although all foods contain N, the amounts in which it found in different feeds, its availability and how it is used by dairy cows can be highly variable. Forage analysis laboratories determine the amount of N in analyzed samples and multiply this value by 6.25 to obtain the crude protein (CP) value.

Although different feeds may have the same CP value, the nutritional value for the dairy cow will be different depending on the feed. Let’s look at the following examples:

• Alfalfa hay, alfalfa silage and alfalfa grass – All have 20% CP.
• Raw and roasted soybeans – Both with 40% CP