Non-protein nitrogen (NPN) is often a controversial topic amongst producers. When used appropriately, NPN can be an exceptional source of rumen degradable nitrogen and reduce production cost. When used in the wrong scenarios, NPN will provide minimal benefit and just become an added cost. Let’s discuss the pros and cons of NPN supplementation and when it works best.
Proteins are composed of multiple amino acids arranged in proteins. In the ruminant animal, proteins and nitrogen are required by the rumen while amino acids are required by the animal. A protein is composed primarily of carbon, oxygen and nitrogen. On average, nitrogen makes up 16 percent by mass of proteins.
On a forage based diet, it is critical to provide the nutrients necessary to maximize nutrients extracted from forage in the rumen. In fact, a good nutrition program for the rumen bacterial population can allow ruminants to extract more nutrients from their forage base and more efficiently utilize their forage resources. Cattle and other ruminant animals have the ability to convert NPN like urea into proteins that can be utilized by the animal. Bacteria in the rumen are capable of taking a pure nitrogen source like ammonia (NPN) and carbon (energy) and synthesizing amino acids which are available to the animal. Even without feeding a source of NPN like urea, degradable fractions of natural proteins will be broken down into ammonia in the rumen. Also, a portion of measured protein in many forages is actually NPN. The rumen requires NPN for bacterial function and degradation of carbohydrates. The challenge with NPN in forage diets is the ability to provide nitrogen at the rate it is utilized by the bacteria. Most forms of NPN available for cattle diets are rapidly available in the rumen while forage degradation is slow. Natural proteins in general are slower to degrade in the rumen so they provide a more constant source of nitrogen for the rumen bacteria.
Unlike monogastric species, ruminants also have the ability to recycle excess nitrogen for days after it is fed to provide a source of NPN to rumen bacteria. On the other hand, excess nitrogen in the diet that cannot be used by rumen bacteria or recycled has to be scrubbed by the liver and excreted in the urine which comes at an energetic cost. In most situations when protein is required in the diet, it is most economical to use a source of natural protein and NPN to fulfill the rumen’s requirement.
The Cost Advantage
NPN has a significant cost advantage when compared to traditional natural protein sources used in feed, but it comes at the expense of containing no energy. Unlike most natural protein supplements that provide rumen degradable nitrogen, amino acids and energy, NPN supplies strictly rumen degradable nitrogen. If you price common feed ingredients on a dollar per unit of nitrogen basis you will find that products like urea have potential to lower the cost of a protein supplementation program.
When compared to traditional protein sources, NPN can provide a significant decrease in feed cost and improve cost of gain, but it needs to be used correctly in order to do so.
The Right Situation
There are several good fits for the use of NPN, but most importantly energy content and degradability needs to match nitrogen available in the rumen. Rumen bacteria use sources of energy and nitrogen simultaneously to manufacture microbial protein. The optimum use of NPN is actually in high energy diets because the rapidly available nitrogen source matches the degradation of readily available carbohydrates in the rumen. Another way to think about it would be when readily degradable carbohydrates are available like starch or sugar, the microbial population needs nitrogen available to utilize these carbohydrates. This is why when energy concentration in the diet goes up, protein requirements also increase because the bacteria need more nitrogen to utilize more energy. A general rule of thumb is to maintain degradable intake protein at a ratio of 7 or less to TDN content of the diet. In the table to the right, you will see a chart of different feed ingredients and their ability to utilize NPN in a supplement.
The best situations for NPN are when energy in the diet is adequate but protein needs are not met. For example, when forage is high in energy (>60 TDN) but low in protein (<8 percent) like many warm season grasses, NPN would be a good option to meet nitrogen needs in the rumen. Another situation where NPN works well is when supplemental energy is needed, corn along with NPN could be provided to optimize utilization of the corn and forage base in the animal. Lastly, NPN also works well when used alongside a protein source that is not very degradable in the rumen like DDGS.
NPN sources like urea work best at lower levels. A general rule of thumb would be to never provide more than 1/3 of the protein in the diet from NPN. I would go a step further and say that never provide more than 15 percent of the protein supplied on forage based diets from NPN.
The Wrong Situation
Utilizing NPN to exceed protein requirements in the animal will provide no benefit. For example, in a vegetative cool season grass, protein content can measure 16 to 20 percent on a dry basis. In this situation, energy, not protein, would be limiting bacterial fermentation potential and supplying additional NPN in the diet would simply cost the animal more energy to dispose of nitrogen. Additional situations where NPN should be avoided would be when horses or other monogastric species are consuming the same feeds. Also, calves without a fully developed rumen should not be provided feeds with NPN.
Rules Of Thumb
Just like ionophores, NPN can be a great tool to reduce production cost, but it needs to be used precisely in every feeding situation. I have included bullet points below to highlight the do’s and don’ts of NPN supplementation.
- Lower feeding levels of NPN are more efficiently utilized than higher feeding levels.
- High levels of NPN ( >0.20 lbs urea/head/day) can be toxic to cattle.
- NPN requires energy to work efficiently (works well when energy is supplemented).
- Monogastric species and young calves cannot utilize NPN and should not be exposed.
- NPN supplementation is more efficient with multiple meals per day so it is best supplemented in a tub, limited ration or TMR.