I recently spoke to a veterinarian who had tentatively diagnosed urea toxicity in a group of sheep. It reminded me of the importance of preventing these conditions by being aware of what is fed to cattle and sheep, especially with regard to protein supplements.
Protein is an essential component of rations for cattle and sheep. Most of it comes in the form of “natural protein,” but ruminant diets can occasionally contain a non-protein nitrogen source such as urea.
Many of our common feedstuffs naturally contain some level of non-protein nitrogen.
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Simple stomached animals, such as pigs and chickens, cannot make use of large concentrations of non-protein nitrogen in the way that ruminants can.
Urea is the most common non-protein nitrogen source added to cattle and sheep feed. Its goal is to supply nitrogen to the bacteria in the rumen.
Urea is broken down to ammonia in the rumen, and the ammonia, which contains nitrogen, is used by bacteria in the rumen to produce microbial protein. This microbial protein can serve as an additional protein source.
The rumen absorbs the ammonia that rumen microbes don’t use and converts it back to urea in the liver for excretion.
Ruminants are able to use non-protein nitrogen sources, which are often economical and can serve as a replacement for some of the animal’s protein requirements.
This process requires adequate energy sources in the rumen so that the bacteria can convert the ammonia into protein.
In most cases, including an energy source such as grain or molasses in the diet improves urea use.
Inadequate energy or feeding too much urea can allow large amounts of ammonia to enter the bloodstream and possibly exceed the liver’s capacity to remove it, which can result in toxicity.
The rumen can gradually adapt to higher levels of non-protein nitrogen, but that rumen adaptation is quickly lost if the cattle or sheep go without the non-protein nitrogen source for more than a day. Previous levels of non-protein nitrogen may then cause toxicity.
Clinical signs usually occur quickly after ingestion of the non-protein nitrogen source: within 30 minutes to four hours.
Animals will appear weak and have an increased respiratory rate. They may have tremors, excessive salivation and appear unco-ordinated.
They may eventually bloat and have severe muscular spasms before death.
Urea toxicity is difficult to treat because death occurs quickly.
A veterinarian can take blood samples from live animals for ammonia concentrations, which can help with the diagnosis.
Treatment focuses on lowering ammonia absorption from the rumen.
Two to six litres of vinegar are often used to lower the pH of the rumen to minimize ammonia absorption.
It is vitally important to closely read all feed tags and check for urea content in protein blocks, liquid supplements and range cubes.
Producers who are adding a supplement containing urea to a mixed feed should make sure that the ration is thoroughly mixed so that the urea is distributed evenly throughout the feed.
Urea cannot be top dressed on feed. It must be thoroughly mixed.
Non-protein nitrogen sources should be used only when a readily available energy source is available, such as good quality forage, grain or molasses.
However, it is important to note that the molasses contained in many liquid supplements will not be an adequate energy source when combined with low quality forages. As a rule of thumb, do not feed supplements containing urea to animals that are receiving only a low quality forage diet.
Calves less than 400 pounds and young lambs should not be fed urea.
Animals that are fed urea supplements should receive them daily. A continuous intake is necessary to keep the rumen microbes adapted.
Consult a veterinarian or a nutritionist to determine the appropriate level of urea to be fed to animals because the level will change, depending on the level of carbohydrate in the ration fed.
Non-protein nitrogen sources such as urea are often used as an economical ingredient, which can improve the crude protein levels of ruminant diets.
It is important for producers to know if any of the supplements they feed to their animals contain significant levels of non-protein nitrogen such as urea.
They can then manage this ingredient appropriately and ensure there are no significant toxicity issues.
