UREA CAN BE A VALUABLE TOOL IN FEEDING PROGRAM

by: Stephen B. Blezinger
PhD, PAS

By this point I'm sure that everyone is aware of the fact that we are “experiencing” high, if not unprecedented, feed and grain costs. With these high prices comes a need by all producers to take steps to reduce this cost in any way they can and hopefully not compromise their performance too much. Feed companies and nutritionists in general are wearing out their formulation programs in an attempt to find that key ingredient or market “deal” that can save their customers money and make feeds and supplements at least a little more attractive. Saving money and finding a deal remains elusive.

One particular area that is very expensive is protein. Protein is one of our key nutrients and this year protein sources such as soybean meal, cottonseed meal, etc. have surpassed any previous highs. Many economists and grain traders believe there is a possibility that they may not come down in price as they typically do as we get into harvest. One reason being the shorter supply because of the drought in the Midwest but also because of economic conditions which are supporting the prices of these commodities. As these primary protein sources have increased in price, other proteins have likewise increased in sympathy.

One nutritional tool that has seen a significant amount of use over the years is urea. Urea can be used by the ruminant animal as a source of nitrogen with which the rumen bacteria can synthesize protein which the animal can digest and metabolize to meet its protein requirements. Over recent years urea has not been quite as attractive because of its cost. Since urea production is closely tied to the petroleum and natural gas production industries, its cost has increased along with other associated products. When prices of protein sources are lower urea, especially at higher prices, does not fit into many feed formulas because it is not cost effective. One reason for this is that urea is only a source of nitrogen and does not provide any other nutrients. But when grain and protein pricing conditions are high, urea begins to “price in” to a variety of formulas and helps reduce the cost of that product.

This article will review the background of urea use and examine its applications in current feeding programs.

The Big Question – Is Feeding Urea Safe?

Urea has been used for years in the feeding industry to provide an inexpensive source of nitrogen from which rumen bacteria can form protein. One thing that many cattlemen fail to understand is that much of the actual protein cattle digest and absorb comes from the bacteria which pass from the rumen and down into the lower digestive tract. Urea is a chemical that is used not only in livestock feeds but also as a source of nitrogen in some fertilizers. Like many materials found on the farm or ranch, especially those fed to cattle, urea consumption, especially excessive consumption, can create problems, including toxic effects. Most producers, if they have not experienced it themselves, have heard the horror stories of someone who have had cattle over-consume a urea containing feed and had cattle become sick or even die. Unfortunately, what many producers fail to realize is that in most cases, it wasn't the presence of urea in the feed that created the problem, but was mis-handling or mis-managing the feeding program or the cattle themselves. Often it will be found that the bad reputation urea has in certain areas is related to a poor experience by certain individual producers.

A statement needs to be made that in many situations, the feeding of urea or other generally considered safe ingredients is unjustifiably discouraged by a feed store, extension personnel, veterinarian or nutritionist simply because they have not done their homework or do not understand the ruminant digestive process, feed manufacturing technology or simple feeding management. As a producer, when you run across someone who makes a relatively strong statement (i.e., “feeding urea is bad for your cattle”) regarding a given feeding or management practice it is generally a good idea to check some other sources before implementing their advice. It has been said before that the feeding industry contains a tremendous amount of bad or inaccurate information. Virtually ANY feed component can cause problems if it is fed or managed incorrectly.

To truly understand urea feeding and urea toxicity, we need to discuss urea utilization a bit. Feed grade urea, at about 281 percent “crude protein,” is the most commonly used commercial source of non-protein nitrogen (NPN). The first question one typically asks is how can a product have 281 percent of anything? The 281 percent protein is more accurately termed “protein equivalent” and will vary depending on the source of the urea. In other words, one pound of urea can be used to make 2.81 lbs. of protein by rumen bacteria (one of the many beneficial functions rumen microbes perform). Enzymes from bacteria in the rumen, specifically urease, break down urea to carbon dioxide (CO2) and ammonia. Ruminal bacteria have the capacity to hydrolyze (break down) up to one gram of urea per liter (about a quart) per hour with diets high in urea. The ammonia which is liberated from urea is utilized in one of two ways. Part of the ammonia is ingested by the bacteria and is incorporated within the cell to form bacterial protein which is later digested by the animal as we discussed above. This bacterial protein accounts for a very significant portion of the protein actually absorbed and used by the animal to meet its protein requirements. The remaining ammonia is absorbed directly into the rumen wall where it enters the blood. From there it is carried to the liver where it is transformed back to urea. This newly reformed urea is then recycled back to the rumen through saliva or is excreted in the urine. Excretion is the predominant means by which excess blood ammonia levels are handled and eliminated.

For both the breakdown of urea and its incorporation into microbial protein, a readily available supply of energy is required. This energy is derived from the breakdown of other feedstuffs within the rumen. When feeding urea it is desirable to utilize a readily fermentable source of energy such as a processed grain or molasses. Urea can only be utilized with the energy present from readily available feed sources in the rumen. Specifically, the ruminal bacteria must have a source of carbohydrate (starch) with which to combine the nitrogen obtained from the breakdown of the urea molecule in order to form bacterial protein. Urea metabolism cannot utilize animal stores of energy such as fat tissue from within the animal itself. In formulation of feeds and rations it is important to recognize the usefulness of urea or NPN as well as the limitations.

A number of years ago Iowa State University outlined a system describing the urea fermentation potential (UFP) of feeds. This system provides an index which can be used to calculate the amount of urea which can be transformed into microbial protein per unit of feed consumed. For example, it was reported that the UFP of corn is 4.72 gms of urea per pound of corn. Likewise the UFP of cane molasses is 6.85 gms of urea per pound of molasses (45% higher). By weight, molasses can provide better and more rapid utilization of urea than corn. From this we can see that molasses based liquid supplements provide an excellent carrier for urea when used properly.

Cattle are adaptable to being fed urea. This simply means that given adequate time to adjust to urea feeding levels, the rumen bacteria can be adapted to higher rates. This needs to be done by gradually increasing the amount in the feed, allowing the bacteria which process the urea to adjust to the increased concentration.

Toxicity

Urea toxicity has been documented many times and is characterized by an over-consumption of urea containing feeds or feeding of urea without a suitable fermentable carbohydrate source. Primary causes include:

1) Poor mixing of feed

2) Errors in ration formulation

3) Inadequate period of adaptation

4) Low intake of water

5) Feeding of urea in conjunction with poor-quality roughages

6) Low feed intake prior to exposure to feed containing urea

7) Rations that promote a high pH in rumen fluid

In either situation, the breakdown of the urea and subsequent release of ammonia into the rumen exceeds the rumen microbe's ability to complex it into bacterial protein and thus the ammonia concentration in the rumen increases. This causes an increase in the rumen pH. This increase in the alkalinity of the rumen contents then facilitates the passage of the ammonia through the rumen wall. When this happens, excessive amounts of ammonia are absorbed into the blood stream. The increased alkalinity appears to be the most important factor contributing to high blood ammonia concentrations and related toxicity in animals consuming urea. This increase in blood ammonia concentration can exceed the liver's capability to process the ammonia back into urea for recycling in the salivary gland or the body's ability to excrete it through the urine. Concentrations of ammonia nitrogen approximating two to four milligrams (mg) per deciliter (dl) of blood are generally associated with urea-induced deaths. However, the chance of toxicity has been found to be high when blood ammonia nitrogen exceeds .8 mg/dl in 60 minutes following urea consumption. As in the rumen, when blood ammonia levels rise so does blood pH. This leads to interference in a number of normal physiological processes including normal cellular energy metabolism, increased uptake of ammonia by the brain and an upset of the central nervous system. Although not well defined, the precise cause of death in ammonia toxicity appears to be respiratory arrest. You will note that it is ammonia toxicity that creates the actual problem, not the urea itself.

Toxicity Symptoms

Clinical signs are usually apparent within approximately 20 to 30 minutes following consumption of a toxic amount of urea. Untreated, death may occur in less than 4 hours. As you can see, time is of the essence in these situations. Symptoms include rapid breathing, tremors, slight incoordination followed by severe incoordination, excessive salivation and labored breathing. Eventually, animals lose the ability to stand and tetany (muscle spasms) become increasingly apparent. Bloating tends to occur as rumen motility decreases.

Treatment

Fortunately, when caught in the stages early after ingestion, urea toxicity can be treated. Treatment focuses on reducing ruminal pH levels, overall concentrations of ruminal ammonia as well as urea breakdown. A 5% solution of acetic acid (common vinegar) can be orally drenched to aid in reducing ruminal pH. A dosage of about 1 gallon for a 1000 lb. cow will normally suffice if administered before tetany becomes severe. Also, additional quantities of cold water may be given orally to slow down urea hydrolysis (breakdown) and reduce the concentration already available for absorption. Once again, this is primarily effective only in the earlier stages.

Management

As with the other compounds we discussed, the best treatment is good management and prevention. By managing cattle and our feeding program carefully, feeding of urea inclusive products is a cost effective practice. Some of the management considerations to keep in mind include:

1) Never provide urea inclusive feeds to excessively hungry cattle where over-consumption might take place.

2) Adapt cattle to feeds containing urea slowly, over a period of one to two weeks if at all possible.

3) Do not “slug feed” feeds containing urea. In situations where cattle are only provided supplement once or twice per week (a practice I strongly discourage for a number of reasons), this feed should not contain urea.

3) Provide access to plenty of fresh water and good quality roughage.

4) Urea containing feeds should not contain urea levels which exceed 1/3 of the total protein content of the product. In other words, if a feed contains 20 percent protein, no more than 6.6 percent should come from non-protein nitrogen.

5) Make sure that feeds containing urea are well mixed and evenly distributed in the bunk.

Conclusions

Urea can be a valuable tool in the typical cattle feeding program and can be effectively used to help provide necessary nutrients as well as reduce costs as is necessary at this point in time. If common sense is used and good management practices are implemented, the potential risks involved in use of this ingredient become minimal. Remember, even “safe” ingredients can create problems if managed incorrectly. Taking the time to learn appropriate management steps and feeding practices will insure the safety of your program as well as increase producer overall profitability.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at sblez@verizon.net or at (903) 352-3475. For more information please visit us on at www.facebook/reveille livestock concepts.







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