Protein and urea supplementation

Peter Smith
Formerly Department of Agriculture and Food

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The need for protein supplements

All grasses in northern Australia provide high quality grazing while they are actively growing but as they mature and seed their feed value declines. Grasses become more fibrous and difficult to digest as they mature with the result that the nutrients in the grass become less accessible to cattle.

In a grazing sense little can be done to improve the digestibility of mature grass but appropriate supplements can increase the rate at which digestion occurs. Faster digestion results in an increase in the amount of grass eaten, resulting in improved animal performance.

The rumen, or first stomach, is where a lot of the physical breakdown of the forage eaten by cattle occurs. Most of this feed breakdown is a result of activity by various types of microbes (bacteria and fungi) present in the rumen. Healthy populations of these microbes are largely dependant on adequate levels of nitrogen, sulphur and energy in the diet. These elements are key components of most protein sources.

During the pasture growing season the protein content of the pasture is more than adequate to maintain a healthy population of rumen microbes. As the pasture matures and the protein content of the diet that grazing animals can select declines the rumen microbe populations also decline.

As the dry season progresses and the protein content of pasture continues to decline rumen activity also declines, feed intake declines and animals eat less of poorer quality less digestible feed. Without intervention from an improvement in pasture quality from rain or appropriate supplementation this downward spiral of declining feed intake of poorer quality feed can eventually result in animal deaths.

Role of protein supplements

Supplying protein supplements to cattle provides a source of nitrogen and sulphur for the development of large populations of desirable rumen microbes.

Protein fed to ruminants can be divided into two broad categories:

  1. Rumen degraded protein (RDP) – Protein that is broken down in the rumen by the rumen microbes to form microbial protein. These microbes are subsequently flushed out of the rumen and are digested along with bypass protein lower down the digestive system.
  2. Undegraded dietary protein (UDP) or bypass protein – Protein that escapes breakdown in the rumen and is digested in the fourth stomach (abomasum) and small intestines similar to microbial protein.

Protein meals such as cottonseed meal, copra meal and canola meal are common sources of rumen degradable protein, bypass protein and energy. Unlike protein meals, urea contains no energy or bypass protein but when fed to ruminants in association with sulphur (S) can be utilised by rumen microbes to improve rumen function and supply a source of microbial protein. Urea is commonly referred to as non protein nitrogen (NPN).

Nitrogen (N) is a major component of protein and the protein content of feeds is determined by multiplying the nitrogen content of the feed by 6.25. For example, cottonseed meal with a nitrogen content of approximately 6% has a crude protein content of approximately 37% (i.e. 6 x 6.25). Urea with a nitrogen content of 46% has a crude protein equivalent of 287% (i.e. 46 x 6.25); almost eight times the protein content of cottonseed meal. For more information see Nutrient composition of feeds.

The high crude protein equivalent of urea is the reason it is commonly included in supplements fed to grazing cattle during the dry season in northern Australia. Historically, urea has been the most cost effective source of crude protein available for ruminants. As the nitrogen in urea is basically utilised by the rumen microbes it is of little use as a protein supplement to species without a rumen, e.g. horses.

The rate at which digestion occurs is governed, to a large extent, by the number and type of microbes present in the rumen at any time. A large healthy population of microbes results in faster digestion of feed and an increase in feed intake.

Urea and cattle

The aim of a urea supplementation program is to improve the rumen function and animal performance by supplying a small amount of urea and sulphur (N:S ratio of 10:1) to cattle on at least a daily basis during the dry season.

Effective urea supplementation can result in an increase in appetite of dry feed of 30–50%. This should be considered when determining stocking rates.

While there is lot of argument about the amount of urea that should be fed, experience suggests that a level of 50g a head a day for breeders and 30g a head a day for dry and growing cattle will result in improved rumen function of cattle, grazing mature grass pastures in northern Australia. Where the level of protein in pastures is very low (5% and lower) slightly higher amounts may be required (e.g. 70g), especially for lactating breeders. For more information see Assessing pasture diet quality (NIRS) and Nutrient requirements of beef cattle.

Effective urea supplementation

Effective urea supplementation usually results in a reduction in the rate of weight loss. It seldom results in increased weight gain.

The effectiveness and economics of any supplementation program depends on all cattle consuming the desired amount of supplement on a regular (daily) basis. The only practical method of determining how much urea and sulphur is required is to multiply the number of cattle to be supplemented by the desired level of supplement by a convenient time between feeds.

For example: 500 breeders x 50g (0.050kg) urea x 7 days = 175kg urea + 8.75kg sulphur

This example shows the amount of urea and sulphur required to supplement 500 breeders for one week. What this amount of urea and sulphur must be incorporated with to be safely and effectively fed to cattle is another issue.

Urea can and will kill cattle if it is consumed too quickly.

Unfortunately it is neither safe nor practical to feed urea and sulphur alone to cattle in dry supplement systems. A number of ingredients must be added to dry lick recipes to reduce the risk of urea toxicity while encouraging adequate supplement intakes by all animals within the group being fed.

Ingredients commonly used in dry mixes to regulate intake include: salt, protein meals, alternative nitrogen and sulphur sources, and small amounts of molasses. While protein meals may enhance the nutritional value of the supplement; salt and low levels of molasses and protein meals generally only affect palatability or taste.

Different tastes are attractive to cattle in different areas. Some cattle may readily eat salt, while others will not. Cattle on some bore water will not eat supplements containing salt at all while cattle on basalt country generally crave salt.

Types of urea supplements

1) Blocks

Blocks are very convenient to feed to cattle and are generally safe although the old saying of ‘whenever urea is fed to cattle, deaths can occur’ still applies.

The amount of blocks required should be calculated and a record of feeding maintained. Feeding too many blocks is excessively expensive while consumption of too few results in poor cattle performance. The weight of blocks of a given urea percentage can be calculated as follows:

Determine the amount of urea required (use the same method as for a dry lick), that is:

500 breeders x 0.050kg urea x 7 days = 175kg urea


Divide the urea requirement by the urea percentage in the block, that is:

175kg urea x 100
= 583kg of 30% urea blocks
Or 175kg urea x 100
= 875kg of 20% urea blocks


2) Loose mixes

The majority of urea and sulphur fed to cattle is fed in the loose mix form. Often, loose mixes are customised for individual properties and prepared by feed merchants. The composition of loose mixes can be altered during the feeding program to achieve target intakes. Providing cattle with access to urea at all times will result in much more efficient supplementation and better cattle performance.

Loose mix recipes to achieve target intakes of urea can be determined for individual areas and even paddocks. These recipes can be determined and mixed on-property or once determined can be custom mixed. Loose mixes are generally cheaper per unit of protein than blocks.

Examples of some dry season lick recipes for breeders are:

Ingredient With phosphorus (kg) Without phosphorus (kg)
Salt 75 75 50 100 100 75
Urea 50 50 50 50 50 50
Sulphur 2.5 0 2.5 2.5 0 2.5
Sulphate of ammonia 0 10 0 0 10 0
Kynofos®* 25 25 25 0 0 0
CSM** or copra meal 0 0 25 0 0 25

*Used as an example only. **CSM = cotton seed meal

Options for introducing urea-based dry loose licks

Most cattle deaths from urea feeding are associated with initial introduction of urea, intermittent feeding (supplement allowed to run out for too long), and water or saliva pooling in feeding troughs.

There are many different views and experiences on the best and safest way to introduce cattle to urea supplements. The most important issue is to ensure that any dietary cravings that cattle may have are satisfied with something that is not toxic before urea is introduced. In many areas cattle crave or at least readily eat salt. In these areas it is suggested that salt alone is fed for at least a week and intake and animal behaviour is observed. If intake is excessive (e.g. in excess of 200 grams/head/day) feed for another week or until salt intake drops to a more acceptable level). Salt intakes should be recorded and used in the formulation of the supplement recipe. Supplement intake is unlikely to increase with the addition of urea and particularly sulphate of ammonia (sulphur source) to the salt as both are relatively unpalatable to most cattle.

Once initial cravings are satisfied experience suggests that it is probably safer and more convenient to move to a full strength mix of say 20–30% urea than introduce urea gradually. Anecdotal evidence from many areas of north Queensland suggests that urea toxicity is more likely to occur with mixes in the 10–20% urea range than at higher levels. One explanation for this might be that the concentration of urea is insufficient to limit intake by its inherent bitterness.

Records of supplement fed, cattle numbers and average intakes should be maintained to ensure that the desired amount of urea and sulphur is being consumed. If intake is too low, cattle will not perform as well as they should. If intake is too high there is an increased risk of toxicity, cattle may not be utilising the additional urea and sulphur and it will be unnecessarily expensive. In both cases it may be necessary to alter the formulation of the supplement to correct the intake.

Producers with experience on how their cattle are likely to behave with supplements usually work out a system which works for them. It is therefore always a good idea to discuss management issues with other producers in the same area who have experience with supplementation and to learn from their experience.

Many producers have reported that the inclusion of low levels of cottonseed or copra meal in dry loose mix supplements has improved cattle performance. The intakes of protein meal achieved (around 50g a head a day) from common urea/sulphur loose mix supplements, will not provide a significant nutrient benefit to animals. The addition of protein meals usually increases the proportion of cattle in the mob which consume significant quantities of supplement, thus improving the overall performance of the mob being supplemented. Protein meals in dry urea mixes may also reduce the likelihood of poisoning by ‘soaking up’ moisture from saliva and small falls of rain.

All troughs used for feeding loose mix supplements containing urea should have clear drainage to avoid water pooling following falls of rain and in some climates from saliva and atmospheric moisture.

3) Water medication

The quality of water to be used must be checked and water reticulation systems designed to suit the equipment before installation. Medication units are expensive, $2,000–$3,000 installed, so consideration should be given to situations where one unit can supply several troughs; water quality permitting.

The attraction of water medication is that all cattle on medicated water will receive the supplement and as water intake is related to liveweight, target urea and sulphur intakes are more likely to be achieved for all individuals in the mob. This increases the effectiveness of the supplementation program.

4) M8U (molasses with 8% by weight of urea)

M8U has been widely used in many areas of Queensland to provide energy and protein to poor and weak drought-affected cattle and as a very effective supplement for weaners to ensure their continued growth.

M8U is considered to be a high energy, high intake supplement rather than a urea supplement. Breeders will commonly eat around 2kg of M8U a day.

A standard M8U mix is 1,000kg of molasses and 80kg of urea. M8U must be mechanically mixed until the urea is completely dissolved to reduce the risk of toxicity. For more information see Molasses supplementation.

Points to remember with M8U:

  • Mechanical mixing is essential for safety.
  • Mixing can be done in mixing trailers or truck mounted tanks where large quantities are to be mixed. Small quantities can be mixed with attachments to chainsaws or brush-cutters.
  • When mixing, put molasses in the mixer first then add the urea.
  • Do not mix the urea in water before mixing with molasses.
  • Mixing for at least 30 minutes should ensure that the urea is fully dissolved but check anyway. Undissolved urea can be felt like small grains of sand in the molasses mix. Use prilled urea (not granulated urea as used in dry licks).
  • Ensure that all safety guards are kept in place on mixing equipment as serious accidents have occurred.

5) Other feeding systems

Urea is included as a cheap nitrogen source in many other cattle feeds including feedlot rations. It is commonly used in high energy drought feeding rations as both a nitrogen source and a means of controlling intake by virtue of its bitter taste.

Urea supplementation in summary

  1. Urea can and will kill cattle if consumed too quickly.
  2. Urea must always be fed with sulphur at a ratio of 10N:1S.
  3. Identify and satisfy any depraved appetites or cravings cattle may have before including urea in a supplement.
  4. While horses cannot utilise urea like cattle they are less likely to suffer from urea toxicity than cattle.
  5. Hard dung is an indication of reduced rumen activity.
  6. Faecal NIRS will provide more accurate information for when supplementation is likely to be effective in reducing the rate of weight loss.
  7. Effective urea supplementation generally results in a reduction in the rate of weight loss; seldom weight gain.
  8. For best animal results supplementation should commence before animals lose too much weight.
  9. All loose mixed urea supplements should be fed in open ended troughs or troughs with good drainage.
  10. Determine target intakes of urea (e.g. 50g a day for breeders and 30g a day for growing cattle) and aim to achieve these intakes each and every day.
  11. Effective urea supplementation can increase animal feed intakes by up to 50%. Consider this when calculating stocking rates.
  12. Maintain records of supplement fed out and numbers and descriptions of cattle fed to ensure most effective use of supplement dollars.