Urea supplementation

The need to supplement

The nutritional value of all grasses in northern Australia declines following the growing season. While some grasses are more attractive to cattle (palatable) than others, all grasses provide high quality grazing while they are actively growing.

As grasses mature and seed their feed value declines. The nutrients in the grass also become less accessible to cattle as grasses become harder to digest as they mature. As a result of this decline in pasture quality and digestibility cattle lose weight at an increasing rate as the dry season progresses.

In a grazing sense little can be done to improve the digestibility of mature grass but supplements can increase the rate at which digestion does occur. Faster digestion results in an increase in the amount of grass eaten. An analogy is the marketing strategy of low margin high turnover. In this case low digestibility higher intake results in improved animal performance.

Nitrogen to Sulfur ratio

For cattle the optimum ratio of nitrogen to sulfurin in the diet is about 13:1. This is about the same ratio as found in leaf protein, and as the pasture declines, the ratio remains constant. Hence, when supplementation with urea N commences, it would be beneficial to include a sulfur source. Without it, the utilisation of the urea and the dry feed may be reduced and a sulfur deficiency may occur.

Two grades of sulphate of ammonia are available from Incitec fertilisers of which only one (Incitec GranAm) is recommended for use as a stock feed supplement. GranAm, however, does contain granulation and coating agents that may cause a sediment to form in mixing tanks, particularly if the water is alkaline or hard, or if LiquifertP is used in the mix as well. (If this sediment becomes a problem, it may be necessary to purchase a higher-grade ammonium sulphate from another supplier.

Where GranAm is used as the sulfur source, add 1 par of GranAm to every 6 parts of urea, by weight.

How does urea work

The rumen or first stomach is like a large fermentation vat where a lot of the physical breakdown of fibrous material occurs. Most of this feed breakdown is a result of activity by various types of bacteria and fungi (rumen microflora) present in the rumen.

The rate at which digestion occurs is governed, to a large extent, by the number and type of microflora present in the rumen at any time. A large healthy population of microflora results in faster (but not more complete) digestion of feed and an added source of protein (microbial protein) for the animal. As the rumen microflora pass out of the rumen they are digested providing a valuable source of protein for the animal.

An unhealthy low population of rumen microflora results in slow digestion and a slow passage of feed. A reasonably reliable sign of poor rumen activity is hard dung.

Urea supplementation, in combination with sulfur, will enhance rumen activity by providing a nitrogen (N) and sulfur (S) source for the development of large populations of desirable rumen microflora. Large increases in numbers of microflora results in faster digestion of dry grass and faster throughput (rate of passage), of feed. This means cattle will eat more dry grass.

The urea and S, supplied as a supplement, is used by the rumen microflora and has no direct 'feed' benefit to the animal.

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

Urea and cattle

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

The aim of a urea supplementation program is to improve the rumen function and animal performance by supplying a small amount of urea and sulfur (N:S ratio of 13:1) to cattle on at least a daily basis during the dry season.

While there is lot of argument about the amount of urea that should be fed, experience suggests that a level of 60 g a head a day for breeders and 30 g a head a day for dry and growing cattle will result in improved rumen function of cattle, grazing mature grass pastures.

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 at the right rate. The only practical method of determining how much urea and S is required is to multiply the number of cattle to be supplemented by the desired level of supplement by a convenient time between feeds.

Example: 500 breeders x 60 g (0.060 kg) urea x 7 days = 210 kg urea + 30 kg GranAm

(Urea contains 46%N and GranAm contains 24%S)

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

The cheapest way to feed urea and sulfur to cattle would be to feed just urea and sulfur. Unfortunately this is neither safe nor practical with dry supplement systems. A number of ingredients must be added to urea and sulfur in dry lick recipes to regulate animal intakes.

While supplement intakes by individuals within any mob of cattle is likely to vary a lot; the aim is to reduce the risk of urea toxicity while encouraging adequate supplement intakes by all animals within the group being fed.

This is achieved by altering the taste of the supplement mix by including one or more ingredients in the supplement recipe. Ingredients commonly used in dry mixes to regulate intake include; salt, vegetable protein meals, small amounts of molasses and in some cases phosphorus sources. Vegetable protein meals and sometimes phosphorus may enhance the nutritional value of the supplement while the salt and low levels of molasses only affect palatability or taste.

Different tastes are attractive to cattle in different areas. Some cattle may readily eat salt, which 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 supplements


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 using the same method as for dry lick, i.e. 500 cattle x 0.060 kg urea x 7 days = 210 kg urea
  • Divide the urea requirement by the urea percentage in the block, i.e. 210 kg urea x 100 / 30 = 700 kg of 30% urea blocks or 210 kg urea x 100 / 20 = 1050 kg of 20% urea blocks.

Loose mixes

The majority of urea and suphur 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 than a "boom ´n´ bust" system of allowing cattle to run out for a period.

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:
IngredientWith phosphorus kgsWithout phosphorus kgs
Salt 75 75 50 100 100 75
Urea 50 50 50 50 50 50
Sulfur 2.5   2.5 2.5   2.5
GranAm   7    7  
Kynofos or Windmill DCP 25 25 25    
CSM*    25    25

*CSM = Cotton Seed Meal

It may be necessary to pour a small amount of molasses on top of the mixture in areas where cattle do not eat salt readily. For safety, this supplement should be protected from the weather.

Many producers have reported that the inclusion of cottonseed or copra meal in dry licks has improved cattle performance. Vegetable protein meals in dry urea mixes may also reduce the likelihood of poisoning by 'soaking up' moisture from saliva and small falls of rain. The addition of vegetable protein meals usually increases the proportion of cattle in the mob, which consume significant quantities of supplement.

Water medication

This method of supplementation is slowly becoming more widely adopted. The history of supplying urea to cattle via their drinking water documents a number of problems. Cattle deaths have occurred, usually due to equipment failure, and water quality has resulted in some problems.

The reliability of equipment currently available has improved and provided installed correctly should provide good results.

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 ($2000 - $3000 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. This increases the effectiveness of the supplementation program.

Roller drum urea/molasses mixes

Although largely superseded by the loose lick method of feeding, the roller drum system is probably one of the safest methods of feeding urea to cattle.

The main reasons the roller drum system declined from favour include:

  • the volume of water, molasses, urea mix required to be mixed and carted around properties
  • difficulty in controlling intake
  • capital cost and maintenance of roller drum feeders.

To avoid too rapid consumption of the mix, regulation of intakes can be controlled to some extent by increasing the water or decreasing the molasses concentration.

A roller drum mix to feed approximately 50 g of urea and 225 g molasses to 400 head for one week is:

  • 450 / (100 gal) molasses
  • *900 / (200 gal) water
  • 150kg (3 bags) urea

* the water can be increased to any level to slow intake.

The first mix fed can be fed with no urea or at most only 1 bag (50 kg). The mix can be increased to full strength over 3 feeds, i.e. 1, 2 and 3 x 50 kg bags of urea. Mixing is usually carried out in an open tank using a water pump to recirculate the mixture. The usual mixing order is to mix the water and molasses first and add the urea last.

Cattle should consume around 0.5 L of the above urea supplement mix a day. Three 400 L (90 gal) double drum lick feeders would be required to feed 400 cattle if troughs are only filled once a week.

5 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. It is also an 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 2 kg M8U a day.

A standard M8U mix is 450 L of molasses and 50 kg of urea. M8U must be mechanically mixed until the urea is completely dissolved to reduce the risk of toxicity. Each 450 L of M8U will feed about 2 kg a day to 50 head for a week.

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.
  • Ensure that all safety guards are kept in place on mixing equipment as serious accidents have occurred.

Other feeding systems

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

Urea supplementation in summary

  • urea can and will kill cattle if consumed too quickly
  • urea must always be fed with sulfur at a ratio of 13N:1S
  • identify and satisfy any depraved appetites cattle may have before including urea in a supplement
  • while horses cannot utilise urea like cattle they are less likely to suffer from urea toxicity than cattle
  • hard dung is an indication of reduced rumen activity
  • a response to urea supplementation is likely to occur when faecal protein falls below 8% (1.3%N)
  • effective urea supplementation generally results in a reduction in the rate of weight loss; seldom weight gain
  • for best animal results supplementation should commence before animals lose too much weight
  • all loose mixed urea supplements should be fed in open ended troughs or troughs with good drainage
  • determine target intakes of urea (60 g a day for breeders and 30 g a day for growing cattle) and aim to achieve these intakes every day
  • effective urea supplementation can increase animal feed intakes by up to 50%. Consider this when calculating stocking rates.