Improving the feed value of straw for sheep and cattle
Article printed May 29, 2025. For the latest version, please go to: https://www.feedinglivestock.vic.gov.au/2025/05/27/improving-the-feed-value-of-straw-for-sheep-and-cattle/
Background
Straw is generally a poor quality feed for ruminants. Ruminants depend on micro-organisms (bacteria, fungi and protozoa) in the rumen to breakdown the fibre in the straw. The main limitation of straw is it’s low and slow digestibility. This poor digestibility is caused by a series of factors:
- fibre cannot be digested easily;
- the efficient functioning of rumen micro-organisms is limited due to straw’s:
- low protein content
- lack of easily available energy
- low content of essential minerals
Therefore, poor digestibility and a low rate of digestion result in low straw intake. This problem can be overcome by:
- chemical treatment of straw;
- stimulation of rumen function by adding protein and/or soluble carbohydrates;
- addition of nutrients, such as protein, to provide readily available energy and minerals which are deficient in the straw.
Urea treatment of straw is able to meet many of these objectives, including an increased intake.
Rumen Micro-organisms and their work
Rumen micro-organisms will not work ‘free of charge’. They also need ‘food nutrients’ in a simple form to keep them growing and multiplying. Unfortunately straw does not contain enough of these ‘food nutrients’ to allow the rumen micro-organisms to work efficiently and help the host ruminant in return. As the micro-organisms grow they produce enzymes, which digest the fibre. One such enzyme is Cellulase, which digests cellulose, the main constituent of fibre in straw. Urea is a nitrogen compound that can be used in ruminant feeding. The micro-organisms in the rumen transform urea into protein. Feeding urea to ruminants is useful especially when the feeds available are low in protein, e.g., straw and other poor quality roughage’s. Under certain circumstances urea can be poisonous. If proper care is taken the advantages of urea can be extensive.
How to Treat the Straw
Treated straw is obtained by the addition of 5% Weight/Weight (w/w) of urea plus 80 to 85% w/w water. So, to treat 1 tonne of straw, 50 kg of urea fertiliser needs to be dissolved in approximately 800-850 litres of water. This solution should be sprayed onto straw. If you do not want to break the straw bale, work out the weight of the bale so that the correct amount of solution is applied. For example, a big square bale weighing 400 kg needs 20 kg of urea dissolved in 320-340 litres of water and the resulting solution sprayed/soaked onto it.
After spraying the urea solution, it is critical that the straw is contained in a reasonably airtight condition (e.g. covered in plastic or old bunker tarp) for a period of time to facilitate the chemical reaction/treatment process. You should keep the straw covered for 7-10 days in summer months 2-3 weeks in winter after treatment. After the treatment period is over, the plastic can be removed and the straw can be fed to livestock ad lib in a hay rack or on feed pad. Treated straw can be preserved without reduction in feed value for more than a year, provided it is protected from the rain damage.
For those that are chemically minded, the reaction that takes place during the straw treatment process is presented below:
Feeding of urea treated straw
Like any other new feed, animals will take 2-3 days (a week maximum) to adjust to treated straw. It may be useful to aerate (to allow the excess ammonia to dissipate) the straw during the first few days of adaptation. Once their rumen is adapted there are no advantages in aeration over fresh feeding. The treated straw can be fed ad-lib in a hay-rack or in a feedpad. The treated straw can be preserved for a long period (more than a year) provided it is protected from rain damage. The primary objective of feeding treated straw is to improve its utilisation and protein content. The improvement in protein could be up to 3 to 4 times depending upon the untreated straw quality. Research all over Europe and Asia has proven that the level of costly supplementation necessary for animal production is much less with treated straw. FEEDTEST® results of 1 treated wheat straw found the protein level compared to untreated straw increased from 2.1% to 14.7%. A slight improvement in digestibility (%) and Metabolisable Energy content (MegaJoules/kg of Dry Matter) of straw was also noted.
| WHEAT STRAW | |||
| Test | Unit | Before treatment | After treatment |
| Moisture | % | 9.5 | 49.2 |
| Dry Matter (DM) | % | 90.5 | 50.8 |
| Crude Protein | % of DM | 2.1 | 14.7 (↑7 x) |
| Neutral Detergent Fibre | % of DM | 69.7 | 78.2 |
| Digestibility | % digestible DM | 46.7 | 48.0 (↑2.8%) |
| Metabolisable Energy | MJ/kg DM | 6.4 | 6.7 (↑4.7%) |
Answers to some of the common questions asked about urea treated straw feeding
Summary & Acknowledgement
The authors of a book titled “Feeding of urea-ammonia treated rice straw’ has compiled some questions which are often received from farmers, extension workers, students and other workers in similar fields. Therefore, the answers are very practical, figures are approximations, more to be taken as indications rather than as answers that have specific validity in all situations.
How to feed straw?
Q1. Why feed treated straw instead of untreated straw?
A. It does not always make sense to feed treated straw even though it is better quality than untreated straw. Economics will determine which of the two types of straw should be fed. Moreover, if there is sufficient pasture is available, there is no need to feed straw at all.
Q2. Why is treated straw better than untreated straw?
- There are so few nutrients in untreated straw that an animal would have to eat more straw than possible in order to satisfy its demand for energy, protein, minerals and vitamins. The problem of limited intake (consumption) is especially serious when the animal is producing meat, milk or is pregnant. This is because the animal needs increased amounts of nutrients (energy, protein, minerals and vitamins) at increased levels of production. The quality as well as the intake of treated straw is better than that of untreated straw.
Q3. Whys is untreated straw such a bad feed?
A. Straw consists of mainly indigestible fibres. Try dissolving straw in a glass of water compared with a cube of sugar. Both sugar and fibre have basically the same chemical structure, but fibre needs special enzymes to dissolve it. The fibre also contains lignin, which binds it together. Lignin itself is indigestible to ruminant. The low protein content and the deficiency of minerals, make optimum rumen function difficult.
Q4. Is straw treatment the only alternative?
A. If not enough nutrients can be obtained from the untreated straw, it is possible to supplement the deficiency by adding cereal or legume grains (or screenings) or good quality hay. When these supplements are expensive and straw is cheap it will be profitable to improve the straw quality itself rather than to use expensive grain or hay.
Q5. What is the value of untreated straw alone?
A. Untreated straw may be not enough for the animal to keep itself alive (maintenance) when little supplement is provided.
Q6. What is the main difference between urea-supplemented straw and urea-treated straw?
A. The main difference is that in the case of urea-treated straw, the urea is allowed to react with the straw for some time (e.g. 7-10 days, pre-digestion). This increases the feed value and intake of straw by ruminant. If the straw is only sprayed with urea and fed directly, there is only small advantage of added
urea that stimulates rumen function and serves as protein. No pre-digestion takes place and intake is not improved as much (10% on Urea-supplemented Straw vs 30-40% on urea-treated straw).
Q7. If there is plenty of grass, should treated straw be fed?
A There is no need to feed treated straw if there is enough other good quality roughage (hay) available.
Q8. Do animals refuse to eat treated straw because of smell?
A. Long practices have shown that in spite of the ammonia smell, cattle and sheep will eat treated straw well. There is no need to aerate the straw. However, the animals may have to get used to the smell. This may take a few days, so do not give up.
Q9. Can any additional green pasture be fed if treated straw is fed?
- Most certainly, it is even advisable to include a small amount of green feed for a supply of minerals and vitamin A.
Q10. Can all types of straw be treated?
A. All straw can be treated but do not waste time and money on mouldy, very old straw. Otherwise an inferior and unpalatable end product will be obtained. The straw of non-cereal crops is less likely to improve much with treatment and better quality straw is also less likely to improve with treatment.
Q11. What are the main reasons of failure of the treatment process?
Straw treatment is probably less difficult and sensitive than making a good grass silage. Chances of failure are not great but a few causes can be mentioned. The use of straw that is too wet and green will yield an inferior and unpalatable product. If the ammonia escapes too rapidly there is a greater chance of mould formation; longer treatment times will also increase the incidence of mould.
Q12. Is there a difference between silage making and straw treatment?
- These two processes are completely different. Silage making is microbiological fermentation process for preserving grass, whereas straw treatment is done with a chemical and is not intended as a storage method.
| Grass Ensiling | Straw Treatment | |
| Basic process | Microbial fermentation | Chemical reaction |
| pH during process | Acid (decreases) | Alkaline (increases) |
| Addition of urea | Not essential | Essential |
| Purpose of the process | Conserve feed value | Increase feed value |
| Effect on nutritive quality | Negative | Positive |
| Need for airtightness | Essential | Desirable |
| Cost of ‘structure’ | More expensive | Less expensive |
| Purpose of sealing | To keep air out | To keep ammonia in |
What are the health aspects of feeding urea treated straw?
Q13. Is urea toxic?
- Urea in the treated straw is not toxic. Urea is toxic if you allow animals to drink the urea solution or the animals have a mouthful of urea granules. Apart from this, no special precautions are needed. Feeding urea on straw is much less risky than feeding a large amount of urea mixed in grain ration or pellets. Safety recommendations which apply to urea feeding on mixed ration/pellets/liquid & solid lick blocks are not applicable and are probably less critical on straw diet. Good mixing is almost always guaranteed with straw because the urea solution is sprayed onto it, excluding the possibility of finding lumps of urea. Moreover, the intake of straw and adhered urea protein with it is necessarily much slower than that of mixed grains and pellets. Fertilizer grade urea is also safe for people to handle but it should be neither eaten nor drunk. Urea is a compound that occurs naturally in the rumen, blood, saliva and urine of ruminants.
Q14. Is the ammonia smell toxic to human?
- Too much alcohol is also toxic. Discomfort is avoided by keeping away from the strong ammonia smell.
Q15. Does feeding of treated straw affect fertility?
- It is highly unlikely. Poor nutrition affects fertility far more than treated straw feeding. Feeding minerals is, nevertheless, just as important with straw feeding as it is with grazing. Vitamin A needs special attention.
Straw treatment techniques
Q16. How much urea and water should be used when treating straw?
- For example, to treat 1000 kg of straw: dissolve 50 kg of urea in a maximum of 800 to 850 litres of water. Pour, hose or spray the solution on top of the straw bale. Make sure you know the approximate weight of the straw bale and approximate capacity (litres) of the container in which you dissolve the urea. Use a pressure hose for faster dissolving of urea.
Q17. For how long should the straw be treated?
- A treatment period of 7 to 10 days is enough. In typical Mallee climate 7-10 days during summer months and 14 to 21 days during winter is enough. In colder areas the breakdown of urea (into ammonia gas) takes more time. Straw can be kept under plastic even a few weeks after the recommended treatment period is over. But it is advised to start feeding to animals or stored in a hay shed once the treatment period is over.
Q18. What happens when the straw is treated for a longer period?
A. Basically nothing happens. It can be even advantageous in some system to treat all the straw at once. It may be useful for those farmers who traditionally stack all their straw right after harvest, to treat it while stacking. If you are not going to use all the straw in one season than dry storage is better than storage in the treated form.
Q19. Can treated straw be fed to calves?
- Treated straw should not be fed until calves are well adapted to eating grass and hay. This means that the rumen has to be well functioning.
Q20. Why straw need to be covered during treatment and what kind of covering should be used?
A. During the treatment period straw need to covered to keep the ammonia has as much as possible inside. The best material is black polythene. Old tarp from grain silo also does a good job.
Acknowledgement of Information Source:
Schiere J.B. and Ibrahim M.N.M. (1989) Feeding of urea-ammonia treated rice straw: a compilation of miscellaneous reports produced by The Straw Utilization Project (Sri Lanka), Pudoc, Wageningen, The Netherlands.
This article has been reproduced from previously published field day notes prepared by Shyamal Das in 2002
