How do you make urea-treated rice straw, and how much does it help?

Urea-treated rice straw is ordinary rice straw soaked with urea fertiliser dissolved in water, then sealed for about three weeks. In that time the urea breaks down into ammonia, which raises the straw's protein and makes it easier for cattle to digest. The recipe used in research by Thailand's Department of Livestock Development (DLD) is 100 kg of dry straw, 5 kg of urea and 100 litres of water.

It doesn't turn straw into good grass. It makes straw you already have from the paddy a better feed than it was, which counts most in the dry season when fresh forage runs short.

UREA-TREATED RICE STRAW                                         
straw : urea : water = 100 : 5 : 100                            
                                                                
                                                                
                                   STEPS                        
  █                          █                                  
  █                          █   > 1 urea 5 kg in water 100 L   
  █                          █                                  
  █                          █     2 straw 100 kg, sprinkle     
  █                          █                                  
  █                          █     3 next layer, tread a bit    
  █                          █                                  
  █                          █     4 cover plastic, weigh it    
  █                          █                                  
  █                          █     5 seal about 21 days         
  ████████████████████████████                                  
         concrete pit              6 open, air before feeding   
                                                                

This post goes in the order you'd do the work: why treat straw at all, what to prepare, the steps, how to feed it, what it actually changes, and why urea itself is never fed directly.

Why is plain rice straw a poor feed?

Because it is low in protein and hard to digest. Feedipedia, the feed database run by INRAE, CIRAD, AFZ and FAO, describes rice straw as a source of energy that is low in protein (2-7%) and its high silica content results in a low digestibility. It has less lignin than other straws but more silica, and the leaves carry more silica than the stems.

Feedipedia's average figures are 4.2% crude protein in the dry matter and 49.8% organic matter digestibility in ruminants (Feedipedia). In the DLD trial this post leans on, the untreated straw measured only 2.37% crude protein (Sumamal et al., DLD Animal Nutrition Division research report 2007).

For good growth on a straw-based diet, Feedipedia gives 8 to 10% crude protein for young stock. Plain straw is a long way short.

How does urea change the straw?

Once urea solution is sprinkled on the straw, urease (an enzyme present in the straw) and bacteria on the straw's surface break the urea down into ammonia gas. A training handout from Suranaree University of Technology explains that the ammonia breaks down lignin in the straw, so the microbes in the rumen can digest it faster (SUT, urea-treated straw handout).

So treatment does two things. Nitrogen from the ammonia stays in the straw, which shows up as higher crude protein. And the cell walls become easier to digest, so the animal gets more energy out of the same amount of straw.

The urea is ordinary 46-0-0 fertiliser of the kind used on field crops (SUT). Sealing matters: ammonia that leaks out takes its nitrogen with it.

What do you need, and in what ratio?

The ratio in the DLD trial is dry straw : urea : water = 100 : 5 : 100 (Sumamal et al.).

The trial used a pit built from cement blocks, 6 x 6 metres, split into three bays of 2 x 6 metres, 120 cm deep (Sumamal et al.).

Without a pit you can treat straw in a heap on a plastic sheet. The SUT handout describes that method with 6 kg of urea and 100 L of water per 100 kg of straw, and warns that heaps lose urea solution and ammonia through leaks, and that once opened a heap should be used within 7 days before it spoils or goes mouldy. The handout says this is why the DLD's livestock breeding station in Chiang Mai recommended block pits for farmers who treat straw regularly.

The two sources differ on urea (5 kg against 6 kg). I've followed the DLD trial's 5 kg because it comes with measured feed values and animal results. If your district livestock officer recommends something else, go with that.

How do you make it, step by step?

These steps follow the method in the DLD trial (Sumamal et al.):

1. Dissolve the urea. Put about 100 L of water in a drum, add 5 kg of urea and stir until it has all dissolved.
2. Lay the first layer. Spread 100 kg of straw evenly across the pit.
3. Sprinkle. Use a watering can to pour all 100 L of urea solution evenly over the straw.
4. Repeat. Add the next layer of straw and sprinkle it the same way, until the pit is full. Tread the straw a little between layers, but don't pack it too tight.
5. Cover. Lay plastic over the top and tuck the edges down inside the pit walls so air can't escape.
6. Weigh it down. Put logs or other heavy things on the plastic to stop wind lifting it and to keep sun off.
7. Wait about 21 days, then open it.

For dry sugarcane tops instead of straw, the same report says to chop them short first so cattle eat them easily and less is spilled from the trough.

Checklist before you seal the pit

• Straw is dry and free of mould
• Urea and water weighed and measured for every layer, not guessed
• All urea dissolved, nothing left at the bottom of the drum
• Each layer wetted edge to edge, not only in the middle
• No holes in the plastic; edges tucked in on every side
• Leftover urea stored where cattle can't get to it

The last item is my own addition. The reason is in the section on urea poisoning below.

How do you feed it once the pit is open?

Air it first. The SUT handout says freshly opened straw has a strong ammonia smell that puts cattle off and stings the eyes, so leave it for 2 to 3 hours before feeding. Open the pit from one end only and keep the rest covered.

Feed it with some concentrate. The same handout says that when urea-treated straw is the main roughage, cattle need concentrate as an energy source so the rumen microbes can use the nitrogen to build protein, and clean water must always be available, because cattle short of water eat less straw.

In the DLD trial, cattle had as much treated straw as they would eat, plus a concentrate with 15.4% crude protein at 1% of body weight per day, fed twice a day, morning and evening (Sumamal et al.).

How much does it actually help?

In the DLD trial, crude protein went from 2.37% to 6.08% of dry matter after treatment, while NDF fibre barely changed (81.50% before, 80.36% after) (Sumamal et al., Table 1).

The animal results come from the same study, run at the Khon Kaen Animal Nutrition Research and Development Center from March to May 1996, with Red Sindhi bulls averaging 212 kg at the start. Five bulls ate treated straw for 84 days:

(Sumamal et al., Table 2)

Read those numbers carefully. The trial compared treated rice straw with treated sugarcane tops; it had no plain-straw group. The gain reflects treated straw plus concentrate, not treatment alone.

For a direct comparison with plain straw, Hart and Wanapat (1992) fed four swamp buffalo steers both diets in turn. On the urea-treated straw, organic matter digestibility rose by 17%, voluntary intake by 25%, and intake of digestible organic matter by 46% (Hart & Wanapat, Asian-Australasian Journal of Animal Sciences). Both diets were given enough nitrogen, minerals and trace elements, so the difference comes from the treatment.

Feedipedia's averages across studies point the same way: 7.9% crude protein and 59.9% organic matter digestibility for urea-treated straw, against 4.2% and 49.8% for untreated (Feedipedia).

What it doesn't fix

• Protein is still below what young stock need. 6.08% in the DLD trial is under the 8 to 10% Feedipedia gives for growing animals.
• It may add little on top of a protein supplement. Feedipedia notes one study in which urea treatment combined with protein supplementation did not give better results than supplementation alone.
• There are side effects. Feedipedia lists heavy urination and faster rumen washout as hazards of chemical straw treatments, urea included.

Why must cattle never be fed urea directly?

Because urea in the rumen turns into ammonia very quickly. When there is more than the microbes can use, ammonia floods the bloodstream faster than the liver can clear it, and South Dakota State University Extension says this may lead to urea poisoning in under 30 minutes. Common signs are uneasiness, tremors, excessive salivation, rapid breathing, incoordination, bloat and tetany.

The risk is higher when the diet is short of energy, which I'd say describes cattle living on straw in the dry season. The same guide advises:

• No urea in diets for calves under 400 lb (about 181 kg, my conversion) or 120 days old, because their rumen isn't fully working yet.
• No more than one-third of the diet's crude protein from urea.
• Never feed raw whole soybeans with urea, because they contain urease, which breaks urea down into ammonia fast.

Treating straw is different from feeding urea, because the urea is broken down to ammonia in the pit during treatment and the remaining smell drops while the straw airs. The real risk on a farm, I think, is an open fertiliser bag or a drum of leftover urea solution that cattle can reach. Keep both out of their way every time.

Sources

• Witthaya Sumamal, Taweesak Chuenpreecha, Phaiboon Phonbul: The use of urea treated sugarcane top as roughage for beef cattle in dry season, DLD Animal Nutrition Division research report 2007 (in Thai, English abstract)
• Suranaree University of Technology: Making urea-treated straw (training handout, in Thai)
• Heuzé V., Tran G. (2015): Rice straw, Feedipedia (INRAE, CIRAD, AFZ, FAO)
• Hart F.J., Wanapat M. (1992): Physiology of digestion of urea-treated rice straw in swamp buffalo, Asian-Australasian Journal of Animal Sciences, pp. 617-622
• South Dakota State University Extension: Considerations of Urea Use in Cattle Rations