Unlocking the nutrient potential of low quality fodder with Urea treatment
Introduction:
The original work on treatment of crop residues was done in Northern Europe. The preservation of straw (with ammonia), which was damp at the time, was the main reason for the investigation and the improvement of quality was incidental. The possibilities of this became apparent as the technology developed. The treatment of low quality fodder with ammonia (as gas, liquid ammonium hydroxide or urea-solution) is widely used in the large grain producing areas of America and Canada. Uptake of this technology has been slower than expected in Africa but slightly better in China and India. The main reasons sited for the slow uptake in third world countries was:
Cost and availability of urea
Cost and availability of sealing materials
Labour constraints for gathering straw (by hand) compared to grazing
Seasonal variation in feed supply
Benefits are not always obvious to poor farmers
Transport costs of residues
Lack of knowledge and training
Rigid procedures for applying treatment (especially with ammonia gas )
None of these constraints should apply to farmers. With our level of mechanization in the agricultural industry, this “new” technology could easily be adopted. There are three sources of ammonia that can be used in treating fodder. Using the urea treatment was decided on as it is safe, easy to handle, readily available and has none of the constraints of the other two ammonia sources.
At best rank grass-hay can barely sustain maintenance requirements for dry stock and at worst cereal straw is only good enough for “bedding” material. These low quality fodders can however be treated on-farm with no extra capital expense and at very little added costs to become useful fodder.
After treatment with urea, straw can be turned into feed capable of sustaining body weight through winter. Low quality grass will provide the nutritional requirements of lactating sheep and beef cattle after treatment.
Inclusion into rations for high producing dairy cattle should be limited though.
Urea is mixed with water and sprayed onto hay, just prior to wrapping, or injected into hay bales after wrapping and resealed.
What can be achieved?
Urea-treatment (ammoniation) can increase crude protein (CP) content of wheat straw from (4% - 6%) to (12% - 14%) and mature grass hay from (8% - 12%) to (18% - 20%).
Digestibility of straws can be improved by 5% to 10% and 10% to 20% for mature grass hay and maize stover. Voluntary intake of low quality forage can also be increased substantially and combined with the higher digestibility a significant increase in the total energy intake per animal can be achieved. An added advantage of urea-treatment is the effective preservation of hay and silage with up to 30% moisture.
How does it work?
Urea (NO2)2CO is made by combining ammonia (NH3) with carbon dioxide (CO2).
When urea is mixed with water the ammonia is released again. The rate of release is determined by temperature and the treatment duration will vary from 3 weeks in summer to 7 weeks in winter. In an airtight environment, like a wrapped hay bale or tube, the ammonia released from the urea–solution will attach itself to the hay fibers. Urea-treatment can be done in 24 hours by packing hay bales, treated with urea-solution, into a large airtight container and heating it to 90 degrees C.
Increasing Crude Protein content:
Nitrogen makes up 78 percent of air but is unavailable to most living organisms. In nature there are two ways it can be made available to plants. The first is by lightning and the second is through the bacterial action on the roots of legumes, and in the rumens of ruminants.
The bacteria in the rumen build the nitrogen into their own bodies to form microbial protein. The bacteria move, with the broken down feed, through the four stomachs and in the last stomach it gets killed by the gastric juices (hydrochloric acid) that is secreted there. Microbial protein is then digested and absorbed the same way as any other protein in the animal’s diet.
By increasing the nitrogen available to the rumen bacteria more microbial protein can be produced and made available to the animal.
In monogastric grazing animals, like horses, bacteria live in the blind gut or ceacum. Microbial protein is not available to the animal as the ceacum is too far down the digestive tract for protein to be digested and absorbed. Hay treated with urea should therefore not be fed to horses and could even cause urea poisoning.
Preservative:
The ammonia, which is not attached to hay, acts as a preservative by excluding oxygen from aerobic decomposing microorganisms, like moulds and fungi. Forage can remain covered with ammonia for long periods without problems. Some people recommend that the forage be left uncovered for 3 to 5 days prior to feeding to allow free ammonia to escape. This generally is not necessary, but sometimes animal acceptance may be poor initially if ammoniated bales are not aired out prior to feeding.
Increased digestibility:
Grazing animals derive the vast majority of their energy from plants in the form of carbohydrates. Carbohydrates consist of sugars, starches and fibrous components called cellulose, hemicellulose and lignins.
Animals store excess energy in the form of fat and plants store it as starch, usually in seeds or roots. Dissolved sugars provide the fuel for immediate energy needs of the plant. These two are easily digestible and commonly used by all plant eating animals.
The vast majority of the potential energy in plants, used for grazing, is in the form of cellulose and hemicellulose. Lignin is totally indigestible for animals and provides the structural strength for plants as it grows taller.
Cellulose and hemicellulose are made up out of long chains of sugars, just like starch, but have much stronger chemical bonds holding them together.
Ammonia treatment disrupts these chemical linkages in cellulose and hemicellulose and makes it more digestible. Cellulose digestibility also increases as lignified hemicellulose often encases cellulose. Ammonia treatment also changes the physical characteristics of forage making it more pliable and increases its uptake of water (hydration). Hydration rate has an important role in digestion rate and the faster a forage particle is hydrated, the faster it can be digested.
Increased intake:
It is not known whether treatment increases the fodder’s palatability but faster digestion reduces the time it takes for feed to be processed and excreted ready for more to be taken in. Straw and stover is inherently deficient in many vitamins, minerals and trace elements. These deficiencies, especially vitamin A and sulphur, have to be supplemented to optimise animal production, if these feed sources make up a large part of the animal’s rations.
Materials and methods:
The use of bale tubes or wraps is a huge improvement on the old covered stacks or earth-bunkers used in other parts of the world. Ammonia losses due to leakages into air or ground are eliminated. Large round/ square bales are used in the treatment and are placed in the bale tube or wrapped as per usual. The tube should be placed out in the sun as an increase in heat will speed up the process substantially. Black or green colour plastic will also increase heat inside the tube. Standard bale tubes or bags are the best because they are not as snug fitting and ammonia can spread throughout the tube and penetrate bales more easily.
Urea-solution is made by mixing 10kg of urea (normal fertilizer grade) with 90 liters of cold water until all urea is dissolved (a 10% solution by weight). Mixing urea with cold water will limit the amount of ammonia gas released during mixing and application.
Remember ammonia is a toxic gas and proper ammonia safety precautions must be followed. Work in a well ventilated area up wind from application area. Goggles and gloves should be worn for protection during application. Also have ample clean water available to promptly rinse ammonia off eyes and skin surfaces.
Application rate and equipment: The solution is then applied to hay at a rate of 40 liters per 100kg of dry matter (DM). In small scale operations the solution can be applied, just prior to wrapping, by pouring it into the flat side of a round bale. Solution can also be injected under pressure, through a bale probe (see illustration), into the middle of the bale after it has been wrapped. A bale probe can be made by attaching a 1.5 meter long piece of 15mm diameter
steel pipe to the end of a high pressure hose. The pipe is then closed off at the end, sharpened to a tip and perforated with small holes (2-4mm in diameter) around the sharp tip. A second heavy gauge 20-32mm diameter pipe can be put over the 15mm pipe and used like a waratah (steel stake) rammer to drive probe into a bale.
The bulk tank of a weed sprayer, on the back of a tractor, can be used in larger operations to provide pressure for injection of the urea-solution. The puncture hole in the plastic can then be resealed. The advantage of this method of application is that it can be done later and does not slow the hay contractors down.
Economic Comparison:
To see if the urea treatment of low quality fodder is economically viable, the total costs have to be calculated and compared with the cost of buying in a similar quality (CP content and digestibility) feed. The total cost of treated fodder must include the price of urea (landed on the farm) plus the cost of the plastic tube and wrapping it. If the plastic tube can be used more than once, the cost will be reduced considerably. The cost of urea-treatment must then be added to the value of the untreated forage.
Low quality fodder produced on your farm will save on transport costs and therefore favour treatment. Urea-treatment of low quality forage can easily be done on an average farm without a large investment in additional equipment.
Each farmer or contractor’s situation will vary as to the availability of resources and equipment. Urea-treatment requires no specialized skills or equipment. All equipment that is needed can be found on an average farm or can be hired, for a day, in most rural towns.
