Wheat straw

Useful reference: 393 
 
Various types of crop production (cereals, sugar cane, etc.) result in large quantities of low-digestibility roughages, which are thus eaten far less voluntarily because of their slow passage through the alimentary canal. Only limited use can be made of straws in ruminant nutrition. Animals spend more energy in chewing and digesting such roughages than they gain from them. 
Often the digestibility of poor roughage is limited not by the lignification but by the low nitrogen content. The minimum crude protein requirement for efficient lignocellulose breakdown of roughages fed as the sole diet is claimed to be 3.8-5%. In many cases the digestibility and the rate of rumen passage can be increased by supplementing the feed with protein concentrate or urea plus minerals. In some cases it is economical to increase the nutritive value of poor roughages by physical or chemical treatments. 

 
PHYSICAL TREATMENTS. Roughages can be treated by soaking, boiling, fermenting or grinding. Grinding is the preferred method as the others generally give poor results. However, grinding the roughage deprives the animal of the opportunity to reject the fibrous parts and also reduces the digestibility of the feed, although this disadvantage is usually counterbalanced by a higher voluntary feed intake. If, for instance, wheat straw is ground, even rather coarsely, the intake increases by 20-30% because of faster passage through the rumen. This is illustrated by the results of an experiment with late timothy (ref. 207): 

  
      DIGESTIBILITY INTAKE OF
      OF CRUDE FIBRE DIGESTIBLE ENERGY
Long form...................  46%90 kcal/W kg^0.75
Ground and pelleted......... 31%175 kcal/W kg^0.75
  
 
Such increases in digestible energy intake can produce dramatic changes in beef production of more than 50% increases in daily gains for animals on all-roughage diets. It should be noted that the increased intake of digestible energy raises the protein requirement as well. When ground forage is mixed with concentrates, grinding tends to eliminate the difference in forage quality. 

  
 
CHEMICAL TREATMENTS. Treating straw with alkali can give a product of considerable nutritive value. The usual methods require large quantities of water and are therefore impracticable in areas where water supplies are limited. The process consists of soaking the straw in ten times its weight of 1.3% sodium hydroxide solution at ambient temperature for about twenty-four hours. The liquid is then drained off to be used for another batch of straw. An average of 7-8 kg of caustic soda is consumed by 100 kg of straw. The straw is washed after treatment until it is free of alkali. This treatment increases the organic matter digestibility of wheat straw from 46% to more than 70%. As straw so treated is loose, less energy is lost in chewing and digestion. The straw is palatable and can be consumed in large quantities by livestock. Beef cattle can be fed up to 20 kg of treated straw per day, dairy cows up to 15 kg, young heifers up to 10 kg and sheep up to 3 kg. 

Attempts have been made to reduce the amount of water required for the process, so that 100 kg of straw, for example, can be mixed with only 300 litres of water and 6 kg of sodium hydroxide. After treatment the straw is washed according to the principle of chromatography (countercurrent), whereby the stream of water meets the flow of straw. The straw and the water are introduced at opposite ends of a container. The water passes through the straw and vice versa, and each is extruded at a point as far as possible from the point of introduction; thus the dirtiest water meets the dirtiest straw and the cleanest water meets the cleanest straw. With this method a total of 400 litres of water is sufficient to reduce the alkali content to an acceptable level. Chromatographically treated wheat straw has a crude fibre digestibility of about 90%. If higher costs for chemicals are acceptable, the alkali can be neutralized with acetic acid rather than washed out. However, the high level of sodium in such materials may cause problems if fed in large amounts. Neutralization through ensiling also seems promising. 

A recent approach is to spray low concentrations of alkali on the feed (4 kg of sodium hydroxide per 160 kg of chopped straw) and to allow it to slake before feeding. The sprayed straw is pelleted so that the alkali comes in close contact with the fibre. The pellets are not neutralized before feeding. Another modern method is that of treating the straw for fifteen minutes in a hot (80- 90 C) solution of sodium hydroxide. The liquid is then pressed out of the treated straw before it is dried in a grass drier. The acid hot gases (carbon dioxide and sulphur dioxide) in the drier neutralize the straw. 

Treatment with gaseous ammonia also increases the digestibility of straw and enriches it with nitrogen. In a simple application of this method the straw is baled loosely and placed on a plastic sheet, after which the straw is tightly covered with plastic and gaseous ammonia (3-4% of the weight of the straw) is let in through a hose. The straw can be used after three to eight weeks, when the plastic is removed and the ammonia aired off. 

     As % of dry matter
 
    DMCPCFAshEENFECaPRef
Wheat straw, alkali 
treatment  18.92.953.55.01.537.1  221
 
 
       Digestibility (%)
 
     AnimalCPCFEENFEMERef
 
Alkali-treated strawSheep0.077.039.057.02.29221
 
 

References

221, 393

Abstracts

Buffaloes(135), Camels(622), Cattle(275), Cattle(284), Cattle(632), Pigs(2), Pigs(294), Pigs(664), Sheep(271), Sheep(677), Straw(622), Straw(677), Urea-ammonia treatment(135), Urea-ammonia treatment(677)