Almost all of the domesticated animals in lesser developed countries and even some in the developed world exist mainly on poor quality plant materials. Perhaps the most abundant feed in most regions is the straw remaining after harvest of cereal grains. Straw can provide some carbohydrate but is very deficient in other nutrients. Also, because of the high lignin content, digestibility is poor. Methods are available, however, to increase the digestibility of poor quality feeds. One of the most successful procedures to improve digestibility of crude plant material is through treatment with ammonia. This weakens the hard cell walls, allowing better penetration by rumen microorganisms to produce more effective fermentation and liberation of nutrients.
The treatment of fibrous plant materials and even shredded newspapers with steam, alkali, aldehydes or anhydrous ammonia is possible under factory conditions in the industrialized countries. Although this would increase the amount of fodder or fodder substitute available for livestock, it is unlikely to become practical so long as there are ample supplies of quality forage and cereal grains. The situation is quite different in the tropics where residues and by-products abound but better quality feeds are expensive or unavailable. One of the more successful procedures available now to improve the digestibility of straw is urea treatment. Since this requires little in the way of specialized equipment or expense, urea treatment can by applied by even subsistence farmers.
After chopping, the straw is moistened with a urea solution (2.5 to 5%) and usually covered for several weeks. Ammonia, released from the urea, weakens the lignified outer wall and increases the digestibility of the straw. Once treated and if properly covered to preserve anaerobic conditions, the urea-ensiled material can be stored for several months.
Picture courtesy of the FAO Photo Library
A recent FAO electronic conference on tropical feeds contains additional information on urea treatment of poor quality roughage.
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