Straw can be treated with alkaline substances such as sodium hydroxide, ammonia, lime, or urea to break the ester bonds between cellulose, hemicellulose, and lignin. This process helps dissolve part of the hemicellulose and lignin, allowing cellulose to swell and making it easier for rumen fluids to penetrate. Strong bases like sodium hydroxide can hydrolyze up to 50% of the lignin, significantly improving the digestibility of the straw. In addition to enhancing digestibility, chemical treatments also improve the taste and increase feed intake. Among these methods, alkali treatment and ammoniation are the most widely used.
Alkali treatment involves soaking the straw in an alkaline solution, which loosens the plant cell walls and makes them more accessible to digestive enzymes. As a result, the digestibility of the straw can increase by over 50%, and feed intake may rise by 20% to 45%. One common method is using a 1.6% sodium hydroxide solution. For every 100 kg of chopped straw, 6 kg of this solution is sprayed evenly, then the straw is stacked for 6–7 hours before being washed thoroughly with clean water. After drying, it is formed into cakes and fed in portions. This treatment increases organic matter digestibility from 42.4% to 62.8% and crude fiber digestibility from 53.5% to 76.4%.
Another method is lime treatment, where 100 kg of chopped straw is mixed with 3 kg of quicklime or 4 kg of slaked lime, along with 0.5 to 1 kg of salt, and 200 to 250 liters of water. The mixture is soaked for 12 hours or overnight, then drained for 24 hours before feeding without washing.
Ammoniation is another effective technique that uses ammonia to soften the straw, expand the lignified fibers, and enhance permeability, allowing better contact with digestive enzymes. Ammonia also reacts with the straw’s organic matter to form ammonium salts and complexes, increasing its crude protein content from around 4% to over 8%. This significantly boosts the nutritional value of the feed. After ammoniation, digestibility improves by about 20%, and feed intake increases similarly. The palatability and feeding speed for dairy cows also improve, with the nutritional value of ammoniated straw equivalent to 0.4–0.5 kg of oats per kilogram.
There are three main types of ammoniation: liquid ammoniation, urea ammoniation, and ammonia water ammoniation. Liquid ammoniation involves spraying the straw with water to achieve a moisture content of 15–20%, then introducing anhydrous ammonia at 3% of the straw’s weight. The straw is sealed for 2–4 weeks, depending on temperature, and after drying, the ammonia smell disappears naturally.
Urea ammoniation is a simpler and safer method. Urea is dissolved in water and sprayed onto the straw at 3% of its weight. The straw is then stacked and covered with plastic film. This method is especially suitable for small-scale farmers due to its ease of use and lack of need for special equipment. If urea is scarce, ammonium bicarbonate can be used instead, though it requires a higher dosage due to its lower nitrogen content.
Ammonia water ammoniation involves filling containers with straw and spraying 3% ammonia water at a ratio of 1:1. At a 5% concentration, 41 liters of ammonia water are used per 100 kg of dry straw. After sealing for 2–3 weeks (depending on temperature), the straw is removed, dried, and fed.
While liquid ammoniation provides excellent results, it requires high-pressure equipment, increasing both cost and safety risks. Urea ammoniation, on the other hand, is more practical and widely adopted, especially among small-scale dairy farmers. Overall, these chemical treatments offer a cost-effective way to improve the nutritional value and digestibility of straw, making it a valuable feed source for ruminants.
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