Alkaline treatment of straw, such as using sodium hydroxide, ammonia, lime, or urea, is an effective method to improve its digestibility and nutritional value. This process works by breaking down the alkali-labile ester bonds between cellulose, hemicellulose, and lignin, which helps dissolve part of the hemicellulose and lignin. As a result, the cellulose swells, allowing rumen fluids to penetrate more easily. Strong bases like sodium hydroxide can break down up to 50% of the lignin, making the straw more accessible for microbial digestion.
Chemical treatments not only enhance the digestibility of straw but also improve its palatability, leading to increased feed intake. Among the various methods, alkalization and ammoniation are the most commonly used techniques in practice.
**First, Alkali Treatment of Straw**
Alkali treatment involves soaking straw in an alkaline solution to loosen the plant cell walls, making it easier for digestive enzymes to access. This treatment can increase the digestibility of straw beyond 50%, while also boosting feed intake by 20% to 45%.
1. **Sodium Hydroxide Treatment**: For 100 kg of chopped straw, spray 6 kg of a 1.6% sodium hydroxide solution evenly, then stack it for 6–7 hours. Afterward, rinse the straw thoroughly with clean water to remove the alkali, form it into cakes, and feed it in portions. This process increases the organic matter digestibility from 42.4% to 62.8% and crude fiber digestibility from 53.5% to 76.4%.
2. **Lime Solution Treatment**: Use 100 kg of chopped straw, mix it with 3 kg of quicklime or 4 kg of slaked lime, along with 0.5–1 kg of salt and 200–250 liters of water. Soak the mixture for 12 hours or overnight, then drain for 24 hours before feeding without washing.
**Second, Ammoniation Treatment of Straw**
Ammoniation is another low-cost and highly beneficial method for processing straw. The principle behind this technique is that ammonia dissolves in water to form ammonium hydroxide, which softens the straw and expands the lignified fibers. This improves the permeability of the straw, allowing better contact with digestive enzymes and enhancing cellulose digestion. Additionally, ammonia reacts with the organic matter in straw, forming ammonium salts and complexes that increase the crude protein content from around 4% to over 8%. This significantly boosts the nutritional value of the feed.
After ammoniation, the digestibility of straw can increase by about 20%, and feed intake may rise by a similar amount. It also improves the palatability and feeding speed of dairy cows, increasing the total nutritional value to approximately 0.4–0.5 feed units. In other words, 1 kg of ammoniated straw has the same nutritional value as 0.4–0.5 kg of oats. Because of these advantages, ammoniation has gained widespread use in ruminant livestock farming.
There are three main methods of ammoniation depending on the nitrogen source used:
1. **Liquid Ammoniation Method**: Chopped straw is moistened to 15–20% moisture, mixed well, and placed in a plastic tube with holes. Anhydrous ammonia is introduced at 3% of the straw’s weight. The straw is then sealed and left for 2–4 weeks at 20°C (shorter in summer, longer in winter). Once dried, the ammonia smell disappears naturally, and the straw can be fed after being crushed.
2. **Urea Ammoniation Method**: Urea is added at 3% of the straw’s weight. For 100 kg of straw, 5 kg of urea is dissolved in 60 liters of water and sprayed evenly. The straw is stacked, covered with plastic, and stored under suitable conditions. If urea is unavailable, ammonium bicarbonate can be used instead, though it requires a higher dosage due to its lower nitrogen content (17%).
3. **Ammonia Water Ammoniation Method**: Straw is placed in containers (such as tanks or silos), and 3% ammonia water is sprayed at a ratio of 1:1. For every 100 kg of dry straw, 41 liters of 5% ammonia water is used. After filling, the container is sealed and left for 2–3 weeks at 20°C (about a week in summer, 4–8 weeks in winter). The straw is then removed, dried, and fed.
In practice, liquid ammonia and urea ammoniation methods have shown the best results. However, liquid ammonia requires high-pressure equipment, increasing costs and operational risks. Urea ammoniation, on the other hand, is safer, simpler, and more suitable for small-scale farmers.
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