Green hay is produced by harvesting stems, weeds, and other plants before they go to seed. The stems and leaves are then collected, exposed to the sun, and baked to remove most of the moisture, allowing it to be stored for long periods. This process results in high-quality green hay that is rich in nutrients, palatable, and contains up to 20% protein. It is also packed with vitamins such as carotene, which can reach 5-40 mg per kilogram, along with a balanced mineral composition, particularly high in calcium. The digestibility of organic matter in green hay ranges from 46% to 70%, and despite its cellulose content, it is more digestible than similar plant stalks, reaching about 70%-80%. There are two main methods for preparing hay: natural drying and artificial drying.
**1. Natural Drying Method**
The natural drying process occurs in two stages. In the first stage, the plant material is cut and water content is reduced to 38%-40%. During this phase, respiration continues until the cells die, and nutrient loss is significant if the drying process is too slow. To minimize losses, it's crucial to reduce moisture quickly to ensure early cell death. In the second stage, the plants are dried further to 14%-17% moisture, where enzymes break down the plant structure, leading to additional nutrient loss—especially in legumes. Proper drying involves spreading the grass in thin layers under the sun, turning it every 2-4 hours, and piling it once the moisture drops to 40%. Moisture levels can be checked by hand: when twisted tightly, the grass should form a rope without dripping. When held near the cheek, it should not feel cool or damp, and shaking it should produce a crisp sound.
Maintaining the right moisture level is essential to prevent spoilage and preserve quality. Green hay should retain its color and integrity while minimizing nutrient loss.
**2. Artificial Drying Method**
Artificial drying includes both low-temperature and high-temperature methods. Low-temperature drying involves placing the grass in a controlled environment at 40°C–50°C for several hours or using hot air at 15°C for 20–40 minutes. High-temperature drying uses hot air between 500°C–1000°C for 6–10 seconds to dry the grass rapidly.
**Semi-Dry Silage**
In recent years, semi-dry silage has become popular in Europe and North America. Also known as low-moisture silage, this method preserves the original nutritional value of the feed, with only 10%-15% nutrient loss. It is especially effective for legumes like alfalfa and clover, which are difficult to silage using traditional methods.
**Mechanism of Semi-Dry Silage**
Unlike traditional lactic acid fermentation silage, semi-dry silage works by reducing the moisture content to 40%-50%. At this point, the plant cells become more concentrated, increasing osmotic pressure to 50–60 atmospheres. This environment suppresses the growth of spoilage bacteria and prevents fermentation, helping to maintain higher levels of protein and vitamins compared to regular hay or silage.
**Preparation of Semi-Dry Silage**
The best time to harvest for semi-dry silage is during the budding or early flowering stage, with a moisture content of 77%-79%. After cutting, the material is dried quickly to 40%-60% moisture. The silage must be packed tightly and sealed within 48 hours. A plastic sheet is placed over the pile, followed by a layer of straw and 20 cm of soil to prevent air and water intrusion. After 30 days, the silage can be opened and used. Care should be taken to protect the exposed surface to avoid moisture loss.
**Benefits of Semi-Dry Silage**
Compared to traditional hay, semi-dry silage retains more protein and carotene, improving overall nutritional value. For example, semi-dry silage has a crude protein content of 13.07%, compared to 9.61% in hay. Its in vitro digestibility is also higher (56% vs. 50%). Using semi-dry silage for dairy cows increases milk fat percentage and reduces feed costs by 25%-30%, making it a more efficient and cost-effective option for livestock feeding.
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