Precautions for Feed Mold Prevention and Detoxification

Mycotoxins are secondary metabolites produced by fungi. Common molds include Aspergillus, Fusarium and Penicillium, which can grow during crop growth and harvest as well as on crops after processing. Mycotoxins not only have toxic effects on livestock and poultry, but can also endanger human health through the food chain. At present, the most critical measures for preventing and controlling the harm of mold and mycotoxins are the two links of mold prevention and detoxification of feed.

I. Feed Mold Prevention

1. Reduce contamination. When purchasing raw materials, inspection and acceptance should be strengthened to prevent moldy raw materials from entering the factory, keep feed warehouses and processing and transportation equipment clean and free of contamination, regularly inspect and clean the parts of the production line where feed is likely to remain for a long time, and thoroughly clean up any moldy and caked feed.

2. Control the moisture content of raw materials and keep the environment dry. Generally, the moisture content of feed raw materials is required not to exceed 13%, and feed raw materials with excessive moisture content should be dried in the sun in a timely manner. The warehouse for storing feed should be dry; during storage, a base should be placed underneath and gaps should be left above and around to allow air circulation. For those stored for a longer time, moisture monitoring should be carried out regularly, and measures should be taken promptly if the moisture content exceeds the standard.

3. Appropriately add mold inhibitors and antioxidants. Mold inhibitors can inhibit the reproduction, growth and toxin production of molds by destroying the mold cell wall or the acids inside the cells. When the moisture content of feed is higher than the upper limit standard for safe storage moisture content, the addition of mold inhibitors may be considered. At present, the mold inhibitors used more often are propionic acid and its salts (calcium propionate, sodium propionate and potassium propionate). The addition amount of propionic acid is 0.3% of the feed, and the addition amount of calcium propionate is 0.2%-0.5% of the feed amount. Whether to use mold inhibitors in feed and the amount used are mainly determined according to the season and moisture content. In dry and cool seasons such as autumn and winter, when feed moisture is below 11%, mold inhibitors are generally not necessary; when moisture exceeds 12%, mold inhibitors should be used, and when feed moisture is relatively high and in hot and humid seasons, the amount of mold inhibitor used should also be increased. The molding process of feed is also accompanied by the oxidation process of nutrients in the feed. Generally, mold inhibitors should be used together with antioxidants to form a complete mold-prevention and antioxidant system in order to effectively prolong the storage period.

4. Reasonable storage of feed. When loading and transporting feed, prevent rain and sun exposure. The feed storage warehouse should be ventilated, cool, dry and located on high ground, with supports at the bottom to isolate it from the ground, and it should be regularly disinfected, cleaned and protected against rats. Stacking should be standardized. If the ambient temperature is higher than 10°C, the stacking height should not exceed 14 layers (bags). The feed stack should maintain a certain distance from windows and walls, and attention should be paid to the fact that the storage time should not be too long.

II. Feed Detoxification

When feed becomes moldy, especially when a large amount of feed raw materials become moldy, discarding all of it will cause heavy losses. However, if the mold is very serious, it should be discarded because its nutrients have been severely lost. For mildly moldy feed and raw materials, different methods can be used for detoxification treatment according to the specific situation. Detoxification methods generally include physical detoxification, chemical detoxification, enzymatic hydrolysis and adsorption.

1. Physical detoxification and chemical detoxification. Physical detoxification methods mainly include washing with water, removal by picking, degerming and detoxification, solvent extraction, detoxification by heating and irradiation, etc.; chemical detoxification mainly uses alkali or oxidants for treatment and detoxification. The many detoxification methods mentioned above are not suitable in practical application or for the current feed industry and breeding industry, because their operation is not only difficult, but chemical detoxification treatment often reduces the nutritional quality and palatability of feed.

2. Enzymatic hydrolysis. This mainly involves selecting certain enzymes and using their degradation effects to destroy mycotoxins or reduce their toxicity. Compared with physical and chemical methods, enzymatic degradation treatment causes less loss of and impact on feed nutrients, but three problems arise in practical application: First, enzymes are not heat-resistant and are easily inactivated at high temperatures, while the production process of finished feed, especially the pressing of pelleted feed, requires high temperatures. Second, the cost of using enzymatic detoxification is relatively high and is generally difficult to accept. Third, when using enzymes to degrade the toxicity of mycotoxins, some mycotoxins require a complete enzyme system to completely degrade their toxicity. For example, when degrading zearalenone, some enzymes only convert it into another substance, and this converted substance is still toxic and requires a series of enzymes to completely degrade it into a non-toxic substance. This series of enzymes is still in the research stage.

3. Adsorption method. That is, a method of detoxification by adding mycotoxin adsorbents to feed. This method is still relatively feasible (it is already commonly used abroad). In actual production, suitable adsorbents should be selected, and they are required to both effectively reduce the harm of mycotoxins to animals and not cause negative effects on animal growth. An ideal adsorbent should have the ability to adsorb different types of mycotoxins; be effective at low usage amounts; be able to mix quickly and uniformly in feed and have strong stability during processing, granulation, expansion and storage; have no adsorption effect on vitamins, trace elements, drugs and other nutrients; have high stability over a wide pH range and be biodegradable after excretion; and itself should contain no contaminants.

At present, the mycotoxin adsorbents with relatively good detoxification effects in feed mainly include aluminosilicates, organic substances (such as yeast cell walls) and other resins (such as cholestyramine). Natural aluminosilicates, such as zeolite, montmorillonite, diatomite and kaolin, have good adsorption capacity especially for aflatoxins, but their adsorption capacity for toxins such as zearalenone, ochratoxin and trichothecenes is insufficient. Esterified glucomannan (EGM) is a new type of mycotoxin adsorbent and is a functional carbohydrate extracted from yeast cells. Its surface is rich in cavities of different pore sizes, which are used to capture different types of mycotoxins over a large area. Therefore, EGM has strong adsorption effects on many kinds of mycotoxins, and the adsorbed mycotoxins are not easily dissociated. It has no significant side effects on other nutrients in feed and may also have positive effects on other physiological functions of animals. It is a broad-spectrum mycotoxin adsorbent with great potential.