In modern compound feed production, the application of compound premixes has greatly simplified the production process and saved a significant amount of equipment investment. It plays a crucial role in balancing the nutrition of livestock and poultry feeds, leading to its widespread use. Premixes provide a wide range of nutrients, involve a high level of technical content in their formulation and production, and generally make up 1% to 5% of the total feed. Premixes typically contain vitamins, minerals, and other nutrients. Vitamins, in particular, participate in almost all metabolic reactions in animals as coenzymes and catalysts, maintaining cellular function and enzyme activity while regulating the metabolism of key nutrients. However, due to their structure, rich in unsaturated carbon atoms, double bonds, hydroxyl groups, and other reactive sites, vitamins are highly susceptible to oxidation and reduction, leading to a decrease or complete loss of their activity. The loss of vitamin activity can reduce the nutritional value of the feed, which may adversely affect the growth performance of livestock and poultry or even lead to the onset of nutritional deficiencies. Therefore, the stability of vitamin activity in premixes is critical to feed quality and the growth and health of animals, making it essential to maintain this stability during storage and processing.

1. Major Factors Affecting the Stability of Vitamin Premixes

1.1 Moisture

Moisture is considered the primary factor affecting vitamin stability. Excessive environmental humidity or high moisture content in the carrier and raw materials during processing and storage can destroy vitamin stability. High moisture levels can soften the matrix of vitamin particles, increase oxygen permeability on the matrix surface, and accelerate the oxidative degradation of vitamins and the damaging effects of choline chloride, trace elements, and other chemical reactions on vitamins. Studies have shown that VB1, VB2, niacin, VE, and VC retain high levels of activity after one year of storage under low moisture conditions. However, under high moisture conditions, VB1 retains only 48% of its activity after 21 days, and VC is almost entirely lost. After three months, VB2 levels drop below 50%. To maintain good vitamin stability, the moisture content of premixes should not exceed 7%.

1.2 Temperature

Higher temperatures result in greater loss of vitamins in premixes. Research indicates that vitamin loss is minimal when the temperature is below 10°C. However, when the temperature ranges from 15 to 25°C (room temperature), some less stable vitamins begin to degrade, and when it exceeds 30°C, most vitamins are damaged. This is because vitamins have low melting points and are easily affected by high temperatures. High temperatures provide the energy needed for oxidation-reduction reactions, accelerating vitamin degradation. Furthermore, high temperatures can cause sulfates in premixes to lose part of their crystal water, increasing the moisture content, particularly under high temperature and high humidity conditions, which severely affects vitamin stability. Studies show that after three months of storage under various conditions, VA retention rates are 88% under low temperature and low humidity conditions, 86% under high temperature and low humidity conditions, and only 2% under high temperature and high humidity conditions.

Thus, vitamin premixes must not be stored under high temperature and high humidity conditions.

1.3 Trace Elements and Minerals

Trace elements, particularly copper, iron, and zinc, have a strong detrimental effect on the stability of vitamins. The oxidation-reduction reactions induced by these elements can severely impact vitamin stability. Reports indicate that in the presence of trace elements like Mn2+, Cu2+, Zn2+, and Fe2+, over 80% of VK and 40% of folic acid in vitamin premixes are lost after three months of storage, along with 20% of VB6. Sulfates, such as ferrous sulfate, zinc sulfate, and copper sulfate, are particularly prone to moisture absorption and ionization in water, causing greater damage to vitamins compared to carbonates and oxides. However, carbonates and oxides have lower utilization rates, and sulfates are more cost-effective, making sulfates a double-edged sword in production. Therefore, premix manufacturers often process vitamins, trace elements, and minerals separately into distinct premixes to ensure vitamin stability.

1.4 Carriers and Diluents

The choice of carrier and premix pH value can influence vitamin potency.

1.5 Feed Processing Methods

The production process of compound feeds, including mixing, pelleting, and cooling, involves temperature, friction, pressure, and time, all of which can affect vitamin stability. Studies indicate that VA, VD3, VK3, VB1, and VC are the least stable vitamins in pelleted feeds. When powder and pelleted feeds are stored under the same conditions for three months, it is observed that the retention rate of VA in powder feed is 50% under low temperatures but only 39% under high temperatures. In contrast, the retention rate of VA in pelleted feed is 65% under low temperatures but only 20% under high temperatures. This indicates that vitamins in pelleted feeds are more resistant to low temperatures, while those in powder feeds are more resistant to high temperatures.

1.6 Other Factors

Choline chloride, with its strong hygroscopicity and alkalinity, can damage other vitamins, particularly VK, VB1, VB6, pantothenic acid, and biotin, especially in conjunction with trace elements. Some feed ingredients contain anti-vitamin factors, such as lipoxygenase in raw soybean meal, which can indirectly destroy VA and carotene, and anti-VB6 factors in flaxseed. Certain drugs also affect vitamin stability, such as amprolium, which antagonizes VB1, and sulfonamide potentiators, which antagonize folic acid. Light or ultraviolet exposure can severely damage vitamins VA, VD3, VE, VK, VB1, VB2, VB6, VB12, VC, and folic acid. As storage time increases, all vitamins experience some loss, with unstable vitamins such as biotin, VB12, and folic acid losing 10% to 15% after more than three months of storage.

2. Measures to Improve the Stability of Vitamin Premixes

2.1 Choosing Stable Vitamin Types

Selecting stable vitamin raw materials can effectively reduce losses during production and storage. For example, VA retinyl palmitate and acetate, VK3 dimethylpyrroquinone bisulfite (50% MPB), nitrothiamine for VB1, pyridoxine hydrochloride for VB6, L-ascorbic acid calcium for VC, nicotinamide for niacin, calcium pantothenate, and riboflavin acetate for riboflavin are recommended.

2.2 Proper Selection of Carriers and Diluents

When selecting carriers and diluents, factors such as bulk density, moisture content, particle size, segregation characteristics, pH value, fat content, flowability, and caking should be carefully considered. In production, carrier pH should be controlled between 6 and 8, and moisture content should be kept below 12%. Common carriers or diluents for vitamin premixes include bran, corncob powder, cornmeal, and rice husks, which have similar density and particle size to most vitamins.

2.3 Appropriate Overdosing

To ensure the stability of vitamins in compound feed, vitamins should be overdosed according to storage conditions, turnover cycles, production types, and environmental factors. For example, when producing compound premixes stored for more than three months, vitamin overdosing is often necessary, with typical overdosing rates of 15% to 25% for VA, 5% to 15% for VD, 10% for VE, and 10% for folic acid. In general, overdosing in complete feeds ranges from 5% to 10%.

2.4 Adding Antioxidants and Mold Inhibitors

Adding appropriate antioxidants to vitamin premixes can slow down vitamin oxidation and maintain potency. Common antioxidants include ethoxyquin, BHT, BHA, and citric acid. Since feed is prone to mold growth in humid environments, adding appropriate mold inhibitors, such as propionic acid, sodium propionate, and sorbic acid, is also crucial for maintaining vitamin stability.

2.5 Reducing Storage Time and Improving Storage Conditions

Vitamin storage environments should be kept cool, dry, dark, and sealed. The ideal temperature is 15 to 26°C, with humidity controlled below 70%. Premixes should be used immediately after opening. Minimizing the storage time of premixes or compound feeds is essential, with vitamin premixes generally required to be used within one month and no longer than three months.

In summary, many factors affect the stability of vitamin premixes. During production and storage, it is important to minimize these factors as much as possible to prevent vitamin loss, save production costs, and ensure the quality of premixes and compound feeds.