The application effects of feed enzyme preparations are undeniable. They not only improve the digestion rate and utilization efficiency but also enhance the productivity of livestock and poultry. Moreover, they reduce the nitrogen and phosphorus intake in animal excreta, protecting the soil from pollution. Therefore, feed enzyme preparations, as a type of high-efficiency, non-toxic, environmentally friendly "green" product, have broad prospects for application in the 21st century.

Although the role of enzyme preparations is widely recognized, the specificity of enzyme production, such as using different strains, different production methods (solid-state fermentation or liquid fermentation), and significant differences in the determination conditions of the final product, has brought certain difficulties to users of enzyme preparations. It is challenging to simply judge which enzyme preparation product is suitable based on appearance. When deciding which type of enzyme preparation to use, at least the following factors should be considered:

Firstly, consider its composition, mainly focusing on factors such as the type of grains and proteins, the ratio of grains and proteins, and the level of anti-nutritional factors in grains and proteins. The second consideration factor is the animal itself, especially the age and breed.

Generally speaking, the following combinations can be recommended: use xylanase in arabinoxylan-rich feeds; use β-glucanase in β-glucan-rich feeds; use amylase and protease in feeds for young animals.

Characteristics of Different Enzyme Preparations and Their Substrates:

One of the main characteristics of enzyme action is substrate specificity, so one should first have a preliminary understanding of the substrate it acts upon. Currently, domestic enzyme preparations mainly include enzymes that digest non-starch polysaccharides, amylase, protease, etc. This section will elaborate on the characteristics of the above non-starch polysaccharides and their corresponding substrates.

Non-starch Polysaccharides (NSP) mainly include xylan, arabinan, galactan, mannose, and glucan. NSP has strong anti-nutritional effects. These anti-nutritional effects significantly affect their use. In wheat, naked oats, barley, and the processing by-products used, arabinoxylan (AX) is the main anti-nutritional factor. In barley and oats, the anti-nutritional factors mainly consist of β-glucan and arabinoxylan.

1.1 Arabinoxylan:

Arabinoxylan is the main component of NSP. Arabinoxylan is a xylan molecule connected by β-(1,4) glycosidic bonds, forming a skeletal structure. This linear long-chain structure of xylan molecules is its basic framework. Depending on the source, different components may be connected to its straight chain, forming linear side chains.

The most well-known property of arabinoxylan is its ability to increase the viscosity of chyme due to its strong water absorption capacity. The increased viscosity makes it difficult to mix with digestive enzymes and bile salts, affecting the absorption efficiency of nutrients. This also leads to increased microbial activity. There is reason to believe that this is an important reason why animals fed with high arabinoxylan content in their diet have poorer growth performance. One possible explanation is that these microbes and their hosts compete for nutrients. Intestinal microbes can also transport bile salts that play an important role in fat digestion. Another important anti-nutritional effect of AX is its formation as a cell wall component, wrapping a large amount of readily available nutrients such as starch and protein, or forming chemical bonds with nutrients. These wrapped nutrients cannot be fully utilized by the animal's intestines.

1.2 Xylanase:

Xylanase is currently the most widely used enzyme. From the source, there are fungal xylanases and bacterial xylanases. In terms of action mode, they include exo-xylanases and endo-xylanases.

Endo-xylanase can break down xylan polymers into shorter chains. This endo activity quickly reduces the viscosity of chyme and releases wrapped nutrients. Therefore, this enzyme is the most important enzyme to eliminate the anti-nutritional effects of AX. Exo-xylanase can only act at the end of AX.

1.3 β-Glucan:

β-Glucan is a polymer formed by connecting D-glucose through β-(1-3) and β-(1-4) glycosidic bonds. Since they are water-soluble, they do not form complex structures.

At low concentrations, β-glucan only interacts with water molecules, trapping water. But when the concentration increases, they react with each other to form a network structure (gel). Therefore, feeds with high concentrations of β-glucan will increase the viscosity of the intestinal contents. The anti-nutritional effects of increased viscosity in arabinoxylan have been detailed.

1.4 β-Glucanase:

Similar to arabinoxylanase, to eliminate the viscosity effect of β-glucan, its long chain needs to be hydrolyzed into shorter chains. The most effective method is to use endo-β-glucanase.

1.5 Cellulose:

Cellulose is a linear polymer composed of D-glucose connected by β-1,4 glycosidic bonds. Each cellulose molecule contains 800-1200 glucose molecules, and hydrogen bonds can be formed between intramolecular, intermolecular, and between the molecular chain and the surface molecule. Common feeds like grains, legumes, cereals, and forages contain a large amount of cellulose, often combined with hemicellulose, pectin, etc. Except for ruminants, which can utilize some cellulose, monogastric animals like pigs, etc., cannot utilize cellulose.

1.6 Cellulase:

Cellulase is a complex enzyme system composed of various hydrolytic enzymes. According to the differences in the functions of each enzyme, it is divided into the following three categories: endoglucanase, exoglucanase, and β-glucosidase. Cellulase completes hydrolysis under the synergistic action of these 3 types of enzymes.

Cellulase can break the plant cell wall, exposing the protoplast inside for further degradation. It improves the digestion rate of intracellular substances, thereby effectively increasing the available energy value and supplementing the deficiency of endogenous enzymes in herbivores. Adding cellulase preparations can significantly improve the digestibility of crude fiber in herbivores. Moreover, for monogastric animals, cellulase can improve the digestive tract environment, increase acidity, and activate pepsinogen. Eliminate anti-nutritional factors, reduce material viscosity, promote the diffusion of endogenous enzymes, and increase nutrient digestion and absorption.

1.7 Mannan:

Mannan is a type of hemicellulose, which is mainly composed of mannose. Its content in copra is very high, and its content in soybean meal is higher than that in other commonly used feeds.

For poultry and pigs, mannan reduces the digestibility of meal. Even at a low concentration, mannan will reduce the absorption rate of glucose in the intestines, resulting in reduced carbohydrate metabolism through affecting insulin secretion and insulin-like growth factor production. It also reduces the absorption of fats and amino acids, reduces water absorption, and increases fecal water content.

1.8 Mannanase:

Mannanase is one of the hemicellulases. It can effectively break down mannan in meals to produce manno-oligosaccharides and other substances. Although manno-oligosaccharides cannot be directly absorbed by the animal body, they can participate in the animal's neuroendocrine system and affect metabolism. The roles of mannanase include: improving the energy utilization rate of meals, reducing the variability of animal weight. The smaller the animal's weight, the easier the enzyme's effect can be manifested, effectively preventing bacterial and parasitic invasions of the intestines, and improving the health level of animals.

1.9 Pectin:

Pectin is a polysaccharide component existing in plant tissues, mainly composed of galacturonic acid and its methyl ester, which together with cellulose play a structural role in plants.

1.10 Pectinase:

Pectinase contains esterase, hydrolase, and lyase, which respectively have ester, hydrolytic, and cleavage effects on pectin. They produce galacturonic acid, oligogalacturonic acid, unsaturated galacturonic acid, oligosaccharides, etc., eventually breaking down plant structures and releasing nutrients.