In recent years, my country’s animal husbandry and feed industry have developed rapidly, and the volume of livestock and poultry aquaculture has surged, resulting in a continued increase in feed consumption and an increasingly prominent conflict between humans and animals competing for food. Corn-soybean meal type diet is the dominant feed structure in my country, in which the amount of soybean meal accounts for more than 20% of the raw grain and more than 25% of the total cost of raw materials. China is one of the world’s largest soybean importers. In 2021, my country’s soybean imports were approximately 96.52 million tons, mainly from the United States, Argentina and Brazil. my country’s annual soybean output is about 16.4 million tons, which is seriously insufficient in supply. In addition, the average price of my country’s soybean imports in 2021 is 554.7 US dollars/ton, an increase of 40.79% compared with the average price in 2020. The continued high fluctuation of soybean meal prices has also led to a surge in breeding costs. Therefore, finding feed ingredients with high nutritional value and low cost to replace part of soybean meal has become the key to reducing breeding costs and ensuring breeding benefits.

1 Nutrients of mixed meal

Miscellaneous meal generally refers to other cakes except soybean meal, including rapeseed meal, peanut meal, cottonseed meal, sesame meal, sunflower meal, linseed meal, palm kernel meal, coconut meal, flaxseed meal, rubber seed meal and oil Rock bean meal (a by-product of oil extraction from rock bean), etc., has the characteristics of high yield, high nutritional value, low cost, etc., and has broad development prospects. The main nutritional components of soybean meal and common miscellaneous meal are shown in Table 1. The crude protein (CP) content of cottonseed meal, peanut meal, sesame meal and sunflower meal is similar to that of soybean meal. The CP content of rapeseed meal and linseed meal is about It is about 80% of soybean meal. In addition, the content of vitamins and minerals in different mixed meal varies greatly, and rapeseed meal is rich in iron, manganese, zinc, and selenium, of which the selenium content is 0.15%, which is much higher than that of soybean meal (0.06%); the B content of peanut meal It is rich in vitamin B2, of which vitamin B2 is 11.0 mg/kg, which is much higher than soybean meal (3.0 mg/kg).

2. Restrictive factors in the use of mixed meal

2.1 Antinutritional factors

Feed antinutritional factors (ANF) are commonly found in plant feeds, which can affect the utilization of nutrients such as protein, energy, and vitamins in the feed, and reduce the growth rate and health level of livestock and poultry. ANF can be divided into 6 categories according to its functional characteristics.

① Reduce protein digestibility, such as protease inhibitors, lectins, tannins and saponified substances;

② Reduce carbohydrate digestibility, such as amylase inhibitors, phenolic compounds and gastric flatulence factors;

③ Reduce the utilization rate of minerals and trace elements, such as phytic acid, oxalic acid, gossypol and thioglucosides, etc.;

④ Vitamin compounds, such as dicoumarol, thiamine enzyme, lipoxygenase, etc.;

⑤ Immune system stimulants, such as antigen proteins, etc.;

⑥Other ANF can affect the utilization of various nutrients, such as water-soluble non-starch polysaccharide (NSP), etc.

ANF in common mixed meal mainly includes thioglucosides, gossypol, phytic acid, tannins and protein inhibitors, among which the hydrolysis products of thioglucosides are thiocyanate, isothiocyanate and oxazolidine sulfide. Ketones can cause changes in thyroid morphology and function, thereby affecting the growth performance and health of livestock and poultry. Common removal methods include microbial detoxification, adding exogenous enzymes for detoxification, etc. Cottonseed meal often contains gossypol, phytic acid, tannins, etc. , among which free gossypol (FG) is a poison to animal cells, blood vessels and nerves, interfering with the normal physiological functions of animals. Common removal methods include microbial fermentation, alkali treatment and heat treatment. Other ANFs, such as phytic acid, tannins and protease inhibitors, can cause animals to reduce the utilization of nutrients and can be removed by methods such as heating, fermentation and enzymatic hydrolysis.

2.2 Amino acid balance problem

Different sources of miscellaneous meal have different amino acid content. The amino acid composition of some miscellaneous meal shows that the amino acid composition of miscellaneous meal is comprehensive and basically includes the main amino acids in soybean meal. However, most of the miscellaneous meal has an unbalanced amino acid ratio. Among them, peanut meal, cottonseed meal and Sesame meal has a higher arginine (Arg) content, and peanut meal has the highest Arg content, about 4.88%. In addition, sesame meal is rich in methionine (Met) and tryptophan (Trp), and the Met content exceeds 0.8%, ranking first among cakes; but the Lys content is lacking, only 30% of soybean meal; and the ratio of Lys to Arg (0.82:2.38) Serious imbalance.

A study using mice as an experimental model found that the protein nutritional value of sesame meal (relative to casein) is only 47%, but adding 0.2% Lys can increase it to 94%. Adding 0.2% Lys + 0.1% Leu + 0.1% Met can increase the nutritional value of sesame meal to 94%. Increased to 102%. Since soybean meal is rich in Lys but lacking in Met, adding 0.4% to 0.5% Lys or soybean meal to sesame meal can significantly improve the growth performance of poultry. By rationally utilizing the complementarity of miscellaneous meal and combining various kinds of miscellaneous meal, the nutritional level will be more balanced, which will also help to improve the nutrient utilization rate of miscellaneous meal, improve feed quality and reduce feed cost.

2.3 Toxin problem

Mycotoxins are toxic secondary metabolites produced by fungi (molds). Feed contaminated by molds and mycotoxins can cause feed deterioration and livestock and poultry poisoning. Common mycotoxins currently include aflatoxins (AF), fumonisins, ochratoxins, trichothecenes, zearalenone (ZEN), butenolide, patulin and vomitin Toxins (deoxynivalenol, DON), etc.

Huang Guangming et al. tested feed and feed raw material samples collected from 14 provinces (cities) including Beijing and Hebei, and found that the most serious violations of aflatoxin B1 (AFB1) were cottonseed meal, peanut meal, rapeseed meal and other miscellaneous meals.

Lei Yuanpei et al. used immunoaffinity column-high performance liquid chromatography to detect feed and feed raw materials and found that the detection rate of AFB1 in mixed meal was 100%, the detection rate of ZEN was 75%, and the detection rate of DON was 96.3 %.

Zhang Yong et al. used immunoaffinity column-high performance liquid chromatography to test feed and feed raw materials in 2021, and found that the AFB1 exceedance rate of mixed meal was the highest (14.93%). It can be seen that mold contamination of feed is widespread, and trace amounts of mycotoxins are Can cause great harm to livestock, poultry and people.

Pigs are prone to mold poisoning after eating feed contaminated by mold. In mild cases, it will affect their later growth and development and breeding and reproduction, and lead to a decline in the body’s immune function. In severe cases, it will directly lead to death. Therefore, when using mixed meal, mycotoxin testing should be carried out in a timely manner, and mildew prevention and detoxification treatments should be strengthened to ultimately ensure human food safety by ensuring feed hygiene and livestock and poultry health and safety.

2.4 Processing methods

At present, mixed meal is mostly processed by methods such as solvent extraction and pre-pressure extraction. High pressure and heat treatment will lead to the loss of nutrients in the mixed meal, protein denaturation and reduced utilization of amino acids (especially Lys). Therefore, it should be prevented during production. Excessive thermal processing. By comparing the effects of high-temperature pressing and pre-pressing extraction on the chemical components of rapeseed meal, Li Bo et al. found that crude fiber (CF), neutral detergent fiber, acid detergent fiber, and acid detergent fiber in high-temperature pressed rapeseed cake. The content of fiber and acid washed lignin was significantly higher than that of pre-pressed extracted rapeseed meal.

In addition, the CF content of miscellaneous meal is related to the degree of shelling during the oil production process. The CF content of unhulled miscellaneous meal is generally high and the effective energy value is low. For example, the CF content of cottonseed meal is 17%, and the CF content of sunflower meal with shell is 17%. The content reaches 30.7%. Too high CF in mixed meal cannot be easily digested and utilized by monogastric animals. Instead, it dilutes the nutrient concentration of the meal itself, and also affects the digestion and absorption of other nutrients, showing anti-nutritional effects.

3. Technology for improving quality and efficiency of mixed meal

3.1 Fermentation

There have been many studies on microbial fermentation technology in eliminating ANF in mixed meal and improving nutritional value. Zhang et al. used Candida capsulatus ZD-1, Candida tropicalis ZD-3, Saccharomyces cerevisiae ZD-5, Aspergillus terreus ZD-6, Aspergillus oryzae ZD-7 or Aspergillus niger ZD-8 to ferment cottonseed meal and found that the microorganism Fermentation can significantly reduce the FG level in cottonseed. Among them, Candida tropicalis ZD-3 has the lowest FG content after fermentation, and the detoxification rate reaches 94.6%.

Qin et al. found that replacing 10% of soybean meal with ordinary cottonseed meal during the entire growth and fattening period of pigs (65-162 days) can significantly reduce growth performance, while replacing 15% of soybean meal with fermented cottonseed meal (FCSM) When soybean meal is used, it has no significant adverse effects on growth performance and can reduce feed costs per unit weight gain. The reason may be that ANF is significantly reduced after cottonseed meal is fermented by microorganisms. At the same time, the detoxification fermentation process produces a large number of probiotics, which can improve intestinal health.

Ding Chao et al. used FCSM to replace 25% and 50% of soybean meal in the diet, and found that the unit weight gain cost of growing pigs in the 50% soybean meal replacement group was the lowest, followed by the 25% replacement group. That is, replacing part of the soybean meal with FCSM did not affect the growth of growing pigs. performance, also significantly reduces feed costs and improves economic benefits. A large number of studies have proven that fermentation has the function of removing phenols, improving nutritional value, and reducing harmful substances such as ANF. At the same time, fermentation can produce a large number of probiotics and bioactive substances to promote intestinal health.

At present, research on the application of fermentation technology in animal production has achieved good results. However, microorganisms come from a wide range of sources and their detoxification mechanisms have not been fully elucidated. The development of green and efficient microbial fermentation sources and the optimization of fermentation production processes may be the key to future microbial detoxification technology. research focus.

3.2 Enzyme treatment

Enzymes are a type of protein with biocatalytic effects. Feed enzyme preparations can be divided into two categories according to their characteristics and functions: ① Exogenous digestive enzymes, including protease, lipase and amylase, have the function of promoting the digestion of nutrients and Absorption and other functions; ② Exogenous degradative enzymes, including cellulase, hemicellulase, pectinase, β-glucanase and phytase, etc. [43], can improve feed conversion rate and nutritional value, improve Animal production performance, eliminating ANF in feed and increasing the availability of miscellaneous meal.

Ao Xiang et al. used 50 kg growing and fattening pigs as the research object to study the addition of carbohydrate enzymes (α-galactosidase 105 000 U/g, protease 2 300 U/g, β-mannan) into the palm kernel meal diet. Enzyme 12 000 U/g) on pig growth performance, nutrient digestibility and meat quality. The results showed that compared with the no enzyme group, adding 1 kg/t carbohydrate enzyme significantly increased the feed-to-weight ratio of growing pigs and the The apparent digestibility of dry matter and total energy improved growth performance but had no significant impact on meat quality. The reason may be that carbohydrase degrades NSP in palm kernel meal, thus providing more energy.

Zhan Xiu’an et al. studied the application of canola meal and complex enzyme preparations in fattening pigs and found that compared with the control group, the group adding 0.03% complex enzyme preparation (cellulase 10 000 IU/g, xylanase 6 000 IU/g, mannanase 5 000 IU/g, protease 12 000 IU/g), the apparent digestibility of dry matter and total phosphorus in finishing pig diets increased by 3.49% and 32.53% respectively (P<0.05).

Zhan et al. also found that compared with the control group, adding 0.03% enzyme preparations (cellulase, xylanase, mannanase and protease) increased the serum free triiodothyronine level of growing pigs by 17.01%. The serum immunoglobulin IgG, IgM and complement C3 and C4 contents increased by 12.59%, 20.59%, 36.18% and 24.00% respectively (P<0.01). The reason was due to the enzyme degradation of NSP and sulfur-containing glucose in canola meal. Glycosides are related to ANF such as erucic acid. Due to the specificity of enzymes in substrate selection, the application effect of enzyme preparations is closely related to feed components, animal digestive physiological characteristics, etc. Therefore, the use of enzyme preparations should be based on factors such as feed composition, animal breed and age.

3.3 Extrusion and puffing

Extrusion puffing is a high-temperature, short-term processing process formed under the combined action of moisture, heat, mechanical energy, pressure and other factors. It can be divided into dry puffing and wet puffing. During the extrusion and puffing process of the material, starch can be smelted, protein can be denatured, ANF can be destroyed, and sterilization and detoxification can be achieved.

Ni Haiqiu et al. found that the FG content in cottonseed meal was reduced by 87.85% after extrusion and puffing treatment; adding 5%, 10% and 15% of puffed cottonseed meal to the diet of growing pigs significantly improved growth compared with adding untreated cottonseed meal. Total antioxidant capacity (T-AOC) of pigs; during the fattening period, adding 10%, 15% and 20% expanded cottonseed meal to the diet can significantly increase the immunoglobulin of fattening pigs compared with the untreated cottonseed meal group , triiodothyronine and tetraiodothyronine, indicating that extrusion and puffing treatment can significantly reduce the ANF content in cottonseed meal and significantly improve the immunity and growth performance of fattening pigs.

At the same time, Ni Haiqiu et al. studied the effect of extrusion processing on the ANF content in rapeseed meal and the effect of expanded rapeseed meal (ERSM) on the growth performance of growing and fattening pigs. They found that compared with rapeseed meal, ERSM crude fat and The dry matter content increased significantly, and the ANF content including thioglucoside and phytic acid decreased significantly; when the addition amount was 6%, the apparent digestibility of CP, crude fat and dry matter of growing pigs fed ERSM were all significant. significantly higher than those fed rapeseed meal. According to Table 6, it can be seen that extrusion puffing can reduce the ANF content in mixed meal, improve the palatability and nutritional value of feed, and improve the utilization rate of mixed meal. The reason may be that the high temperature, high pressure and expansion effect during the extrusion and puffing process destroy It breaks the structure of the plant, releases partially surrounded and bound digestible substances, and partially degrades the undigestible cellulose. Therefore, the rational use of extrusion and puffing technology can significantly improve the quality of mixed meal, and is an effective means to improve the quality and efficiency of mixed meal.

4 Summary and outlook

Mixed meal has great potential to replace soybean meal due to its high nutritional value, large yield, and low cost. At the same time, a series of application studies of mixed meal in animal production have fully confirmed its feasibility as a substitute for soybean meal. However, due to the wide variety and complex composition of mixed meal, there are still a series of problems in the production and application, such as anti-nutritional factors, amino acid balance, excessive mycotoxins, etc.

Therefore, in response to the above issues, future research is recommended to be carried out from the following aspects:

① Systematically optimize pre-treatment processes such as microbial fermentation, multi-enzyme compound hydrolysis and extrusion puffing to eliminate anti-nutritional factors of mixed meal, improve its palatability and nutrient digestibility, and improve the quality and efficiency of mixed meal;

② For different types of mixed meal, the appropriate dosage should be clarified at different growth stages of livestock and poultry, and standards should be established;

③ Clarify the changing rules of main nutrients during the pretreatment of mixed meal, and establish a precise processing technology system based on “pretreatment process parameters – anti-nutritional factors – nutrient availability – animal production performance”. By increasing the feed value and application ratio of miscellaneous meal, we can reduce production costs and achieve reduced substitution of soybean meal, thereby reducing dependence on imported soybeans and ultimately ensuring the sustainable development of my country’s livestock industry.