Research Progress on the Application of Functional Feed Additives for Intestinal Protection in Laying Hens

This article has been published in China Feed Additives, Issue 1, 2021, and the full text is as follows:

Protection of intestinal functional feed additives

Research Progress of Application in Laying Hens

Liu Wei Liu Xiaohui Liao Yuxue Xie Qingzhu

Anchi (Shandong) Animal Nutrition Research Institute Co., Ltd., Jinan Shandong 250013]]

Abstract:With the continuous extension of the breeding cycle of laying hens, the production performance and egg quality of laying hens have been seriously challenged. After the feed "ban", the use of functional feed additives to protect the intestinal tract is becoming more and more common. How to screen effective functional additives is very important for the healthy breeding production of laying hens. In this paper, the application of enzyme preparation, probiotics, plant essential oil and acidifier in improving the intestinal health of laying hens in recent years was reviewed.

Key words:Laying hens, intestinal health, enzyme preparation, probiotics, plant essential oil, acidifier

In recent years, the breeding cycle of laying hens has been extended, and the market is generally more than good.500Day. Laying hens enter the late stage of laying after high-intensity metabolism at the peak of laying, the body gradually ages, production performance and egg quality decline rapidly, and metabolic diseases such as fatty liver and osteoporosis are highlighted and intensified (Zhou Jianmin et al,2019). One of the important reasons for this is that the intestinal health status of laying hens decreases rapidly with the extension of the breeding cycle. The intestinal tract is not only the digestive organ of animals to digest and absorb nutrients, but also the immune organ to protect the health of the body. The intestinal tract protects the body from harmful exogenous microorganisms through the physical barrier formed by intestinal epithelial cells, the chemical barrier formed by digestive juices, digestive enzymes and other substances, the microbial barrier formed by intestinal microbial flora and the immune barrier formed by the intestinal immune system. Therefore, intestinal health is an important basis for the health of laying hens, the normal laying performance and the quality of eggs.

The materials used in the family farms of laying hens in China are mainly self-mixed with corn, soybean meal, bran, stone powder and premix. Under the premise of ensuring the quality control of large raw materials such as corn and soybean meal, the quality of premix determines the production performance and egg quality of laying hens. The premix mainly provides animals with calcium, phosphorus, sodium and other major elements, iron, zinc, copper, manganese, selenium, iodine and other trace elements, fat-soluble and water-soluble vitamins, and some basic nutrients such as limiting amino acids. The source form of these nutrients, the amount of use and the proportion balance between different elements are essential to ensure the normal production performance of animals. In addition, the use of functional feed additives is an important factor to reflect the quality of premix products. For a long time, feed antibiotics have been used as one of the cheapest and most effective solutions to solve the intestinal problems of livestock and poultry. From2020Year7Month1After the prohibition of daily feeding antibiotics, green and safe feed additives with the function of protecting intestinal health have become an important choice to replace antibiotics. In this paper, the application of enzymes, probiotics, plant essential oils and acidifiers in improving the intestinal health of laying hens was reviewed.

1. enzyme preparation

According to the different ways of improving the intestinal health of livestock and poultry, enzyme preparations can be divided into two main categories. The main functions of the first type of enzyme preparation are to reduce the anti-nutritional factors in feed, improve the digestion and absorption rate of feed, reduce the excretion of undigested nutrients such as protein, carbohydrate, calcium and phosphorus with feces, and reduce the production of harmful substances such as ammonia, urea and indole by intestinal fermentation of undigested organic nutrients (BedfordandSchulze,1998), thereby reducing the burden of intestinal digestion and reducing the damage of anti-nutritional factors to the intestinal tract, such as phytase, protease,Beta-mannanaseNon-starch polysaccharide enzymes, etc. The second category is able to indirectly or directly sterilize and regulate the balance of intestinal flora, such as glucose oxidase and lysozyme. In recent years, scientific research and production have paid more attentionBeta-Mannanase and glucose oxidase.

1.1 Beta-mannanase

The feed formula structure used in China's aquaculture industry is based on corn.-Soybean meal type mainly. Although soybean meal is a high-quality plant-derived protein material, it also contains many anti-nutritional factors. In addition to the traditional trypsin inhibitor, glycinin andBeta-Proteins such as conglycinin are anti-nutritional factors, and soybean meal also contains some carbohydrate anti-nutritional factors, suchBeta-Mannan, about in soybean meal1.3%（Dierick, 1989）。Beta-Mannans are part of the hemicelluloses of legume cell walls, producedD-mannoseβ-1,4A homopolysaccharide formed by glycosidic linkage. Monogastric animal intestines can secrete the ability to hydrolyzeAlpha -1,4Glycosidic bond homopolymeric polysaccharides (such as starch) are digestive enzymes, but cannot be secreted for hydrolysisβ-1,4Digestive enzymes for glycosidic bonds. Therefore, the undigestedBeta-Mannan adversely affects monogastric animals.Beta-The anti-nutritional effects of mannan are mainly manifested in two aspects. First, like traditional non-starch polysaccharides,Beta-Mannan is dissolved in water in the intestine of monogastric animals to form a gel, which increases the viscosity of digestive tract chyme, reduces the contact between chyme and digestive enzymes, and reduces the digestion and absorption rate of nutrients (Li Fuwei et al,2007); The fermentation of undigested nutrients in the intestine is conducive to the growth of harmful microorganisms and affects intestinal health.Wuetc (2005) Studies have reported that mannan has the ability to increase the viscosity of animal digestive tract chyme and affectIGF-1The secretion of insulin and glucagon, inhibit the absorption of blood sugar and other anti-nutritional effects. Second, the feed.Beta-mannanIt is a typical pathogen-related molecular pattern in molecular immunology, which can be recognized by the specific receptors of the intestinal immune system, trigger the corresponding immune response, and aggravate inflammation (SteelWait,1998）。Beta-Mannanase is an endonuclease produced by the fermentation of Bacillus sp., which can freely cleave between galactomannan, galactoglucomannan and mannanβ-1,4Glycosidic bond.Wuetc (2005) studies have shown that the additionBeta-Mannanase can improve the performance of laying hens and corn-Energy utilization of soybean meal type diets.Leeetc (2013) and other studies have shown that,Beta-mannanaseIt can improve the production performance of laying hens in the late stage of laying.Ryuetc (2017) and other studies pointed out that regardless of the content of mannan in the diet,Beta-Mannanase has a positive effect on the production performance and nutrient digestibility of laying hens.

1. 2. glucose oxidase

Glucose Oxidase State Ministry of Agriculture and Rural Affairs1999New feed additives identified in the year. Glucose oxidase is an aerobic dehydrogenase that catalyzes the reaction of glucose and oxygen in the gastrointestinal tract of animals to produce gluconic acid and hydrogen peroxide (MaurizioWait,1995). The reaction consumes oxygen to form an anaerobic environment in the intestinal tract, which can promote the growth and reproduction of anaerobic beneficial microorganisms such as Lactobacillus and Bifidobacterium in the intestinal tract. The hydrogen peroxide produced by the reaction can inhibit harmful microorganisms such as mold, Escherichia coli and Salmonella, thus regulating the structure of intestinal flora (Zhang Xiaoyun, 2006); The gluconic acid produced by this reaction can reduce the intestinalpHThe acidic environment is conducive to the digestive enzymes in the intestine to maintain activity and promote the digestion and absorption of nutrients (Marco et al,2009). Therefore, glucose can improve the intestinal health of animals from many angles. In addition, glucose oxidase also has a certain antioxidant effect. Wang Qanguang et al (2020) Studies have shown that the addition of glucose oxidase to the diet can increase the content of serum glutathione peroxidase and reduce the content of serum malondialdehyde in test ducks, indicating that glucose oxidase can oxidize glucose by consuming molecular oxygen or atomic oxygen in animals, showing the effect of enhancing the antioxidant capacity of the body. Song Haibin et al (2008) It was also found that glucose oxidase increased the activity of serum glutathione peroxidase in broilers to varying degrees, reduced the content of serum malondialdehyde, and had certain antioxidant and anti-stress effects.

2. Probiotics

Probiotics is a general term for a class of active microorganisms that are beneficial to the host. The common function of probiotics is to promote the growth of beneficial bacteria in the intestinal tract, inhibit the growth of harmful bacteria such as Escherichia coli and Salmonella, and protect the microecological balance of the intestinal tract. In addition, some metabolites of probiotics also have certain probiotic functions. At present, the probiotic additives commonly used in commercial feed are mainly lactic acid bacteria, Bacillus and Clostridium butyricum.3Class.

2.1lactic acid bacteria

Lactic acid bacteria are a class of gram-positive bacteria that can use fermentable carbohydrates to produce lactic acid (GosalbesWait,2000). The Ministry of Agriculture and Rural Affairs of China announced that the microbial feed additives allowed to be used are34species, of which there are22species belonging to lactic acid bacteria. The U.S. Food and Drug Administration has approved the microorganisms that can be used in feed.42species, of which there are30species belonging to lactic acid bacteria. Lactic acid bacteria inhibit the growth and reproduction of pathogenic bacteria by competing with pathogenic bacteria for nutrients in the intestinal tract of animals. At the same time, lactic acid bacteria also compete with pathogenic bacteria for the colonization site of intestinal epithelial cells to competitively reject the adhesion and colonization of harmful bacteria on intestinal epithelial cells, which plays a role in improving the balance of intestinal flora (Qiao Shiyan, et al,2014). The temperature resistance, acid resistance and bile salt resistance of lactic acid bacteria are poor, high temperature granulation, gastrointestinal lowpHOr high salt environment is easy to destroy the cell membrane of lactic acid bacteria to its death and loss of activity. Therefore, feed lactic acid bacteria additive products are mostly made into microcapsules or treated by embedding, coating and other technologies to improve the ability to resist gastrointestinal digestive juice and ensure that live lactic acid bacteria enter the intestinal tract to play a probiotic function. Affected by factors such as different strains and different coating technologies, the application effects of different feed lactic acid bacteria products in livestock and poultry production in the market are quite different, and the price of the products is also very different. The market price of lactic acid bacteria additive products with excellent performance is relatively high.

At present, the commonly used feed lactic acid bacteria additives mainly include Enterococcus faecium and Enterococcus faecalis treated by coating technology. These two kinds of bacteria belong to the strains with relatively good resistance in lactic acid bacteria, and their tolerance can be further improved by coating treatment.Tarasetc (2007) andSimon（2010) have confirmed that microencapsulated Enterococcus faecium can be colonized in the stomach, jejunum and colon of pigs, and can also be detected in feces.Wuetc (2018;2019) andYuanetc (2018) Enterococcus faecium can enhance intestinal mucosal barrier function, regulate intestinal flora balance and enhance intestinal mucosal immune response, and alleviate intestinal injury induced by Clostridium perfringens. Cao Guangtian et al (2018) The study found that the addition of Enterococcus faecium in the diet could significantly improve the growth performance of E. coli infected broilers, improve the immune-related index and improve the diversity of cecal flora. Guan Jingshu and Han Xia (2013) studies have shown that the addition250mg/kgEnterococcus faecium can improve the production performance of laying hens in the late stage of laying. Liu Song et al (2017) Studies have shown that the addition of Enterococcus faecalis to the diet of laying hens can improve the Hough unit, albumen height and yolk color of laying hens, reduce the total cholesterol content of serum and yolk, and regulate the number of intestinal microorganisms.

2.2bacillus

Bacillus is a kind of common bacteria in nature. The spores produced by Bacillus can survive in a variety of extreme environments and have strong stress resistance (Abbas,2019). Commonly used feed Bacillus additives are Bacillus subtilis and Bacillus licheniformis. Bacillus subtilis and Bacillus licheniformis are a kind of Bacillus, aerobic type, gram positive, with high temperature resistance, gastric acid resistance characteristics, can withstand high temperature granulation, not easy to be affected by various enzymes in the gastrointestinal tract, can effectively colonize the intestinal tract, consume intestinal oxygen to form an anaerobic environment, promote the growth of beneficial anaerobic bacteria, inhibit the growth of aerobic harmful bacteria, and maintain the balance of intestinal flora, at the same time, it can secrete protease, lipase and amylase and other digestive enzymes (RozsWait,2001), promote the digestion and absorption of nutrients, activate humoral immunity, improve immune function, and improve animal health (LeiWait,2013）。Leietc (2013) Studies have shown that adding Bacillus licheniformis to the diet of laying hens can increase egg production, increase eggshell thickness and eggshell strength, increase intestinal villus height, reduce crypt depth, and improve intestinal health.Chenetc (2020) and other studies have found that Bacillus subtilis can enhance the antioxidant capacity and intestinal immune barrier function of laying hens, and help to improve the laying performance of laying hens.Guoetc (2018) and other bioinformatics analysis showed that the up-regulated genes caused by the addition of Bacillus subtilis were involved in the peroxisome proliferator-activated receptor signaling pathway, starch and sucrose metabolism pathway, glycine/Serine/The metabolic pathway of threonine and galactose to promote nutrient absorption provides a new understanding of the probiotic mechanism of Bacillus subtilis on laying hens.

2.3Clostridium butyricum

Clostridium butyricum belongs to the genus Clostridium phylloides and belongs to obligate anaerobic Bacillus in biological classification. The bacteria can produce spores and have strong stress resistance. It has good characteristics of high temperature resistance, acid resistance and bile salt resistance. It has good resistance to high temperature and pressure granulation and digestive tract environment in feed processing process and has long residence time in animal intestinal tract (Kongqing, 2006). Like other probiotics, Clostridium butyricum can also promote the growth of beneficial bacteria in the intestinal tract, inhibit the growth of harmful bacteria, and protect the microecological balance in the intestinal tract. In addition, the special function of Clostridium butyricum is to produce small molecular metabolites such as acetic acid, butyric acid and lactic acid in the intestinal tract of livestock and poultry (Zheng Aijuan et al,2019), among which butyric acid is the main energy supply substance of intestinal epithelial cells, which provides energy for the proliferation of epithelial cells, and plays an important role in the repair and regeneration of intestinal epithelial tissues (Zhao Minmeng et al,2018). In addition, Clostridium butyricum can also improve intestinal immune function by inducing the expression of inflammatory factors and anti-inflammatory factors in intestinal epithelial cells (Wang Tenghao,2015), can enhance the activity of glutathione S-transferase in the intestinal mucosa and increase the content of glutathione, reduce the content of malondialdehyde, and improve the antioxidant performance of the animal intestine (Liao Xiudong,2015). Therefore, Clostridium butyricum plays an important role in maintaining the integrity of intestinal epithelial cells and intestinal health in laying hens.Zhanetc (2018) and other studies found that the addition of Clostridium butyricum in the diet can improve the immune function of laying hens in the late laying period, enhance the antioxidant capacity, improve the structure of the caecum flora, and improve the production performance and egg quality of laying hens in the late laying period.Wangetc (2020) Studies have shown that Clostridium butyricum can improve the intestinal absorption function of laying hens in the late laying period, and improve the efficiency of feed utilization and egg yolk color of laying hens in the late laying period.

3. Plant Essential Oils

Plant essential oils are aromatic molecules secreted by plant roots, stems, leaves, flowers, seeds, fruits or bark. They contain terpenes, alcohols, phenols, aldehydes, ketones, esters and other complex hydrocarbons (Yolk, 2020). The main components of plant essential oils are4Class. The first category is terpene compounds, such as alexol and geraniol; the second category is aromatic compounds, such as thymol and carvacrol; the third category is aliphatic compounds, such as isovaleraldehyde and linalool; The fourth category is nitrogen-containing and sulfur-containing compounds, such as allicin in garlic and trisulfide in onions (Feng Dongliang, etc,2018）。

Plant essential oils can degrade the cell wall of bacteria and destroy the protein structure of cell membrane, which is very important for Salmonella, Escherichia coli, Staphylococcus aureus, Campylobacter, etc.20This kind of pathogenicity has a strong antibacterial effect (CrandallWait,2015). Plant essential oils contain a variety of antioxidant active ingredients, with a certain antioxidant function, the specific mechanisms include: phenolic components combined with peroxy free radicals, reduce or will scavenge the activity of oxygen free radicals; phenolic hydroxyl andFe² andCu² and other metal ions chelate, block the biological oxidation process, reduce the generation of free radicals induced by metal ions; terpene chemicals improve the activity of antioxidant enzymes in the body and promote their antioxidant activity (Feng Dongliang,2018). Good antioxidant function can alleviate the degree of oxidative damage to the intestinal tract, oviduct and body of laying hens, and help laying hens to maintain stable laying performance and better egg quality in the later stage of laying. Plant essential oils can improve the intestinal health of livestock and poultry, enhance intestinal absorption capacity, and improve animal immunity (MourWait,2006）。Mitschetc (2004) Studies have shown that a mixture of plant essential oils (thymol and carvacrol) can inhibit the colonization and proliferation of Clostridium perfringens in the intestinal tract of broilers and help prevent the occurrence of necrotic enteritis. Zhang Wenjing (2007) and other studies have shown that plant essential oils can improve the production performance of livestock and poultry and improve immune function by improving the body's antioxidant activity, inhibiting intestinal harmful bacteria and stimulating appetite. Yang Jianping et al (2020) Studies have shown that adding150 mg/kgCompound Plant Essential Oils(Essential oil of star anise and thyme)be able to improve58The production performance of week-old Hailan brown laying hens can deepen the color of egg yolk, improve the relative abundance of Bacteroides phylum cecum, reduce the relative abundance of thick wall bacteria phylum cecum and Fusobacterium phylum, and improve the structure of cecum intestinal flora.Abdel-Warethetc (2016) Studies have shown that adding thymol to feed can improve24 ~ 36Egg weight, egg production, feed conversion and eggshell quality of week-old laying hens.Wangetc (2020) The study found that adding essential oil-rich mint leaves to the feed can improve64-76Laying rate, feed conversion rate and eggshell quality of late laying hens at week age.

4. Acidifying agent

Feed acidifier is an environmentally friendly green additive with no residue, no drug resistance and no toxic effects. China's Ministry of Agriculture and Rural Affairs issued the "Feed Additive Variety Catalog (2013) "is allowed to use more types of acidifiers, mainly organic acidifiers and organic acid salts, including formic acid, ammonium formate, potassium diformate, acetic acid, sodium diacetate, propionic acid, ammonium propionate, lactic acid, benzoic acid, sorbic acid, malic acid, tartaric acid, fumaric acid and citric acid, etc. The research and application of acidifier is mainly in the weaned piglet stage, which is used to reduce the acid force of feed system, reduce and stabilize the intestinal tract.pH, inhibit the reproduction of harmful intestinal bacteria, promote the digestion of nutrients in the diet, improve the activity of intestinal digestive enzymes and other biological effects (He Rongxiang, etc,2020）。

In the production of laying hens, water-soluble acidifiers can be used for drinking water, and can also be used to clean drinking water lines regularly, which can not only improve drinking water hygiene, but also improve intestinal health. Zhou Ling et al (2016) The study found that the compound acidifier composed of formic acid, lactic acid, propionic acid, butyric acid and lactic acid can improve the antioxidant capacity and immunity of laying hens, reduce the rate of dirty eggs, and reduce the salmonella infection of the body and eggs. Yang Jianping et al (2020) and other studies found that adding benzoic acid to the diet of laying hens can reduce the rate of broken eggs and the incidence of dark spots. Liu Yanli et al (2015) The study found that the addition of acidifiers (butyric acid glyceride, clove oil, cinnamon oil and oregano oil) in the feed of laying hens can improve the activity of amylase and trypsin in the intestinal tract of laying hens, reduce the number of Escherichia coli in the digestive tract, and improve the feed conversion efficiency and egg quality of laying hens.Gongetc (2020) The study showed that the addition of benzoic acid in the diet had no effect on the laying performance of laying hens, but it could significantly improve the egg quality, improve the intestinal morphology and structure, enrich the intestinal microbial composition, and have a positive regulatory effect on intestinal health.Yangetc (2019) and other studies have found that the combination of organic acids and essential oils (sorbic acid, fumaric acid and thymol) can increase the height of intestinal villi in laying hens, and can improve the digestive absorption capacity and barrier function of the intestinal tract by increasing the expression of intestinal nutrient transporters.

At the feed end“Forbidden resistance”, the breeding end is strict“limited resistance”As well as the increasing demand for safe and high-quality livestock products, feed companies need to continuously upgrade the formulation technology within a controllable cost. Therefore, the new green feed additives for the sustainable development of aquaculture will play an increasingly important role. However, there is still a big gap between single feed additive and feed antibiotics in terms of antibacterial effect and improvement of livestock and poultry production performance, and the combination of different types of additives has become a new trend. At present, there are many kinds of feed additives in the market, and the types, sources, combination methods, formula structure and processing technology of different additives will affect their use effect. And the cost of the formulation of additives is much higher than that of antibiotics. Therefore, the evaluation of functional additives by feed enterprises with strong R & D strength and large-scale animal experimental field will be more strict and scientific, and the effect of the combination of additives will be clearer. In the future, the R & D strength of feed enterprises will play an increasingly important role in improving product quality and promoting enterprise development.

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