Mannos-oligosaccharides, as a kind of microbal ecological additive ,has become the focus the discussion in animal nutrition.This paper reviews the source of MOS ,physical and chemical characteristics,functional mechanism,applying effects and effected facts.Functional mechanism, Applying effects, Effected factors facts.

Since the discovery of tetracycline's growth-promoting effect on livestock and poultry in the 1940s, antibiotics have been widely used in the breeding industry as livestock and poultry growth promoters and antibacterial drugs, and have been effective in improving livestock and poultry productivity. However, studies in recent years have found that long-term use of antibiotics is prone to produce drug-resistant strains and residues in livestock products, and affect human health and damage the ecological environment through the food chain. Therefore, many countries have successively issued laws to prohibit or restrict the use of some antibiotics in feed, and then seek a low (or no) pollution, low (no) residue green feed additive. A large number of studies have shown that as a new type of microecological effect additive, manno-oligosaccharide, which has the dual functions of adsorbing intestinal pathogens and exerting immune regulation, thereby improving animal production performance. Therefore, it has been regarded as one of the most promising antibiotic substitutes.

1. Source of Manno-oligosaccharides

Manno-oligosaccharides (MOS) are phosphorylated glucomannan protein complexes extracted from yeast cell walls rich in manno-oligosaccharides by enzymatic hydrolysis. They are the common name for manno-oligosaccharides. They are widely found in konjac flour, guar gum, tianpu gum and the cell walls of various microorganisms (glucomannan oligosaccharides). Currently, commercial manno-oligosaccharides are mainly produced by enzymatic hydrolysis. A large number of studies have shown that manno-oligosaccharides from different sources have different structures. For example, the more studied konjac manno-oligosaccharides are composed of glucose and mannose residues with a molecular ratio of 1:1.5 through β-1-4 glycosidic bonds, and their side chains are connected by β-1,3 glycosidic bonds. The main chain of glucomannan oligosaccharides derived from yeast cell walls is mainly arranged in a highly branched pyranose residue chain. The main chain is connected by α-1,6 glycosylation keyboard connection, and the side chains are connected by α-1,2 and α-1,3 bonds.

2.1 Optimizing the microecological environment of animals and reducing gastrointestinal diseases

Studies have shown that manno-oligosaccharides can regulate the microecological environment of the gastrointestinal tract of animals, promote the growth and reproduction of beneficial bacteria, inhibit the adhesion and colonization of harmful bacteria on the intestinal wall, and maintain a normal digestive tract environment. According to the research results of Peter et al. (1998), manno-oligosaccharides can promote the growth of beneficial bacteria such as Bifidobacterium, Lactobacillus acidophilus, and Lactobacillus delbrücki, while they can play a good inhibitory role on pathogenic bacteria such as Salmonella, Salmonella typhimurium, Clostridium botulinum, and Clostridium putrefaciens. First of all, manno-oligosaccharides can It selectively promotes the proliferation of beneficial bacteria in the animal intestine, such as Bifidobacterium, so that it forms a microecological competitive advantage in the gastrointestinal tract, directly inhibiting the normal functions of exogenous bacteria and intestinal inherent spoilage flora in terms of barrier, nutrition and immunity. Manno-oligosaccharides can promote the growth and reproduction of beneficial bacteria and ensure beneficial health care for the host. This function is achieved by forming an intestinal flora with Bifidobacterium and Lactobacillus as dominant bacteria. Bifidobacterium and Lactobacillus are important dominant flora that maintain intestinal health through multiple functions, thus forming a microecological competitive advantage and promoting the proliferation of beneficial bacteria in animals. Secondly, manno-oligosaccharides can inhibit the adhesion and colonization of harmful bacteria. In the past, considerable evidence showed that when manno-oligosaccharides are present, Escherichia coli with mannose-type chitin no longer adsorbs on animal cells. In this way, manno-oligosaccharides can inhibit the adhesion and colonization of harmful bacteria to a certain extent, thereby reducing gastrointestinal diseases.

2.2 Regulating immune defense mechanisms and enhancing animal immunity

Manno-oligosaccharides have certain immunogenicity and can stimulate the body's immune response. They can also bind to the surface of certain toxins, viruses and fungal cells and act as adjuvants for these exogenous antigens, slowing down the absorption of antigens and increasing the titer of antigens, thereby enhancing the cellular and humoral immune responses of animals. Some experts pointed out that yeast cell walls have strong antigen activation properties, and this property is also one of the manifestations of the physiological functions of manno-oligosaccharides in animals. In addition, since special polysaccharides derived from microorganisms also have adjuvant effects when added to bacteria, adding an appropriate amount of manno-oligosaccharides can also significantly improve the antibody response ability, thereby enhancing the protective function of the vaccine. In addition to having adjuvant and antigen properties, manno-oligosaccharides can also stimulate the liver to secrete mannose-binding protein, thereby affecting the immune system. KE Newman's research showed that pigs supplemented with manno-oligosaccharides had increased levels of IL-2 and IFN-Γ. The above two substances are two interleukins released in the early stages of the immune response. This result shows that the addition of MOS to the diet can significantly improve the antibody response ability. It speeds up the immune system's response to pathogens. It is reported that both manno-oligosaccharides and p-glucan can speed up the recovery of the suppressed immune system of piglets, and can effectively reduce mortality and diarrhea rates.

2.3 Exerting diverse biological activities and absorbing mycotoxins

In recent years, there have been relatively few studies on the adsorption of mycotoxins by manno-oligosaccharides, and the mechanism of manno-oligosaccharides in this regard is still in the exploratory stage. Past studies have shown that yeast cell wall material is relatively stable to acid hydrolysis, and its fragments can pass through the stomach or abomasum intact. This ability to resist acid digestion accounts for its wide range of biological activity in different types of animals, and this characteristic is the diverse biological activity of complex carbohydrates. Devegowda et al. reported that studies on in vitro liquid culture media showed that the addition of yeast culture could degrade or bind up to 88% of Aspergillus B1. Trenholm found that manno-oligosaccharides can bind to zearalenone, which can be physically adsorbed or directly bound to mycotoxins without affecting other feed ingredients.

3 Application effects of manno-oligosaccharides

3.1 Application of manno-oligosaccharides in pig feed

3.1.1 Piglets are subject to nutritional stress and environmental stress caused by supplementation and weaning, and the balance of intestinal flora is easily destroyed, so they have been studied more. The experimental results show that manno-oligosaccharide has the dual functions of absorbing intestinal pathogens and regulating immunity in piglets. Canada (1993) reported that adding 1.8g/kg MOS to piglet feed had a significant effect, with daily weight gain reaching 13.54%. The experiment conducted by Maxcell et al. at the University of Arkansas in the United States showed that adding BIO-MOS to piglets from birth to 38 days old After that, its feed conversion rate was equivalent to that of piglets fed with growth-promoting copper sulfate. Dvorak (1998) confirmed that manno-oligosaccharides can increase the daily weight gain and feed conversion rate of piglets. The reason may be that it improves the immunity of piglets and inhibits the proliferation of pathogens in the gastrointestinal tract. According to the experimental results of Zhou Hongli et al. (2002), the addition of manno-oligosaccharides can significantly reduce the concentration of Escherichia coli in each intestinal segment of piglets, and the effect is better as the amount of addition increases. At the same time, the reduction in diarrhea rate also has this trend, indicating that there is a certain correlation between Escherichia coli and piglet diarrhea. As for the effect of manno-oligosaccharides on the proliferation of beneficial microorganisms, further research is needed.

3.1.2 A large number of studies on pigs, sows and boars have shown that the effects of manno-oligosaccharides on pigs, sows and boars are not obvious. Lynos (1995) reported that manno-oligosaccharides can increase the weight gain of pigs by 5% in the later stage, but have no effect on feed utilization. In 1988, foreign scholars conducted an experiment on the effects of manno-oligosaccharides and other oligosaccharides on the estrus of sows and found that they can shorten the estrus cycle by 9 days. In addition, long-term use in feed can increase the average number of piglets born by sows by 0.7 heads; increase the number of boar sperm by 20%-25%; and reduce constipation in sows before and after delivery. Sping (2000) reported that manno-oligosaccharides can enhance the immune response of pigs to infections such as Salmonella, hemolytic Escherichia coli and Campylobacter.

3.2 Application of mannan-oligosaccharides in chicken feed

3.2.1 Broiler

Ther mannan-oligosaccharides can increase the daily weight gain and feed conversion rate of broilers, thereby improving their economic benefits. According to Alltech (1994), the survival rate increased by an average of 0.4% when 0.2% mannan-oligosaccharides were added to chicken feed. Savage et al. reported in 1996 that the IgA level in the bile of broilers fed with mannan-oligosaccharides increased by 14.2%. Wang Quan (2002) showed through anatomical experiments on chickens that the addition of mannan-oligosaccharides at a rate of 25 g/kg to the feed had a significant stimulating effect on the bursa, thymus, and cecal tonsils. Compared with the control group, the weight of the bursa increased by 37.6%, and the weight of the thymus increased by 11.5%. The change in the percentage of T cells was dependent on the amount of mannan-oligosaccharides used. This shows that mannan-oligosaccharides can effectively promote the specific reproduction of T cells and increase the percentage of T cells.

3.2.2 Laying hens

The mannan-oligosaccharides also have a certain effect on egg components. According to Stanley (1996), the cholesterol level in the eggs of laying hens in the experimental group (fed with a diet without mannan-oligosaccharides) was reduced by 20.1% compared with the control group (fed with a diet without mannan-oligosaccharides).

3.2.3 Turkeys

Recent studies have shown that mannan-oligosaccharides have a significant effect on the growth performance and immune system of turkeys. According to Randy et al. (1995), when mannan-oligosaccharides were added to the turkey diet, the survival rate increased by 5.27% compared with the control group (without mannan-oligosaccharides), and the average body weight increased by 1.21%. Olsen also had a similar report in the same year. Savvage et al. (1996) concluded through experiments that mannan-oligosaccharides can increase the level of IgA in the turkey mucosa and significantly increase the amount of IgG in the turkey blood. The increase in both means that mannan-oligosaccharides can simultaneously enhance the immune response related to intestinal mucosal and humoral immunity.

3.3 Application of Manno-oligosaccharides in Cattle Feed

The effect of adding manno-oligosaccharides to cattle feed is mainly manifested in the adsorption of mycotoxin pathogens and the improvement of calf weight gain. Newsman et al. (1993) found that for Holstein bull calves fed with milk replacer, the addition of MOS can significantly increase the body weight at 35 days of age. The reason for the improvement in growth is that the incidence of bacterial pneumonia at 4-5 weeks of age decreased (70%-80% lower than the control group). Newsman (1995) also reported that manno-oligosaccharides can enhance immunity and reduce respiratory diseases in calves, thereby significantly increasing the daily weight gain of calves. Dilday et al. (1997) also reported that manno-oligosaccharides can significantly increase the daily weight gain of calves and reduce the incidence of morbidity.

3.4 The application of manno-oligosaccharide in aquatic animal feed

has proved that manno-oligosaccharide as an additive in aquatic animal feed can promote fish growth, reduce mortality, reduce the amount of nitrogen discharged in feces, and prevent pollution. Yoshida et al. reported that manno-oligosaccharide can significantly improve the cell activity and feed utilization efficiency of catfish. In the same year, a certain Scottish fishery college also reported that 0.1% manno-oligosaccharide was added to African catfish feed and aquatic Aeromonas aeruginosa was inoculated at the same time. After 12 and 24 hours of inoculation, the number of cells in the blood and spleen was checked respectively, and it was found that there was a significant decrease. Jiang Bo used 100 fish for experiments. The results showed that the experimental group (MOS group) gained 22.26% in weight and the feed efficiency increased by 7.56%. Other studies have shown that the mortality rate of squat fish fry when they are between 1 gram and 7 grams in weight after being attacked by cold water pathogens is as high as 25%. After adding 0.7% MOS to the bait, the mortality rate at this stage can be reduced to 1%. Manno-oligosaccharide can enhance the immunity of fish.

3.5 Application of manno-oligosaccharides in other animal feeds

Rosell (1991) reported that adding 0.2% manno-oligosaccharides to weaned rabbit feed reduced feed conversion by 15% and mortality by 3.6% at 35 days after weaning, and increased daily weight gain by 3 g/rabbit; Reid (1994) reported that adding 1%-2% manno-oligosaccharides to weaned rabbits under severe stress conditions could reduce mortality; Randy and Olsen (1994) showed that adding manno-oligosaccharides to commercial ostrich feed (0.91 g/kg in the first 3 weeks and 0.46 g/kg from 3 to 17 weeks) increased feed conversion by 5%, survival rate by 4.43%, and weight gain by 0.191 kg/rabbit compared with the control group (virginiamycin control group).

4. Factors affecting the effect of manno-oligosaccharides in feed

4.1 Animal species, age, and physiological state

Animal species, age, and physiological state are direct factors that affect the efficacy of manno-oligosaccharide use, but there are few reports on this. Shao Liangping et al. reported that manno-oligosaccharide can significantly increase the level of leukocyte differentiation antibody CD3 in suckling piglets (P<0.01), but has little or no effect on meat pigs or poultry.

4.2 Types, purity, polymerization degree, and physiological activity of manno-oligosaccharide

Due to the variety of monosaccharide connection methods and the complex structure of oligosaccharides, different types of manno-oligosaccharides have different purities and polymerization degrees. Even the same type of manno-oligosaccharides from different manufacturers and batches have different structures, and of course there are also different degrees of differences in biological activity and efficiency.

4.3 Mannan oligosaccharide addition amount and addition method

Mannan oligosaccharides must have a certain concentration to play a role in the proliferation, exclusion and immune functions of intestinal bacteria. If the addition amount is insufficient, it will not have a significant proliferation effect; if the addition amount is excessive, it will not only greatly increase the feed and breeding costs, but also fail to increase the reproduction of beneficial bacteria and may cause diarrhea in animals. It is generally recommended that the dosage for weaned piglets should not exceed 0.4%. The study by Brendemuhl and Harvey showed that 0.2% was better than 0.1%, but there was no significant difference. However, there are also inconsistent reports. Therefore, the issue of the amount of manno-oligosaccharide added still needs further discussion.

Long-term studies have shown that feeding manno-oligosaccharide to animals in a decreasing manner has a better effect, that is, the amount added is higher in the early stage and then gradually reduced. Cole and Stockland reported that the effect of adding BIO-MOS (0.4%, 0.2%, 0.1%) in a decreasing manner was better than the effect of adding 0.2% level throughout the whole period. Zhou Hongli et al.'s experiment showed that the daily weight gain of adding BIO-MOS in a decreasing manner increased by 12% compared with the control group and 9% compared with the 0.2% BIO-MOS group, which is consistent with previous studies. It is worth noting that excessive addition of MOS can cause excessive development of the hindgut segment, causing mild diarrhea in animals, affecting the absorption and utilization of nutrients by animals, and inhibiting the growth of animals.

4.4 There are few reports on the effects of mannan-oligosaccharides naturally present in feed on animal production performance. In fact, the composition of the diet can affect the absorption and utilization of nutrients by animals to a certain extent. Improper addition of mannan-oligosaccharides in the diet not only fails to promote growth, but may even harm the health of animals. Other studies have shown that the type of diet and the composition of animal feed can also affect the internal environment of the intestine, thereby ultimately affecting the effectiveness of mannan-oligosaccharides.

4.5 Feeding environment

Under good feeding conditions, the addition of oligosaccharides such as mannan-oligosaccharides to the diet may not have a significant effect. Like other types of additives such as organic acids, antibiotics, and probiotics, the effect of mannan-oligosaccharides on production performance also varies greatly with feeding conditions. Shi Baoming et al. have related reports that they can only show significant growth-promoting effects when the impact on production performance is greatly affected by intestinal factors.

4.6 Synergistic effect of manno-oligosaccharides with antibiotics and probiotics

People have found that while feed antibiotics effectively kill microorganisms and improve the economic benefits of animal husbandry, they also inhibit the normal symbiotic beneficial microorganisms in the animal body, destroy the balance of intestinal microecology, and make animals susceptible to double infection or endogenous infection. According to the mechanism of action of manno-oligosaccharides, if manno-oligosaccharides are used in combination with antibiotics and probiotics, can they achieve better synergistic effects? Many people have discussed this idea. For example, King (1993) used manno-oligosaccharides and antibiotics to study the weight gain and feed conversion of young boars and gilts and found that the combined use effect was better than the single use of antibiotics. Zhou Zhongkai et al. (1999) also reported on this. However, how to coordinate the relationship between the two and maximize the functions of both is still the direction of our future research.

5. Prospects for the application of manno-oligosaccharides

In the situation where the voice against antibiotics as growth promoters for livestock and poultry is growing, the research on antibiotic substitutes is becoming increasingly urgent. Many countries have taken manno-oligosaccharides as a major direction to replace antibiotics.

As a microecological effect additive, the domestic feed industry has also given manno-oligosaccharides a high evaluation. It overcomes the shortcomings of all previous antibiotics, probiotics, enzyme preparations, etc., with a small dosage, pure natural, no residual flow and strong stability, and can improve the disease resistance of animals, promote animal growth, and has a good application prospect in animal nutrition.