Research progress on the application of microbial fermented roughage in ruminant production

With the continuous development of animal husbandry, farmers and herdsmen have become more and more mature in their cognition and utilization of roughage. However, roughage has poor palatability and low digestibility. In order to improve the quality of roughage, improve palatability, digestibility and control the feed cost of aquaculture, the research and development of new low-cost roughage has attracted widespread attention. Microbial fermented roughage has gradually become a research hotspot because of its excellent palatability, low price and high feeding value.   
1. Types of roughage and recent utilization   
Roughage is the main source of nutrition for ruminants, usually accounting for 40% to 80% of the diet. Choosing high-quality roughage can directly affect the health and growth performance of animals. There are many kinds of domestic roughage, such as various types of straw feed, husk feed, hay, leaves and other forage forest products, and the quality of different types varies greatly. In the "National Grain-saving Animal Husbandry Development Plan (2011~2020)" formulated by the Ministry of Agriculture and Rural Affairs, it is planned to increase the use of non-grain feed resources such as forage, agricultural by-products, light industry by-products, and animal husbandry while reducing food consumption. It can improve the yield and quality of livestock products. In 2017, the sown area of green fodder in my country was 1874.14khm2. In 2018, the sown area of green fodder in China was 1970.69khm2. To reduce the consumption of grain, it is necessary to increase the promotion of roughage types in my country to improve the utilization of non-grain feed resources.  
2. Routine treatment of roughage   
In addition to energy, roughage contains extremely low nutrients such as protein and minerals. Because of the high cellulose content, its digestibility is lower than 10.5MJ/kgDM, the digestibility of organic matter is lower than 65%, and its palatability is poor. The popularization and utilization have a great influence. However, through effective pretreatment of roughage, its nutritional value, palatability, and transformation can be increased, thereby improving resource utilization. At present, physical processing, chemical processing and biological processing are generally used.  
2.1 Physical method   
Physical methods mainly include shearing, crushing, soaking, grinding, cooking, microwave treatment, etc. Among them, mechanical crushing methods such as shearing, crushing, and green grinding mainly increase the surface area of roughage, reduce the length and particle size of roughage, increase dry matter intake, speed up eating speed, and improve palatability. Heat treatment methods such as cooking and thermal spraying increase the contact area by destroying the lignin and cellulose components in the roughage with high energy while destroying the fiber structure. Microwave treatment improves the enzymatic hydrolysis rate of crude fiber by changing the crystallinity of cellulose, destroying the surface structure of the material and increasing the specific surface area. Peng Xiaopeng et al. used microwave liquefaction method to treat lignocellulose group. In addition to removing lignin and xylan, it also destroyed the biological anti-degradation barrier of cellulose, which improved the enzymatic conversion efficiency in the subsequent enzymatic saccharification treatment.   
2.2 Chemical method   
Chemical treatment methods include alkali treatment method, ammonia treatment method, potassium permanganate treatment method, acid treatment method, oxidant treatment method, compound chemical method, etc., mainly by hydrolyzing cellulose or destroying the bonds between components, and decomposing parts Hemicellulose, reducing the degree of polymerization and crystallinity of cellulose, and removing lignin.   
2.3 Biological method   
Biological methods are mainly divided into silage, yellow silage, micro-storage and microbial treatment. Silage is to cut green feed into short lengths, compact and seal it into silage cellars or silage bags to maintain an anaerobic environment, so that lactic acid bacteria can continue anaerobic fermentation to form an acidic environment, thereby inhibiting the reproduction of other microorganisms and achieving long-term preservation. The advantages of improving the production efficiency of ruminants and reducing the cost of feeding. The corn stalks with low moisture content are used as raw materials for yellow storage, and after adding appropriate amount of water and biological agents, they are compacted and sealed for storage. The anaerobic fermentation of microorganisms is also used to form an acidic environment, which plays a role in preserving the nutritional value of feed. Micro-storage refers to adding microbial active bacteria to corn stalks and fermenting them in a closed container to saccharify lignin, and then convert sugars into lactic acid and volatile fatty acids under organic acid fermentation, forming an acidic environment to inhibit the growth of other microorganisms. Microbial fermentation is the use of beneficial microorganisms to ferment agricultural and food processing by-products to prepare new feed materials. It has good palatability, low price, and relatively high nutritional value. It can maintain the balance of intestinal microorganisms in animals, improve immunity, and increase production. performance. This article only reviews the mechanism of microbial fermented roughage, production and storage, strain selection and application in ruminant production.  
3. The role of microbial fermentation   
3.1 Improve the palatability and nutritional value of roughage   
Microbial fermentation of roughage helps to improve flavor and color, and improve palatability. Straw fermented by three bacteria (white rot fungus, yeast, Trichoderma konii) turns yellow, while silage alfalfa with lactic acid bacteria and cellulase , the silage sensory scores of the German Agricultural Association were excellent, and the two groups of silage alfalfa both emitted a strong aroma. In terms of nutritional value, the roughage fermented by microorganisms has increased crude protein content, accelerated dry matter digestion rate, and reduced crude fiber content. Zheng et al. used Bacillus to ferment soybean meal and found that Bacillus can degrade anti-nutritional factors (ANFS) and change the microstructure of fermented soybean meal protein, improving the nutritional quality of fermented soybean meal.   
3.2 Promote rumen development and microbial colonization   
The energy and protein needed to maintain performance and health of ruminants is mainly dependent on the fermentation and growth of microorganisms in the rumen. The rumen environment interacts with the microorganisms in it. A suitable rumen environment is conducive to microbial colonization, and beneficial rumen microorganisms form a good rumen environment and promote the healthy development of the rumen. Improving the diet and optimizing the fine-to-grain ratio are the easiest means of regulation. Because concentrated feed can promote the differentiation and development of rumen papillae, roughage can promote rumen development and microbial colonization. Khonkhaeng et al. fed beef cattle fermented white rot fungi extracted and cultured from Pleurotus ostreatus and Straw mushroom, and found that after feeding for 4 hours, the bacteria in the rumen increased by 0.60×1010 and 0.15×1010cell/mL, and the protozoa decreased. 0.58×106, 1.00×106cell/mL, and the NH3-N content in the rumen increased by 1.76, 1.91mg/dL respectively. The reason may be that white rot fungi increased the activity of exogenous cell wall degrading enzymes by decomposing rice straw fibers, thereby increasing bacterial attachment, stimulating the richness of rumen microbial populations, and strengthening the synergistic effect with rumen microbial hydrolytic enzymes. And rumen NH3-N is the main product of protein digestion, which can be used by rumen microorganisms, and the increase of NH3-N content is conducive to microbial colonization. This result also verified the view that Khonkhaeng's roughage fermented by white rot fungus can increase the content of NH3-N in the rumen. Experiments have found that yeast cultures are rich in active polysaccharides, polypeptides, organic acids, various enzymes and growth-promoting factors and other nutritionally active substances that are conducive to bacterial colonization in the rumen, and yeast can improve the utilization of rumen bacteria on yeast cultures. rate, increase the number of bacterial colonization, and further benefit the development of the rumen. Therefore, feeding microbial fermented roughage is more conducive to rumen development, microbial colonization, and energy and protein synthesis.  
3.3 Inhibit harmful microorganisms and improve animal immunity
The inhibitory effect of microbial fermented roughage on harmful organisms is mainly manifested in the fact that beneficial bacteria compete with pathogenic bacteria for inhibition. Probiotics are bacteria species that, when administered in sufficient quantities, confer health benefits on the host. The most common probiotics include Lactobacillus, Bifidobacterium, Enterococcus, Faecalis coli, Clostridium, and Propionibacterium. Jiang Xin et al found that the feed fermented by Bacillus natto and Lactobacillus can significantly increase calf plasma IgA and IgG by 16.39% and 12.16% respectively compared with the control group.
4. Microbial fermented roughage strains
The State Council stipulates that the selection of feed additives must refer to the category catalog formulated and published by its subordinate agricultural administrative department. Currently, 35 microbial strains are allowed to be added to the feed. Adding probiotics (Lactobacillus salivarius, Bacillus subtilis and Saccharomyces cerevisiae) can increase the lactic acid content in the fermented feed, reduce the total volatile fatty acid content, and help preserve more nutrients. Enriched some potentially beneficial microorganisms and small molecule compounds with antibacterial activity, which may help to inhibit the growth of pathogens. Different strains have different improving effects. Some strains only improve the nutrient content of roughage and have a positive effect on reducing ANFs (anti-nutritional factors). Some strains only have a positive effect on improving intestinal enzyme activity, while others can simultaneously Improve these two aspects. For example, Bacillus can degrade anti-nutritional factors; feed fermented by Lactobacillus plantarum can improve intestinal enzyme activity and thus improve digestibility; yeast can improve the activity of certain microorganisms in the rumen of dairy cows, thereby improving lactation performance and reducing the risk of feeding high-starch diets. Risk of subacute ruminal acidosis due to grain changes when feeding dairy cows. In addition to using a single strain, the mixed use of two to three strains has gradually become a development trend. Wang Wei et al. found that the degradative effect of mixed strains of corn stalks was significantly higher than that of single strains.
5. Production and storage of microbial fermented roughage
5.1 Microbial Fermentation Roughage Production
The production of microbial fermented roughage is mainly divided into liquid fermentation and solid state fermentation. Liquid fermentation means that after mixing roughage and water at a ratio of 1:1.5 to 1:4, the feed is fully fermented to form a stable state through the metabolic activities of microorganisms in the fermentation broth. Liquid fermented feed is widely used in pig production, but there are few reports on ruminants. Solid-state fermentation refers to that when microorganisms ferment in a solid medium that is insoluble in water but has a certain humidity, they continuously absorb the water in the solid medium matrix particles, and gradually develop solid-state fermentation to viscous fermentation and solid fermentation through the flow of water during the absorption process. Particle suspension fermentation. Compared with liquid fermentation, solid-state fermentation is closer to natural fermentation. Yeast was used to prepare solid-state fermented feed, and the contents of crude protein, total phenols, vitamin B2 and low-molecular-weight peptides were significantly increased after fermentation.
5.2 Storage methods of microbial fermented roughage
The storage method of fermented roughage determines its service life. Sun Guoli's test results show that there are significant differences in pH value, crude protein, crude ash and soluble carbohydrate content of corn silage made by two different storage methods: barreled and bagged. .
6. Application of microbial fermented roughage in ruminant production
6.1 Effects of microbial fermented roughage on growth performance of ruminants
The main indicators of ruminant growth performance are feed intake, daily gain, feed-to-weight ratio, and nutrient digestibility. Yuxia's research found that the average daily gain (PPPPPP>0.05) of mutton sheep fed corn stalk fermented feed was higher than that of the control group, but the difference was not significant. Qiu Yulang et al. found that the average daily gain of mutton sheep increased by 36% compared with the unfermented straw and corn steep liquor mixed feed with microbial fermented straw and corn steep liquor.
6.2 Effects of microbial fermented roughage on the quality of ruminant products
In ruminant production, meat quality and milk production are core indicators. Studies by Wang Limei and others have shown that feeding fermented feed with potato dregs can significantly
7. Outlook
Microbial fermentation of roughage has the advantages of improving roughage crude fiber structure, reducing anti-nutritional factors, increasing feed intake and digestibility of ruminants, and improving immunity, etc., and has broad prospects in ruminant production. At present, the research on the specific mechanism of action of bacteria in fermented roughage is not completely clear, and the research on the selection of single strains, the combination mechanism and ratio of mixed bacteria, and the type of roughage is not complete enough. Microbial fermented roughage can significantly improve the production performance of ruminants, but in terms of ruminant product quality, although it has the effect of improving meat quality, it is not significant, and there is no significant improvement in milk quality. Therefore, carrying out related research work on strains, animal immunity, intestinal flora, and nutrient metabolism will be of great help in understanding the mechanism of microbial fermented roughage and developing fermented feeds for different strains, roughages, and animal species in accordance with local conditions. Significance. Article source: Biological Feed Engineering Research Center