DDC Science and Technology Day | Microbial Fermented Feed and Its Application
ABSTRACT: This paper summarizes the production of microbial feed by fermentation engineering fermented meal, straw and fruit residue, which improves the utilization rate of feed, improves feed quality, eliminates environmental pollution, alleviates the shortage of protein feed raw materials in China, as well as the application of microbial fermented feed in animals, and puts forward the problems and development prospects of fermented feed.
Key words: fermentation engineering; meal raw materials; fruit residue; microbial fermentation feed
Fermentation engineering, also known as microbial engineering, refers to the use of modern engineering technology means, using some specific functions of microorganisms, to produce useful products for human beings, or directly apply microorganisms to industrial production process. The main body of fermentation engineering is microorganisms, especially those modified by DNA recombination. At present, the application of fermentation engineering in feed and animal husbandry has achieved good results. In recent years, the price of feed raw materials has been rising continuously, and the cost of livestock and poultry breeding has been greatly increased, which has seriously affected the development of animal husbandry and feed industry in China. Therefore, improving feed utilization ratio and feed quality is one of the research focuses in feed industry. This paper mainly summarizes the application of fermentation engineering in feed raw materials.
1 Microbial Fermentation 
Eliminating anti-nutritional factors, accumulating beneficial metabolites, improving feed utilization and animal digestibility, mainly include: soybean meal. Protein feedstuffs such as cotton meal, rapeseed meal and peanut meal degrade their anti-nutrient factors, such as antigen protein of soybean meal, gossypol of cotton meal and thioglycoside of rapeseed meal, and digest protein in vitro. Fermentation can change the physical and chemical properties of meal raw materials, reduce anti-nutrient factors, produce beneficial ingredients for animal growth, improve digestibility of feed, increase palatability and prolong storage. It can also detoxify and detoxify, transform toxic meal into non-toxic and low-toxic high-quality feed, improve the utilization rate of nitrogen, reduce nitrogen pollution in feces, reduce livestock environmental pollution, accumulate beneficial metabolites such as small peptides and lactic acid, inhibit the growth of pathogenic microorganisms, greatly reduce or completely replace the use of antibiotics; non-sediment of feed materials such as barley, straw, etc. In vitro digestion of powder polysaccharide makes it easy for animals to digest and absorb, and improves the metabolic ability and palatability of feed .
2 Fermented feed raw materials
2.1 Fermented Meal Raw Materials
Soybean meal is a by-product of soybean oil extraction. It contains abundant protein and amino acid. It is a common plant protein raw material in animal feed. Ma Wenqiang et al.  After soybean meal was fermented by Bacillus subtilis, Saccharomyces cerevisiae and lactic acid bacteria, crude protein increased by 13.48%, crude fat increased by 18.18%, phosphorus content increased by 55.56%, amino acid increased by 11.49%, trypsin inhibitor and other anti-nutritional factors were eliminated completely. Mozhongwen et al.  fermented soybean meal with mixed strains of Aspergillus oryzae and Saccharomyces cerevisiae, which increased the crude protein content by 12.1%. Yang Xu  et al. used Saccharomyces cerevisiae to solid-state ferment soybean meal, which increased the protein content by 9.55%.
Cotton meal is a kind of high quality vegetable protein feed with high amino acid content and crude protein content second only to soybean meal. However, free gossypol has a certain toxic effect on animals, which limits its use in feed. In recent years, cottonseed meal has been fermented to reduce the content of free gossypol, improve the utilization rate of protein and improve the quality of cottonseed meal, which has broad application prospects. Zhuge Bin et al.  fermented cottonseed meal by mixed bacteria increased the content of small peptide to 18.36% and the digestibility in vitro to 88.59%, which significantly increased the protein content of cottonseed meal. Qiao Xiaoyan et al.  After cottonseed meal was fermented by Candida tropicalis and Lactobacillus casei, gossypol detoxification rate reached 48.1%, small peptide content increased by 10.97%, amino acid increased by 10.81%, phytic acid decreased by 1.54%. Nieber  fermented cottonseed meal with Bacillus cereus, protein increased by 3.79%, free gossypol detoxification rate 53.4%. Golden Red Spring  fermented cottonseed meal to remove free gossypol. The rate was 96.52%.
Rapeseed meal contains antinutritional factors such as glucosinolate, erucic acid, tannin, phytic acid and sinapine, which severely limits its application in feed. Therefore, detoxification of rapeseed meal by fermentation has been widely nourished. Wang Gang  made the degradation rate of glucosinolate 53.4%, crude protein 5.58%, rapeseed peptide 8.1% and protein digestibility 1.94% by mixed solid-state fermentation of rapeseed meal; Lu Yu  made the removal rate of glucosinolate 97% by mixed solid-state fermentation; Sun Lin  made solid-state fermentation by lactic acid bacteria, Bacillus subtilis, Bacillus cereus, Clostridium butyricum. The removal rate of glucosinolate from rapeseed meal was 85.19% and the crude protein content was increased by 4.37%.
China is a large agricultural country, with abundant crop straw resources. About 65% - 80% of the dry matter in the straw can provide energy for animals. At present, less than 10% of the straw is used as feed. Most of the straw is directly returned to the field or used as fuel, which causes a great waste of resources and further pollutes the environment . Therefore, it is of great practical significance to treat straw as feed by fermentation. The lignin degradation rate and cellulose degradation rate were 44.77% and 41.48% respectively when mixed bacteria were used to ferment straw. Li Riqiang et al.  increased the true protein content of corn straw by 129.6% and the crude protein content by 29.59% through solid-state fermentation. After fermentation, the degradation rate of straw cellulose was 38.5%, 28.2%, hemicellulose 13.7%, 27.5%, protein content 15.43%, 12.32% higher than that before fermentation.
2.2 fruit residue
As a big agricultural country, every year