Animal gut is both the main room, digest and absorb nutrients is also a important immune barrier, there are a lot of microbial flora, both to ensure the body health beneficial bacteria, also have damage to the body health of pathogenic bacteria, say usually beneficial bacteria mainly including bifidobacteria, lactobacillus and enterococcus, this kind of bacteria of intestinal more than 90% of the total number of bacteria, Intestinal harmful bacteria generally include escherichia coli and salmonella, the proportion is relatively small, but the impact on the animal body is also very large. Under normal circumstances, beneficial bacteria and pathogenic bacteria in the gut are in a dynamic balance. When the organism appears pathological, pathogenic bacteria multiply in large numbers and beneficial bacteria die gradually. The intestinal morphology and microflora balance are two important indicators to measure intestinal function.
Table 1: Diameters of bacteriostatic circles of plant extracts from different sources(mm)17
1.1 Bacteriostasis
Plant extracts have extensive antibacterial activity. So far, there are many reports on the antibacterial activity of plant extracts in vitro. Table 1 lists the inhibitory effects of 24 plant extracts on Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa. In vitro antimicrobial tests showed that extracts from tea tree, coriander, marjoram and pullorum had strong inhibitory effects on Escherichia coli, Salmonella and Staphylococcus aureus. The alkaloids extracted from the roots, stems and leaves of Celandine had inhibitory effects on Bacillus subtilis and Escherichia coli, while the total saponins extracted from the roots of Pulsatilla pulsatilla had inhibitory effects on Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Paratyphi, but the inhibitory effects were weak at low concentrations. Chinese bulbul saponins B4 can also inhibit escherichia coli, colorless, bacillus, verdigris false unit cell coli and klebsiella pneumonia bacteria growth, and from bergamot, lemon and orange extract linalyl alcohol and citral on staphylococcus aureus, jejunum bending bacteria, e. coli O157, single listeria and waxy bacillus activity also have inhibition effect. Ghasemzadeh et al. extracted tannin from the flowers of Etlingera elatior and found that it had inhibitory effects on Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Flavonoids from Bitter melon inhibited the growth of Escherichia coli, Pseudomonas aeruginosa, Shigella shigella, Salmonella, Staphylococcus aureus and Bacillus subtilis, and had the best inhibitory effect on Bacillus subtilis, with the minimum inhibitory concentration (MIC) values of the first three kinds of bacteria were 0.250 mg/mL, and the MIC values of the last three kinds of bacteria were 0.125 mg/mL. Forsythia extract can reduce the number of EScherichia coli in feces of piglets, and the diarrhea rate of piglets fed forsythia extract from 1 to 14 days was reduced by 61% compared with the control group.
With the increase of plant extract concentration, its bacteriostatic effect increased. LBP could inhibit the growth of enteric bacteria such as Escherichia coli, Salmonella and Staphylococcus aureus at appropriate concentration, and its inhibition to pathogenic bacteria became stronger with the increase of LBP concentration. Different volume fractions of aloe extracts can inhibit the growth of different bacteria, among which 5% aloe extracts can effectively inhibit the growth of Escherichia coli and Candida albicans, while when the volume fraction of aloe extracts is 20%, the growth of Staphylococcus aureus can be better inhibited.
The active ingredients in plant extracts can reduce the number of bacterial community and biogenic amine concentration in intestinal digesta, thus reducing the bacterial activity in ileum, jejunum and cecum, and promoting the stability of healthy microbial flora in intestinal tract of the body. Therefore, plant extracts have been gradually applied to promote intestinal health of animals. Adding the mixture of carvonol, cinnamaldehyde and capsaicin in the diet of piglets can reduce the number of EScherichia coli in jejunum, increase the number of lactobacillus and bifidobacteria, and reduce the diarrhea index of piglets, and the diarrhea rate decreased by 1.45% compared with the control group. 0.25% alfalfa saponin can significantly increase lactobacillus counts in duodenum, jejunum and caecum of piglets, 0.3% or 0.6% APS can also reduce the numbers of Escherichia coli and Salmonella, and increase the numbers of Lactobacillus and bifidobacteria in caecum of broilers, and the effect of 0.6% APS is more obvious.
As a new type of feed additive, plant extract has a wide range of antibacterial activities. It is worth mentioning that the bacteriostatic research on plant extracts at home and abroad is still in the stage of crude extract, and the research on its monomer components is less, which leads to the lack of clear standard for the addition amount of plant extracts. Therefore, it is particularly important to study the inhibitory effect of monomer components in plant extracts on bacteria and the appropriate addition amount in livestock and poultry diets
1.2 Promote intestinal health
Plant extracts can not only increase beneficial bacteria and inhibit harmful bacteria in the intestinal tract, but also improve the morphological structure of intestinal tissue, promote the expression of intestinal mucosal repair factor protein, reduce the level of intestinal inflammatory factors, promote the absorption and utilization of nutrients in the animal body, and ensure intestinal health. For example, adding 1 g/kg Acanthopanax senticosus micropowder and 1 g/kg acanthopanax senticosus micropowder into fresh milk can significantly increase the length and number of villi in duodenum, jejunum and ileum of lactating calves, and effectively reduce the occurrence of diarrhea and improve intestinal health of calves. Dietary supplemented with 0.2 g/kg phytosterol can significantly increase the villus height and crypt depth ratio of duodenum and jejunum, improve intestinal morphology, and decrease diarrhea rate of piglets. Baitulin can effectively increase the protein expression levels of intestinal mucosal repair factor EGFR and TGFβ1 in diarrhea mice, and significantly decrease the mRNA and protein expression levels of NF-κB P65 in diarrhea piglets. Yucca extract can increase the diversity of cecum microflora, maintain the structural integrity of intestinal tissue and regulate intestinal pH to maintain the levels of relevant immune proteins and promote intestinal health. Supplementation of 100 mg/kg grape seed anthocyanin in the basal diet of weaned piglets can significantly increase the villus height of duodenum and jejunum, significantly reduce the crypt depth of duodenum and ileum, improve the morphology of intestinal mucosa and promote the development of small intestine. By increasing the thickness of the mucus layer in the colon of mice, buticophenol can enhance the mucosal barrier and effectively prevent the invasion of pathogens and diseases.
As a new kind of functional feed additive, plant extract can promote intestinal health of animals. However, current studies on plant extracts in the intestinal health of livestock and poultry mainly focus on the intestinal environment, morphological structure and microflora, and there are few studies on the deep mechanism of improving intestinal barrier, mucosal immunity, especially tight junction protein, which can be explored in the future.
1.3 Enhance immunity
Plant extracts containing polysaccharides, saponins, alkaloids, essential oils and immune active ingredients such as organic acids, can promote the development of immune organs, increase the weight of immune organs, can also with the immune specific receptors on the cell membrane, adjusting T lymphocytes and B lymphocytes and macrophages secretion, enhance the immune power of the animal. 200 mg/kg bitter melon leaf extract can significantly increase serum IFN-γ and TNF-α levels in rats, stimulate cell-mediated immune response, thus enhancing immune properties, 50 mg/kg and 100 mg/kg bitter melon leaf extract can significantly increase serum TGF-β levels, enhance the anti-inflammatory ability of the body. Pulsatilla pulsatilla and pulsatilla pulsatilla saponins can increase the contents of TNF-α and IL-1β in serum, as well as the contents of IgG and IgM in serum of weaned piglets, and the effects of pulsatilla pulsatilla saponins and pulsatilla pulsatilla saponins were the best when the supplemental concentrations of pulsatilla pulsatilla saponins were 300 and 12.5 mg/kg, respectively. Phytochemicals containing cinnamon oil and citric acid can significantly reduce the number of fungi, aerobic bacteria and escherichia coli in small intestine, significantly increase the villus height and crypt depth of small intestine, and improve the immunity of broilers.
Natural plant extracts contain polysaccharides, saponins, alkaloids, essential oils and organic acids, which can effectively enhance the immunity of animals. However, the research on how plant extracts act on target organs and regulate various biological functions such as immunity is still in the preliminary stage, and needs to be further elucidated from the cellular and molecular levels.
