Supplementary of fibers in broiler diets can make beneficial effects on the growth performance, serological indexes and intestinal microbia, etc. For the growth performance, adding an appropriate amount of IDF in broiler diets can decrease the moisture content of the bedding (Kheravii et al., 2017), stimulate the development of chicken stomach (Donadelli et al., 2019), reduce fat deposition (Nassar et al., 2019), lower the pH of muscle stomach, improve nutrient digestibility (Jiménez-Moreno et al., 2019) and utilization rate (Nassar et al., 2019), so as to promote the growth of chicken (Donadelli et al., 2019). Adding 1% ~ 1.5% IDF-based cassava pulp modified fiber to broiler diets can reduce abdominal fat deposition, enhance muscle and stomach function and improve nutrient digestibility (Okrathok and Khempaka, 2020). Adding 3% ~ 6% insoluble fiber to wheat basal diet can improve the growth performance of broilers (Shirzadegan and Taheri, 2017). Similar results can be obtained by adding an appropriate level of structural IDF (Jiménez-Moreno et al., 2016). During the maturation and degeneration of lymphoid organs, adding IDF or mixture of IDF and SDF can promote the development of immune system of young birds and chickens (Hussein et al., 2017). However, the digestibility of organic matter and energy was decreased significantly when the level of fibers increased significantly (Röhe et al., 2020). Adding 3% ~ 6% insoluble fiber such as alfalfa meal, RB and sawdust in diet had no significant effect on slaughter performance of broilers (Shirzadegan and Taheri, 2017). In our study, adding 1% of MBP to broiler diet can improve the G: F and ADG, while it has no significant effect on ADFI, mortality, and most organ indexes. The results indicated that adding MBP to broiler diet was conductive to improving the growth performance of broilers, and the level of 1% was feasible. The dosage could be further tested and optimized from the aspects of organ development and slaughter performance.
In addition, the fiber from different sources also made different effects (Jiménez-Moreno et al., 2016). Jiménez-Moreno et al. (2019) showed that the addition of oat hulls was better than rice husks and sunflower hulls in improving muscle stomach weight, reducing muscle stomach pH and improving nutrient digestibility (Jiménez-Moreno et al., 2019). Our study indicated that the effects of adding MBP in broiler diet were better than that of RB, which may be related to the varied physical and chemical properties between the two fibers.
Dietary IDF can affect the serological parameters of broilers. MBP contains 0.94% ~13.4% of polysaccharide, 1.75%~16.89% of starch, 1.31%~2.03% of crude protein, and 62.54% ~ 89.79% of IDF (Felisberto et al., 2017). It was rich in bamboo leaf flavonoids and polysaccharides, which can regulate the immunity and anti-oxidant capacity of animals (Ge et al., 2020). Bamboo shoot shell fiber had strong cholesterol adsorption activity and prebiotic potential, which can be used as a prebiotic to promote the growth of lactic acid bacteria and increase the fermentability of substrates (Wu et al., 2020). For the mice with hyperlipidemia, it improved the disorder of fat metabolism, reduced the contents of serum cholesterol, triglyceride, low-density lipoprotein cholesterol, and increased the content of high-density lipoprotein cholesterol (Luo et al., 2017). Our study indicated that the addition of MBP regulated the serum biochemical indexes. Compared with RB, the MDA and serum glucose were significantly decreased in broilers fed with MBP. Further, the serum urea nitrogen also tended to be decreased. Chicken can be applied as biological model of growth and development (Vainio and Imhof, 1995; Hillier LaDeana, 2004). The addition of 1.0% IDF-based cassava modified fiber in broiler diet can lower serum cholesterol (Okrathok and Khempaka, 2020). It is consisted with the results obtained in our study. The addition of fibers from different source can significantly reduce the serum glucose, triglyceride, and total cholesterol in broilers, while significantly increasing the serum glutathione peroxidase activity. The fibers of RB and MBP are mainly made of IDF, indicating that IDF-based fiber material is helpful to improve serum glucose and lipid metabolism of broilers.
The intestinal microbial community has been very important to the host (Ji et al., 2019), which may affect the intestinal function through its metabolites of SCFAs (Clausen and Mortensen, 1995), thus making effects on the nutrition, immunity and physiological states of the host (Ussar et al., 2016; Imhann et al., 2018; Rubio, 2019). As we all know, cecum can digest some carbohydrates which cannot be digested by small intestine, including cellulose, starch and polysaccharide (Clench and Mathias, 1995). Cecal SCFAs were produced by intestinal microorganisms through the fermentation of undigested carbohydrates (Den Besten et al., 2013; Li, 2018). Awad et al.(2016) found that the variations of fermentation products may be related to the density of microflora (Awad et al., 2016). The highest diversity and abundance of microbial flora has been observed in cecum (Gong et al., 2007; Choi et al., 2014; Liao et al., 2020). After exploring different parts of intestines, it was also found that SCFAs were the most abundant in the cecum (Liao et al., 2020). The difference of SCFAs between small intestine and cecum may be related to the intestinal transportation, intestinal pH and microbial composition (Macfarlane and Macfarlane, 2012). Therefore, our study has also focused on SCFAs in the cecum of broilers.
Previous studies have revealed that the SCFAs can significantly affect the intestinal health, which is closely related the microbials in the intestine. Acetic acid inhibited gastric cell apoptosis and promoted mucin production (Liu et al., 2017), while butyric acid provided energy, maintained the integrity of intestinal epithelial cells and stimulated the growth of intestinal tract (Sun and O'Riordan, 2013). It was found that cecal infusion of butyrate stimulated the proliferation of jejunum and ileum cells in piglets (Kien et al., 2007). Butyrate in cecum may be sent back to the small intestine through reverse peristalsis, thus promoting the development of the small intestine. Lactic acid bacteria was positively correlated to acetate in ileum (Liao et al., 2020), which can improve intestinal health by producing some certain SCFAs (He et al., 2019; Zhai et al., 2019). Salmonella was negatively correlated with SCFAs including acetic acid, butyric acid and isovaleric acid (Liao et al., 2020), indicating that cecal SCFAs may inhibit the growth and invasion of salmonella (Lawhon et al., 2002).
SCFAs can be changed with the diet. Furthermore, when the level of cellulose was increased, SCFAs decreased significantly (Röhe et al., 2020). In addition, it was found that adding a small amount of fiber in diet of weaned piglets tended to increase the VFA in feces. The amount of lactic acid bacteria and total VFA in feces would be increased significantly under poor sanitary conditions (Mu et al., 2017). In our study, adding 1% MBP had no significant effect on the composition of SCFAs in cecal chyme of broilers (including acetic acid, butyric acid, propionic acid, isobutyric acid, isovaleric acid, valeric acid, etc.), while the levels were increased. It may also be related to the supplementary dosage and culture environment. Further study should be performed to explore whether MBP can promote intestinal health and growth by regulating fermentation and producing SCAFs.
Dietary composition is an important factor affecting intestinal bacteria (Liao et al., 2020). The microbial abundance and diversity in feces could be improved by increasing the levels of dietary fibers, which were indicated by Chao and Shannon indexes (Jiang et al., 2019). Mu et al. (2017) found that alfalfa diet can increase the diversity of intestinal flora in piglets (Mu et al., 2017). The cecal microbial diversity was rich in birds (Liao et al., 2020). Our study revealed that the addition of MBP significantly reduced the evolution diversity index Faith_pd of cecal chyme microorganism, and tended to reduce the richness index Chao1. The decrease of diversity index is conductive to reducing the nutrient consumption of microbial flora, thus improving the growth performance.
The composition of microflora was complex in gastrointestinal tract of chicken (about 107-1011 CFU/g), among which Firmicutes were the most abundant, followed by Proteobacteria and Bacteroidetes (Apajalahti et al., 2004; Sergeant et al., 2014; Xiao et al., 2017). During the growth stage of broilers, the dominant flora in cecum were thick-walled bacteria such as Faecalibacterium, Ruminococcus and Lachnospiraceae, while the dominant flora in cecum were Bacteroidetes in the later growth stage. Studies have found that Ruminococcus was the main microflora that produced SCFAs in the intestine (Li et al., 2018), which was positively correlated with the production of butyric acid (Liao et al., 2020). Trichinella can promote intestinal development and health by degrading plant fiber and producing SCFAs (Biddle et al., 2013). Bacteroidetes can degrade complex carbohydrates by fermenting glucose to synthesize butyric acid as energy of epithelial cells (Macy and Probst, 1979), and the abundance of Bacteroidetes in cecum was positively correlated with butyric acid concentration (Liao et al., 2020).
The source and structure of dietary fibers can affect the regulation of intestinal flora in broilers. Adding inulin (contained mainly SDF) to broiler diet made greater effects on microflora, however, its effects on weight gain was less than that of inulin and bran combination group (Li et al., 2018). Adding 2% lignocellulose can reduce Clostridium, without affecting the amount of Bifidobacterium, Bacteroides, Bacillus and Lactobacillus (Kheravii et al., 2017). It has been found that amorphous cellulose with IDF as the main component can change the composition of microflora at the level of Bacteroidea in the chyme, especially Alistipes (De Maesschalck et al., 2019). However, when the level of cellulose increased significantly, Shigella chymotryi decreased significantly (Röhe et al., 2020). In this study, the addition of MBP tended to increase the richness ratio of Firmicutes and Flavonifractor in cecal chyme of broilers, while the addition of RB decreased the ratio of Firmicutes and increase the ratio of Bacteroides, the abundance ratio of Festuca and Bacteroides was also increased. Further results indicated that the addition of MBP made great effects on cecal chyme flora of broilers, in which the abundance of Muribaculum and Veillonellaceae were significantly reduced, and the abundance of Collinsella was significantly increased. It indicated that MBP can not only regulate the richness and diversity of microflora, but also affecting their composition.
Similar results can be obtained by typical chromatogram analysis and metabolic component cluster analysis on the cecal chyme of broilers. The addition of MBP and RB can both affect the total ionic strength and component clustering of cecal chyme metabolites in broilers. It indicated that the addition of IDF can change the specie and concentration of metabolites, thus affecting the cecal chyme metabolism. It was also confirmed by the further analysis of metabolic pathways. Compared with the control, the differential metabolic pathways after the addition of MBP were mainly fatty acid metabolism, amino acid metabolism and intestinal immune IgA production. In addition, the effects of adding different IDF on metabolic pathways also varied. The differences between adding MBP and RB were mainly pathways responsible for amino acid metabolism and fatty acid metabolism.
Fibers play the role of prebiotics in cecal digestion of animals, promoting the selection of healthy intestinal microflora (Kheravii et al., 2017; Donadelli et al., 2019). It is still necessary to further explore the mechanism on the effects of adding MBP in broiler diet. The analysis of differential metabolic pathway confirmed the effects of MBP. Further study can be focused on the fatty acid metabolism, amino acid metabolism and intestinal immune IgA production.