Effects of Fermented Feed on Growth Performance and Intestinal Microorganisms of Hebei Meat Geese

Herein, to explore the effect of fermented goose feed on meat geese, the growth


INTRODUCTION
F eeds play a significant role in breeding; however, the macromolecular substances cannot be decomposed entirely and absorbed, which may easily elevate the intestinal tract burden and cause animal diseases (Feng et al., 2006;Pourabedin and Zhao, 2015). Of note, intestinal microflora plays a vital role in host metabolism regulation. In case the intestinal function or the dynamic balance of intestinal microflora is impaired, the digestion, metabolism, and utilization of nutrients is severely affected, resulting in reduced feed utilization rate and an increase in livestock and poultry mortali (Dibner and Richards, 2005).
As a new type of biological feed, fermented feed improves the structure of nutrients through probiotic fermentation (Song et al., 2010). Nutrients that can hardly be utilized by animals are decomposed into small molecular active peptides and monosaccharides readily absorbed.
Similarly, various digestive enzymes, amino acids, and vitamins produced during the growth and metabolism of the bacterial strain, which enhances nutrient absorption in the animal body (Shi et al., 2015), improve the nutritional level of feed (Yeh et al., 2018), and improve the average daily gain and daily feed intake (Koo et al., 2018). At present, studies have revealed the effectiveness of fermented feed in improving nutrition levels. For instance, feeding on fermented feed was found to significantly increase the daily gain and daily feed intake of growing and finishing pigs, whereas the conversion efficiency of feed was improved considerably (Shi et al., 2015). Also, the apparent digestibility of crude protein and neutral detergent fiber was higher than that of the control group.
Fermented feeds have a stable microbial system, which potentially promotes the colonization of intestinal probiotics and improves the dynamic balance of animal intestinal microflora (Kim et al., 2011). Intestinal microflora mediates physiological functions such as digestion and absorption of nutrients (Ubeda et al., 2017); this not only can provide nutrition for animals directly but also activate essential enzymes (acid protease, amylase, lipase, and cellulose), thereby improving the efficiency of protein and energy utilization (Sears, 2005;Begg et al., 2014). By adjusting intestinal peristalsis, regulating the dynamic level of immunity, microorganisms can O n l i n e

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effectively resist the infection of exogenous pathogenic bacteria, inhibit the colonization of pathogenic bacteria in the intestinal tract (Munns and Tester, 2008), improve the body immunity (Pourabedin and Zhao, 2015), reduce the incidence of animal diseases (El et al., 2014), and maintain the intestinal health of the host. Several microorganisms have been widely used in feed fermentation, and many scholars have confirmed the driving effect of some of these microorganisms on fermentation (Wang et al., 2014;McAllister et al., 2018). Currently, yeast and Bacillus are the commonly used strains in feed fermentation (Cheng et al., 2020). As a probiotic, yeast has been used in livestock and poultry feed for a long time and plays a significant role in maintaining intestinal health and enhancing immunity (Murray et al., 2016;Nelson et al., 2018). Yeast produces a variety of metabolites during growth, which improve the growth performance of livestock and poultry and adjust the dynamic balance of intestinal microflora (Shurson, 2018). In this study, Bacillus subtilis, as a safe feed addition strain, was applied to ferment compound feed; it sporulates in extreme conditions and can resist high temperature, oxidation, and salt concentrations. Moreover, B. subtilis remain active in feed processing, is highly stable (Nicholson et al., 2000), and can secrete several enzymes, including amylase, protease, lipase, cellulase, etc., which efficiently degrade xylan, cellulose, and other macromolecular substances, and eliminate anti-nutritional factors in the feed. Thus, both feed quality and nutrition level are improved (Priest, 1977). At the same time, B. subtilis can release various ester peptide antibiotics to help animals resist pathogenic infection and maintain intestinal integrity; this has inestimable potential in biological control (Zhang et al., 2017). Hence, this study purposed to evaluate the effect of fermented feed on growth performance and intestinal flora of geese through a feeding experiment. Further, it validates the application of fermented feed of B. subtilis N-10 in poultry breeding, and provides new germplasm resources for fermented feed.

MATERIALS AND METHODS
The experiment was conducted at the JIWEI Biological technology Co., Ltd. of Baoding City, Hebei Province, China, from June to September 2019, in accordance with the ethical guidelines for the protection and use of experimental animals formulated by Hebei Agricultural University and the Regulations on the Administration of Experimental Animals in China.
A total of 300 Hebei geese from 1 to 7 days old were housed on the floor. At 7 days, 270 healthy birds of similar body weight were selected and randomly assigned to 3 treatments. Each treatment had 3 replicates. Every replicate contained 30 geese. Birds in each treatment were fed on a basal diet supplemented with 0.0 (et 1), 5.0% (et 2), or 7.5% (et 3) fermented feed. The diets were offered to animals ad libitum, and we availed water throughout the trial. The experiment lasted 70 days. There were no significant differences in initial body weight (BW) among the treatments. The diet components and nutritional levels are highlighted in Table I.
The fermented feed was obtained from Hebei Forage Microbiology Research Center (Hebei, China). Before fermentation, B. subtils N-10 with 1×10 12 CFU/g was inoculated in the basic geese feed (Provided by LINGYUN Feed Manufacturing Co., Ltd.). After thoroughly mixing in a blender, the feed was put into a fermentation bag with a one-way breathable valve and fermented for not less than 7 days at room temperature. Determining growth performance During the 70 days feeding period, the total feed intake was recorded for each bird. On day 70, birds (with empty stomachs) were weighed in the morning to O n l i n e

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determine the average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR). The FCR was calculated as: The gram of feed consumed per gram of body weight gained (Sun et al., 2020).

Determining nutrient utilization efficiency
On day 70 of the trial, one bird in each replicate of each treatment was selected; after we stopped feeding them for 1 day, provided free drinking water for 3 days, and fed on a 120 g diet every day. The feces were collected using the total fecal collection method for 3 consecutive days. Fecal samples were collected, dried, and crushed at 75°C. The content of crude protein (CP) was determined by an automatic Kjeldahl nitrogen meter, whereas the contents of crude fiber (CF), neutral detergent fiber (NDF), and acid detergent fiber (ADF) were determined using an automatic fiber analyzer.

Determining slaughtering performance
On day 70 of the trial, all the birds were sacrificed through bleeding from the jugular vein. Then, the chest muscle rate, leg muscle rate, dressing percentage, eviscerated rate, and semi-eviscerated rate were calculated.

Determining biochemical and immune indexes
On day 70 of the trial, one bird in each replicate of each treatment was selected. 10 mL of blood was collected from the vein and centrifuged for 10 min at 5000 r/min. Serum was collected in a 1.5 mL tube and stored at -20°C serum biochemical index and immune index analyses. The activities of alkaline phosphatase (AKP), acid phosphatase (ACP), glutamic pyruvic transaminase (ALT), glutamic oxaloacetic transaminase (AST), immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM), interleukin-1 (IL-1), interleukin-2 (IL-2), interleukin-6 (IL-6) and tumor necrosis factor-α (TNFα) were measured. All serum biochemical and immune indexes were detected using kits. All kits are purchased from Wuhan Moshak Biotechnology Co., Ltd., and the detection methods were carried out in strict accordance with the procedures recommended by manufacturers.

Determining intestinal microorganisms
At the end of the experiment, one bird from each replicate of every treatment was selected, killed by venous bloodletting. Subsequently, the cecum contents were transferred into a sterile EP tube and quickly placed in liquid nitrogen, then stored in a refrigerator at-80°C. According to the manufacturer's instructions, the microbial community genomic DNA was extracted using the E.Z.N.A.® soil DNA Kit (Omega Bio-tek, Norcross, GA, U.S.). DNA extract was checked on 1% agarose gel, and DNA concentration and purity were determined with NanoDrop 2000 UV-vis spectrophotometer (Thermo Scientific, Wilmington, USA). The hypervariable region V3-V4 of the bacterial 16S rRNA gene were amplified with primer pairs 338F (5'-ACTCCTACGGGAGGCAGCAG-3') and 806R (5'-GGACTACHVGGGTWTCTAAT-3') by an ABI GeneAmp® 9700 PCR thermocycler (ABI, CA, USA). PCR amplification of the 16S rRNA gene was performed as follows: Initial denaturation at 95°C for 3 min, followed by 27 cycles of denaturation at 95°C for 30 s, annealing at 55°C for 30 s, extension at 72°C for 45 s, and single extension at 72°C for 10 min, and kept at 4°C. The PCR mixtures contained: 5 × TransStart FastPfu buffer 4 μL, 2.5 mM dNTPs 2 μL, forward primer (5 μM) 0.8 μL, reverse primer (5 μM) 0.8 μL, TransStart FastPfu DNA Polymerase 0.4 μL, template DNA 10 ng, and volume made up to 20 μL with ddH 2 O. PCR reactions were performed in triplicate. The PCR product which was located at 468 bp band was extracted from 2% agarose gel and purified using the AxyPrep DNA Gel Extraction Kit (Axygen Biosciences, Union City, CA, USA) according to the manufacturer's instructions and quantified using Quantus™ Fluorometer (Promega, USA). Purified amplicons were pooled in equimolar and pairedend sequenced on an Illumina MiSeq PE300 platform/ NovaSeq PE250 platform (Illumina, San Diego, USA) according to the standard protocols by Majorbio Bio-Pharm Technology Co., Ltd. (Shanghai, China).

Statistical analysis
The test data were analyzed using the ANOVA program of SPSS19.0 statistical software. Data with significant differences were compared via Duncan's method. P < 0.05 signified significant differences. Data generated from the Illumina platform were used for bioinformatics analysis. All analyses were performed using the I-Sanger Cloud Platform (www.i-sanger.com) from Shanghai Majorbio.

Growth performance
At 70 days old, the average weight of et1, et2, and et3 was 3.59 kg, 3.67 kg, and 3.79 kg, respectively. Compared to et1, both et2 and et3 significantly increased their body weight by 2.22% and 5.57% (P < 0.05, Table II). The ADG increased significantly by 2.03% and 5.52% (P < 0.05), and the ADFI increased by 2.25% and 3.06%, respectively, with no significant difference (P > 0.05, Table II). However, no significant difference was reported in FCR among the three experimental groups.

Nutrient utilization efficiency
At the end of the experiment, the nutrient utilization

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efficiency of the two experimental groups was significantly improved. Among them, the utilization rate of CP, CF, NDF, ADF by et2 increased by 1.84%, 1.98%, 1.98%, and 1.22% (P < 0.05, Table III), whereas the utilization rate of CP, CF, NDF, ADF by et3 increased by 3.64%, 3.45%, 5.14% and 2.36% (P < 0.05, Fig. 1A). Results showed that the addition of fermented feed could improve the growth performance of the body and improve the nutrient utilization rate. The effect was best at 7.5% proportion of the fermented feed.

Slaughtering performance
Post-slaughtering data analysis revealed no significant differences in semi-eviscerated rate, eviscerated rate, chest muscle rate, and leg muscle rate among the three groups (P > 0.05, Fig. 1B). Compared to et1, the slaughtering rate of et2 and et3 was higher. Notably, the slaughtering rate of et3 was significantly increased by 4.25% (P < 0.05, Fig. 1B).

Blood test results
Compared to et1, AKP and ACP in et 2 and et 3 were lowered significantly (P < 0.05, Fig. 2A), whereby AKP decreased by 17.65% and 47.06%, respectively, and ACP by 10.52% and 31.57%, respectively. No significant change was reported in other blood biochemical and immune indexes (P > 0.05, Fig. 2B, C). , values with superscripts of different letters in the same row were significantly different (P <0.05),whereas values with the same or no superscripts showed no differences (P ≥ 0.05). , values with superscripts of different letters in the same row were significantly different (P<0.05),whereas values with the same or no superscripts showed no differences (P ≥ 0.05).

Bacterial community compositions
After the raw sequences obtained from lllumina MiSeq were assembled and screened, a total of 547,210 high-quality, effective sequences were obtained, with the effective base number of 228, 721, 1085 bp, and the average sequence length of 418 bp (Table III). All samples attained the same sequencing depth, from which we generated sample diversity. To identify the differences in microbial species among samples, we determined the β diversity of samples using principal component analysis (PCA). The three experimental groups were well separated, and the principal components PC1 and PC2 explained the variation of 20.0% and 16.37%, respectively (Fig. 3). However, et3 and et1 were in a discrete state, indicating that the change in intestinal flora was related to the addition of 7.5% fermented feed. Similarly, the Shannon index of et3 decreased from 1.7932 to 1.6051 (P < 0.05, Table III), whereas the Simpson index of et3 increased from 0.1939 to 0.2640 (P < 0.05, Table III). By analyzing the structure of meat geese, we found that the intestinal flora was dominated by bacteria. At the phylum level, Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were found to exhibit precise classification. The effects of different treatments on the abundance of Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were not significant (P > 0.05, Fig. 4A  As depicted in Figure 4B, Prevotella and Bacteroides were the most dominant bacteria in the three treatment groups; notably, Prevotella was one of the most dominant bacteria. The abundance of Prevutella, Bacteroides, and Stenotrophomonas increased, whereas the abundance of Escherichia-shigella and Turicibacter decreased in the two experimental groups. We standardized the OTU abundance table by PICRUSt. Here, COG and KEGG functions of OTU were annotated, and the annotation information of OTU at each function level of COG and KEGG and the abundance information of each function in different samples were obtained. In the experimental group, the functional levels of Carbohydrate Metabolism and Amino Acid Metabolismwere the highest. Besides, the two experimental groups showed improved functional levels of the Histidinekinase (COG0642), Glycosyltransferase (COG0438), Acetyltransferase (COG0456), Alpha Beta Hydrolase (COG0596), Methyltransferase (COG2226), Oxidoreductase (COG0673), Guanylate cyclase (COG2199), Alpha Amylase (COG0366), and other functions (Fig. 5).

DISCUSSION
Feeds are essential components in livestock and poultry breeding. The standard formula feed contains numerous macromolecular nutrients, yet livestock and poultry do not possess enough endogenous enzymes to digest and utilize these nutrients. This reduces feed conversion efficiency, leading to an increase in the intestinal burden. Consequently, livestock and poultry are more likely to develop diseases and are characterized by a reduced growth rate. Further, the anti-nutritional factors in feed hinder the absorption and utilization of nutrients (Song et al., 2010). Fermentation is an effective strategy to convert the flavor and nutritional value of feed, which can significantly improve the nutritional level of feed and promote the absorption and utilization of nutrients by livestock and poultry (Peralta et al., 2008). After the feed is fermented, the macromolecular substances which cannot be absorbed and utilized by animals are degraded by microorganisms into small molecular substances into easily digestible and utilizable forms. The elimination of anti-nutritional factors in feed is also beneficial to animals (Wang et al., 2019).
In this study, by adding a different proportion of fermented feed to the diet, we reported improved ADG and ADFI levels of geese at different degrees. With an additional 7.5%, the ADG was significantly improved (5.52% P < 0.05, Table II). Although ADFI was improved, the difference was not significant (3.06% P > 0.05, Table II). This demonstrates that the improvement of the growth performance of meat geese cannot be achieved by increasing feed intake . The improved growth performance of livestock and poultry is attributed to improved digestive capacity. In contrast, the fundamental mechanism for improving digestive capacity is to increase the activity of digestive enzymes in the intestine and accelerate the decomposition of nutrients in the feed (Youssef et al., 2020). Moreover, to improve the growth performance of geese, we used B. subtilis fermented feed instead of a 7.5% common formula feed. Notably, protease, amylase, cellulase, and other digestive enzyme-producing bacteria could be used in feed pretreatment to decompose macromolecular nutrients into small molecular nutrients for livestock and poultry, which was similar to the results of previous studies (Supriyati et al., 2015;Ye et al., 2017). It is worth noting that when the fermented feed was used instead of different proportions of formula feed, the content O n l i n e

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Y. Sun et al. of CP, CF, NDF, ADF in feces decreased significantly. However, with an increase in the proportion of fermented feed, the content of CP, CF, NDF, ADF in feces decreased. Besides, we found a positive correlation between growth performance and nutrient digestibility (Park et al., 2020). This demonstrates that after consuming fermented feed, the utilization rate of protein and crude fiber is higher in geese and the lignin, cellulose, and hemicellulose which can hardly be decomposed into small molecular carbohydrates, ready for absorption and utilization by livestock and poultry under the action of microorganisms (Mukherjee et al., 2016). At the same time, these carbohydrates produce volatile organic compounds such as lactic acid and acetic acid in the metabolic process of probiotics, which improve the palatability of livestock and poultry and are conducive to feed preservation. So far, numerous studies have proved the effectiveness of fermented feed in improving the growth performance of livestock and poultry. By feeding broilers with feed fermented by B. subtilis, the daily gain of broilers significantly increased at the end of the experiment (Yeh et al., 2018). Other scholars have also reported that fermented feed can increase the content of CP in feed, reduce the content of CF, thereby improving the nutritional utilization rate of broilers (Xu et al., 2012;Khempaka et al., 2014;Olukomaiya et al., 2019). Of note, the improved absorption and utilization of nutrients by livestock and poultry results in a better slaughtering performance of geese. Slaughtering percentage is an important basis to measure animal slaughtering performance (Li et al., 2018). Herein, we found that with 7.5% fermented feed, instead of diet, the slaughtering rate was significantly increased. Besides, when 5% of fermented feed was used instead of diet, the slaughtering rate was raised, but the difference was not significant. Based on previous reports, the increased slaughtering rate showed that the animal body could effectively utilize nutrients in feed. In contrast, the addition of fermented feed promoted the digestion and absorption of nutrients such as crude protein and crude fiber in the goose intestine. These findings are consistent with our present results, whereby the addition of different proportions of fermented feed significantly improved the growth performance of geese. However, whether the addition of fermented feed or probiotics would have adverse effects on animals remains elusive. Therefore, further studies are warranted to determine the physiological and biochemical indexes and immune indexes of geese. Moreover, serum immune indicators reflect the physiological and immune status of livestock and poultry, the metabolism of nutrients, the dynamic balance of the internal environment, and the health status of animals . Pathological changes induce the animal body to secrete many immune factors that mediate immune response and resistance to epidemic diseases. At the same time, due to a poor diet in daily life, animals liver function under long-term load, which is easy to produce cell rupture, bleeding lesions, and so on. Consequently, glutamic pyruvic transaminase activity in serum is significantly increased (Sudre et al., 2005).
In this experiment, blood analysis revealed that compared to non-fermented feed, the addition of different proportions of fermented feed to the diet increased the AKP significantly. Meanwhile, the difference between ACP, AST, ALT, IgA, IgG, IgM, IL-1, IL-2, IL-6, and TNF-α was not significant but showed a general downward trend. When the animal is in good health, AKP binds closely to the cell membrane, and the content of AKP in serum is less. Once pathological changes occur in the liver system, the diseased cells and tissues excessively release AKP into the serum, increasing the activity of AKP in the serum (Poupon, 2015). Compared to the group without fermented feed, the activity of AKP in the experimental group decreased, indicating that the addition of different proportions of fermented feed could promote liver tissue, and reduce the risk of bile duct obstruction, liver cell damage, bile duct epithelial regeneration and carcinogenesis; however, 7.5% fermented feed showed a better effect. From these observations, it is evident that fermented feed can promote the metabolism and physiological state of the animal body. Besides, the addition of different fermented feed proportions has no adverse effect on the animal body (Shi et al., 2015). This may be explained by the phenomenon that B. subtilis N-10 can produce various ester peptide antibiotics, which have inhibitory activity against various intestinal pathogens, thus reducing the occurrence of inflammation.
To further reveal the relationship between fermented feed and improved growth performance of geese, we explored the intestinal microbial diversity of different experimental groups. Numerous studies have found a close relationship between fermented feed and intestinal microorganisms (Wu et al., 2011). Compared to the group without fermented feed, the Shannon of the 7.5% fermented feed group was significantly lower, whereas the Simpson was substantially higher. Furthermore, the Shannon and Simpson of the 5% fermented feed group was not significant. Of note, Shannon and Simpson reflect the diversity of microorganisms, where the larger the Shannon and Simpson are, indicating that the microbial diversity is higher (Wang et al., 2012). The addition of exogenous bacteria caused a temporary decrease in intestinal microbial diversity, which reasonably explained the decrease of shannon in the experimental group. However, the addition of exogenous bacteria may become the dominant bacteria in the intestinal flora, which O n l i n e

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Effects of Fermented Feed on Hebei Meat Geese 9 reasonably explains the increase of Simpson (McAllister et al, 2018). Based on PCA analysis, the three groups had a good degree of separation, with each sample exhibiting a good repetition. Among them, 7.5% of the fermented feed group was in a discrete state, and the 5% fermented feed group did not overlap with the group without fermented feed. However, it was close to the group without adding the fermented feed. We also found that the intestinal microorganisms of geese changed after adding different proportions of fermented feed, which may be related to the introduction of new microflora. For this reason, we analyzed the composition of intestinal microorganisms in geese at the gate level and genus level, respectively. At the phylum level, Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria exhibited a precise classification (Yan et al., 2019). The abundance of Firmicutes and Bacteroidetes was the highest among the three experimental groups (Singh et al., 2013). As the most dominant flora, the abundance of Firmicutes was the highest, followed by Bacteroidetes. When we added different proportions of fermented feed to the geese diet, the abundance of Firmicutes and Bacteroidetes in the two experimental groups increased, whereas the 7.5 fermented feed group increased even more. Studies have shown that the absorption of nutrients in the intestinal tract of animals is influenced by intestinal flora (Kogut, 2019). Firmicutes and Bacteroidetes are closely related to the absorption and utilization of energy, potentially converting complex carbohydrates into short-chain fatty acids and regulating the metabolism of nutrients in animals (Benítez-Páez et al., 2016;Park et al., 2017). Firmicutes can effectively degrade high molecular compounds such as carbohydrates and proteins in the intestines, helping the animal bodies obtain nutrients from feed (Tremaroli and Bäckhed, 2012). We believe that the increased abundance of Firmicutes is related to the addition of B. subtilis to ferment feed. Bacteroidetes utilize complex polysaccharides in the intestinal tract as sources of carbon and energy, releasing the final fermentation products, which provide nutrients to the animal body and confer other beneficial properties to the host (Comstock, 2009). In the present study, after adding different proportions of fermented feed, the ADG of geese increased, indicating that the abundance of Firmicutes and Bacteroidetes are positively correlated with the growth performance (Yan et al., 2019).
At the genus level, the abundance of Prevotella and Bacteroides in the intestinal tract of geese increased after adding different proportions of fermented feed. Notably, Prevotella can degrade and utilize starch and plant cell wall polysaccharides, such as xylan, pectin, and others, to exert critical function in protein degradation, peptide absorption, and fermentation (Bekele et al., 2011). Some Prevotella also produce carboxymethyl cellulase. After fermentation, high molecular substances such as cellulose are degraded into hemicellulose and oligosaccharides, which enhance the absorption of nutrients in the intestinal tract of geese under the action of microorganisms. Bacteroides harbor a large number of genes for polysaccharide catabolism (Magnúsdóttir et al., 2017). Genes expressing carbohydrate-degrading enzymes (not found in animals) can degrade indigestible macromolecular carbohydrates in food to glucose and other digestible small molecular sugars that can be absorbed directly (Sonnenburg et al., 2005). Bacteroides can also produce propionate (Corrigan et al., 2015), reducing colitis incidence (Tong et al., 2016). Unexpectedly, in our work, at the genus level, Bacillus did not rank in the top 10 with the highest abundance. Thus, we speculated that although the addition of B. subtilis N-10 increased the abundance of the phylum, it may be because the strain was not adequately colonized in the goose intestine. This finding should further be explored.
The functional prediction of the geese intestinal microflora, our results demonstrated that feeding on different proportions of fermented feed improves the levels of carbohydrate metabolism and amino acid metabolism. Studies have reported that more than 35% of the enzymes needed for digestion and metabolism in animals are secreted by intestinal microorganisms, of which 25% are related to carbohydrate metabolism (Gill et al., 2006). Protein, the most critical nitrogen source in the animal diet, is decomposed by microbial hydrolases to produce peptides and amino acids (Varisi et al., 2008). Amino acids are derived from pyruvate under the action of combined deaminases and dehydrogenases. Pyruvate is a weakly acidic organic acid, which plays a vital role in the metabolism of three major nutrients (sugars, fats, amino acids). It is the final product of glycolysis, which is oxidized to acetyl-CoA within the mitochondria, enters the tricarboxylic acid cycle, and completes the aerobic oxidation glucose. The conversion of sugars, fats, and amino acids can also be completed via the tricarboxylic acid cycle (Brüggemann and Gottschalk, 2004). The improved carbohydrate transport and metabolism and amino acid transport and metabolism can enhance nutrient absorption and promote the metabolism of proteins, carbohydrates, inorganic ions, and nucleic acid in geese. The present study reported a significantly improved utilization of nutrients in the intestinal tract of geese, which promoted the growth of geese.

CONCLUSION
The present study demonstrates that the addition of different proportions of fermented feed positively impacts O n l i n e

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Y. Sun et al. the growth performance and intestinal flora composition of geese, which may improve the nutritional status and intestinal health of the host. Additionally, feeding different proportions of fermented feed could enhance the growth performance of geese by improving the dynamic balance of cecal microflora. According to these changes, we can conclude that adding different proportions of fermented feed to the goose diet can change the composition of goose intestinal microflora, which is beneficial to the healthy development and growth performance of the goose intestine. We demonstrated that these effects are best achieved when the proportion of fermented feed is 7.5%.