Acta Veterinaria et Zootechnica Sinica ›› 2023, Vol. 54 ›› Issue (10): 4260-4277.doi: 10.11843/j.issn.0366-6964.2023.10.023

• ANIMAL NUTRITION AND FEEDS • Previous Articles     Next Articles

Effect of Dietary Fiber Level on Blood and Intestinal Immune Indexes of Meishan Pigs and Preliminary Analysis of Its Mechanism

LI Pinghui1,2, PU Guang1,2, WANG Zhongyu1,2, ZHOU Wuduo1,2,3, NIU Peipei2, WU Chengwu2, HOU Liming1,2,3, HUANG Ruihua1,2,3*, LI Pinghua1,2,3*   

  1. 1. Institute of Swine Science, Nanjing Agricultural University (Key Laboratory of Evaluation and Utilization of Livestock and Poultry (PIG) Resources, Ministry of Agriculture and Rural Affairs (Nanjing)), Nanjing 210095, China;
    2. Huaian Academy, Nanjing Agricultural University, Huai'an 223001, China;
    3. Industrial Technology System Integration Innovation Center of Jiangsu Modern Agriculture (PIG), Nanjing 210095, China
  • Received:2023-02-21 Online:2023-10-23 Published:2023-10-26

Abstract: This study aimed to analyze the effects of different levels of wheat bran replacing basal diet on blood routine, blood biochemistry, serum immunoglobulin, and large intestinal mucosal secretory immunoglobulin A (SIgA) of Meishan pigs, using Large White pigs as the control. Then further studied the mechanism of dietary fiber affecting the immune indicators of Meishan pigs from the perspective of host intestinal genes and microorganisms. In this study, 28 Meishan pigs (initial body weight was (67.08±1.53) kg) and 28 Large White pigs (initial body weight was (81.04±1.64) kg, at the same physiological stage as Meishan pigs) were randomly and respectively divided into 4 treatment groups with 7 replications in each group for 1 per duplicate. During the pre-feeding period of 7 days, all pigs were fed the basal diet, and during the main trial period of 28 days, they were fed with the basal diet (Basal), 7%, 10.5%, and 14% wheat bran substituted in the basal diet (7% WBR, 10.5%WBR and 14% WBR), respectively. During the trial period, all pigs had free access to food and water. At the end of the experiment, all pigs were slaughtered, and blood samples were collected for the determination of blood routine, blood biochemical and serum immunoglobulin indicators. Cecal and colonic mucosal samples were collected for SIgA determination, and colonic mucosal were collected to perform RNA-seq. Colonic contents were collected for metagenomic sequencing. The results showed that:1) With the increasing of wheat bran replacing basal diet level, the number of eosinophils and basophils, and percentage of eosinophils decreased in Meishan pigs linearly, (P<0.05), and the serum globulin level of Meishan pigs in the 14% WBR group were significantly higher than that of Large White pigs (P<0.05). 2) With the increasing of wheat bran replacing basal diet level, the serum immunoglobulin M (IgM) and immunoglobulin G (IgG) of Meishan pigs increased linearly, (P<0.01), and the serum IgM of Large White pigs increased (linear, P<0.01). The serum IgG concentration of Meishan pigs in the 14% WBR group was significantly higher than that of Large White pigs (P<0.01). In addition, compared with the Basal group, the concentration of colonic mucosal SIgA of Meishan pigs in the 14% WBR group was significantly increased (P<0.01), but there was no significant change between the 14% WBR group and the Basal group in Large White pigs. 3). To elucidate the mechanism of increased colonic mucosal SIgA concentration of Meishan pigs in the 14% WBR group, on the one hand, the colonic mucosa of Meishan pigs in the Basal group and the 14% WBR group were selected to perform RNA-seq. A total of 38 differentially expressed genes were identified, and the functional items enriched by GO and the signaling pathways enriched by KEGG were mainly related to the immune system. The expression of CD4 molecule (CD4) and C-C chemokine receptor 9 (CCR9) regulating intestinal SIgA production was significantly increased in the 14% WBR group (P<0.05). On the other hand, the colonic contents of Meishan pigs in the Basal group and the 14% WBR group were selected to perform metagenomic sequencing. The results of LEFSe analysis showed that 14% WBR group was significantly enriched to 2 family-level microorganisms, 1 genus-level microorganism, and 5 species-level microorganisms. Correlation analysis revealed that there was no direct interaction between the differentical microorganisms at speices level and the host mucosal genes which regulating the production of intestinal SIgA (P>0.05), but Sutterella sp., Clostridium sp. CAG:138, Clostridium sp. CAG:762 and Nitrospira sp. were significantly positively correlated with serum IgG. Moreover, Clostridium sp. CAG:138 and Nitrospira sp. were significantly positively correlated with colonic mucosal SIgA. Finally, KEGG functional analysis found that the relative abundance of the intestinal immune network for IgA production in the 14% WBR group was significantly higher than that of the Basal group (P<0.05). In summary, replacing part of the basal diet with wheat bran could reduce the inflammatory level, enhance humoral immunity and promote the health of the colon of Meishan pigs, and the beneficial effect of 14% wheat bran replaced basal diet on Meishan pigs is better than that on Large White pigs. In addition, this study also found that the effects of dietary fiber on colonic mucosal SIgA of Meishan pigs may be through up-regulating the expression of CD4 and CCR9 genes in the colonic mucosa, and affecting the composition of intestinal microorganisms, thus enhancing the functional pathway of intestinal immune network for IgA production, improving intestinal barrier function and promoting body health.

Key words: wheat bran, pig, immunity, microorganism

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