Ggraphene oxide loaded with nano-ZnO alters gut microbiota community to promote secondary bile acid synthesis and immunity response in fattening cattle
Authors: Zhang Haibo , Guan Weikun , Li Lizhi , Guo Dongsheng , Xing Qingfeng , Huang Chaoyong , Xiong Chuanshuai , Li Baofeng , Chen Ketian , Peng Cong 
Published: April 2022

Abstract
Background
To our knowledge, graphene oxide loaded with nano-ZnO (NZnOGO) represent a new nutritional additive for the food and animal husbandry industry. However, the mechanism by which NZnOGO mediates cattle growth and intestinal health are not fully understood. This study was conducted to evaluate the effects of NZnOGO on gut microbiota, bile acid (BA) concentration and intestinal immunity in fattening cattle.
Results
Twenty Simmental × Chinese Yellow Cattle were assigned to 2 dietary groups: control diet (CON) without Zn supplement and CON diet supplemented with NZnOGO. The trial lasted 60 d. The gut microbiota composition and BA concentration in the colon chyme samples were determined by microbiota metagenomics and gas chromatography methods, respectively. Colon mucosa immune factors and gene expression analysis were determined by ELISA and RT-PCR, respectively. The results showed that dietary NZnOGO supplementation significantly increased average daily gain (P < 0.05), and significantly decreased feed conversion ratio (P < 0.05). The relative abundance of the secondary BA synthesis microbiota genera Clostridium, Ruminococcus, Eubacterium, Enterococcus, Collinsella, Fusobacterium, Eggerthella, Brevibacillus and Peptostreptococcus in the NZnOGO group had significantly higher than the CON group (P < 0.05). At the secondary BA synthesis pathway, NZnOGO group had significantly higher 7α-hydroxysteroid dehydrogenase (EC:1.1.1.159) and bile acid-CoA ligase BaiB (EC:6.2.1.7) than the CON group (P < 0.05). Dietary NZnOGO supplementation significantly decreased primary BA (taurocholic acid, taurochenodeoxycholic acid and taurodeoxycholate acid) (P < 0.05), and significantly increased secondary BA (deoxycholic acid, beta-Muricholic acid, 12-ketolithocholic acid, hyodeoxycholic acid, lithocholic acid, isolithocholic acid, ursodeoxycholic acid and apocholic acid) (P < 0.05). The NZnOGO group significantly increased the abundance of gene expression at metabolism and higher defense mechanisms (P < 0.05). The expression of Takeda G-protein-coupled receptor 5, protein kinase A, cyclic-AMP response element binding protein, toll-like receptor 4 and interleukin-10 (IL-10) genes were increased by dietary NZnOGO supplementation (P < 0.05), while the expression of nuclear factor kappa-B (NF-κB), tumor necrosis factor-α (TNF-α) and IL-1β genes were significantly decreased (P < 0.05). IL-10 concentration was increased by dietary NZnOGO supplementation (P < 0.05), whereas TNF-α and IL-1β contents were significantly decreased (P < 0.05).
Conclusions
Taken together, dietary NZnOGO supplementation improved the growth performance and intestinal immune function of the fattening cattle, compared to the diet free of Zn supplement, which was associated with enhancing secondary BA synthesis microbiota growth and promoting secondary BA synthesis.