Changes in Rumen Epithelial Morphology and Transcriptome, Rumen Metabolome, and Blood Biochemical Parameters in Lactating Dairy Cows with Subacute Rumen Acidosis Following Rumen Content Transplantation.

Interventions targeting the gut microbiota, such as fecal microbiota transplantation, prove effective in repairing the intestinal barrier and facilitating the recovery of its function and metabolism. However, the regulatory mechanisms governing the remodeling of rumen epithelial morphology and function, rumen metabolism, and host metabolism in cows of subacute ruminal acidosis (SARA) remain poorly understood. Here, we explored the changes in rumen epithelial morphology and transcriptome, rumen metabolome, and blood biochemical parameters in SARA cows following rumen content transplantation (RCT). The entire experiment consisted of 2 periods: the SARA induction period and the RCT period. During the SARA induction period, 12 ruminally cannulated lactating Holstein cows were randomly allocated into 2 groups, fed either a conventional diet [CON; n = 4; 40% concentrate, dry matter (DM) basis] or a high-grain diet (HG; n = 8; 60% concentrate, DM basis). Following the SARA induction period, the RCT period started. The HG cows were randomly assigned to 2 groups: the donor-recipient (DR) group and the self-recipient (SR) group. Rumen contents were entirely removed from both groups before RCT. For the DR group, cows were administered 70% rumen content from the CON cows, paired based on comparable body weight; for the SR group, each cow received 70% self-derived rumen content. The results revealed no significant differences in the thicknesses of the stratum corneum, granulosum, and spinosum/basale layers, as well as the total depth of the epithelium between the SR and DR groups. All these measurements exhibited a decreasing trend and fluctuations over time after the transfer. Notably, these fluctuations tended to stabilize at 13 or 16 d after RCT in the SR group, whereas they tended to stabilize after 8 or 13 d of transfer for the DR group. Transcriptome sequencing revealed that a total of 277 differentially expressed genes (DEGs) were identified between the 2 groups. Enrichment analysis showed that the DEGs were significantly enriched in 11 Gene Ontology biological processes and 14 KEGG pathways. The DEGs corresponding to almost any of these 11 biological process terms and 14 pathways showed mixed up- or downregulation following RCT. Metabolomics analysis indicated that a total of 33 differential metabolites were detected between the SR and DR groups, mainly enriched in 5 key metabolic pathways, including plant polysaccharides and starch degradation, lipid metabolism, amino sugar and nucleotide metabolism, purine metabolism, and Krebs cycle. Among them, the levels of differential metabolites associated with the degradation of plant polysaccharides and starches, metabolism of amino sugars and nucleotides, and purine metabolism pathways were significantly elevated in the DR cows. The results of blood biochemical parameters showed that the triglyceride concentration of the DR cows was increased than that of the SR cows, comparable to the level observed in the CON cows during the SARA induction period. Generally, our findings indicated that RCT facilitated the recovery of rumen epithelial morphological structure but did not promote its function recovery. Moreover, RCT enhanced rumen plant polysaccharide and starch degradation, amino sugar and nucleotide sugar metabolism, as well as purine metabolism. Additionally, it further promoted the recovery of plasma metabolites related to lipid metabolism.

Gene function adjustment for carbohydrate metabolism and enrichment of rumen microbiota with antibiotic resistance genes during subacute rumen acidosis induced by a high-grain diet in lactating dairy cows.

The high-grain diets fed to ruminants generally alters the structure and function of rumen microbiota, resulting in variations of rumen fermentation patterns and the occurrence of subacute rumen acidosis (SARA). To clarify the microbial mechanism for carbohydrate metabolism during SARA, 8 ruminally cannulated Holstein cows in mid lactation were selected for a 3-wk experiment. The cows were randomly divided into 2 groups, fed either a conventional diet (CON; 40% concentrate; dry matter basis) or a high-grain diet (HG; 60% concentrate; dry matter basis). Compared with the CON diet, the HG diet reduced average daily pH (5.71 vs. 6.13), acetate concentration (72.56 vs. 78.44 mM), acetate ratio (54.81 vs. 65.24%), and the ratio of the concentrations of acetate to propionate (1.87 vs. 3.21) but increased the concentrations of total volatile fatty acids (133.03 vs. 120.22 mM), propionate (41.32 vs. 24.71 mM), and valerate (2.46 vs. 1.68 mM) and the propionate ratio (30.51 vs. 20.47%). Taxonomic analysis indicated that the HG cows had a higher relative abundance of Ruminococcus, Eubacterium, Selenomonas, Ruminobacter, Succinimonas, Methanomicrobium, and Methanocaldococcus accompanied by a lower relative abundance of unclassified Firmicutes, unclassified Bacteroidetes, Bacteroides, Fibrobacter, Alistipes, Candidatus Methanoplasma, Methanomassiliicoccus, and Methanolobus. Carbohydrate-active enzyme annotation suggested that there was enriched abundance of glycosyltransferases (GT) 2, glycoside hydrolase (GH) 13, GH24, carbohydrate-binding module (CBM) 26, GH73, GH25, CBM12, GH23, GT8, CBM50, and GT9 and reduced abundance of GH78, GH31, S-layer homology, GH109, carbohydrate esterase 1, GH3, carbohydrate esterase 10, and GH43 in the HG group. Functional profiling revealed that the HG feeding mainly downregulated the pentose phosphate pathway of carbohydrate catabolism, acetate metabolism, propionate metabolism (succinate pathway), and methane metabolism, whereas it upregulated the Embden-Meyerhof-Parnas and Entner-Doudoroff pathways of glycolysis and the citrate cycle. Additionally, the HG feeding promoted the abundance of various antibiotic resistance genes and antimicrobial resistance gene families. These results elucidated the structure and function adjustment of rumen microbiota for carbohydrate metabolism and summarized the enrichment of rumen antibiotic resistance genes under the HG feeding, which expands our understanding of the mechanism underlying the response of rumen microbiota to SARA in dairy cattle.

Changes in rumen fermentation and bacterial community in lactating dairy cows with subacute rumen acidosis following rumen content transplantation.

Rumen microbiota intervention has long been used to cure ruminal indigestion in production and has recently become a research hotspot. However, how it controls the remodeling of rumen bacterial homeostasis and the restoration of rumen fermentation in cows of subacute ruminal acidosis (SARA) remains poorly understood. This study explored changes in rumen fermentation and bacterial communities in SARA cows following rumen content transplantation (RCT). The entire experiment comprised 2 periods: the SARA induction period and the RCT period. During the SARA induction period, 12 ruminally cannulated lactating Holstein cows were selected and allocated into 2 groups at random, fed either a conventional diet [CON; n = 4; 40% concentrate, dry matter (DM) basis] or a high-grain diet (HG; n = 8; 60% concentrate, DM basis). After the SARA induction period, the RCT period began. The HG cows were randomly divided into 2 groups: the donor-recipient (DR) group and the self-recipient (SR) group, and their rumen contents were removed completely before RCT. For the DR group, cows received 70% rumen content from the CON cows, paired based on comparable body weight; for the SR group, each cow received 70% rumen content, self-derived. The results showed that nearly all rumen fermentation parameters returned to the normal levels that the cows had before SARA induction after 6 d of transplantation, regardless of RCT. The concentrations of acetate, valerate, and total volatile fatty acids (VFA) were not recovered in the SR cows, whereas all of them were recovered in the DR cows. The amplicon sequencing results indicated that both the SR and DR cows rebuild their rumen bacterial homeostasis quickly within 4 d after RCT, and the DR group showed a higher level of bacterial community diversity. At the genus level, the DR cows displayed an improved proportion of unclassified Ruminococcaceae and Saccharofermentans compared with the SR cows. Correlation analysis between the rumen bacteria and rumen fermentation suggested some potential relationships between the predominant transplantation-sensitive operational taxonomic units and VFA. Co-occurrence network analysis revealed that RCT affected only those rumen bacterial taxa that showed weak interactions with other taxa and did not affect the pivotal rumen bacteria with high levels of co-occurrence. Our findings indicate that RCT contributes to the restoration of rumen bacterial homeostasis and rumen fermentation in cows suffering from SARA without affecting the core microbiome.