Dairy cattle are frequently fed high-concentrate (HC) diets in modern intensive feeding systems, especially in the transition period. During this period, cows face many alterations that include hormonal changes and shifting to a lactating state. Switching to a HC diet that may disrupt the ruminal microbiota balance can lead to subacute ruminal acidosis (SARA). Moreover, the main factor shaping the rumen microbiota is dietary composition, especially the ratio of starch to fibrous carbohydrates. Feeding highly fermentable carbohydrate diets after adaptation to forage diets leads to a rumen fermentation rate that exceeds rumen absorption and buffering rates, resulting in a reduction in ruminal pH. As a result of Gram-negative bacterial cell lysis, an increase in harmful ruminal bacterial metabolites, including lipopolysaccharide, lactic acid, and histamine, is observed. The interactions between the host immune system and the ruminal microbiota play an essential role in many physiological processes and the development of the disorder. Progress in DNA sequencing and bioinformatics platforms provides new opportunities to investigate the composition of ruminal microbes and yields unique advances in understanding ecology of the rumen. Subacute ruminal acidosis is linked with a change in the ruminal microbiota structure and richness and with other metabolic disorders; such as rumenitis, milk fat depression, laminitis, and liver abscesses. Therefore, this review aims to explore a better understanding of the crosstalk between diet and microbiota in the prevalence of rumen acidosis and its consequences, which is crucial for control strategies such as feeding management, and supplementation with thiamine, prebiotics, and probiotics.

Data indicate that dietary thiamine supplementation can partly alleviate rumen epithelium inflammation and barrier function in goats fed a high-concentrate diet. The current work aimed to explore whether thiamine promotes rumen epithelium development by regulating carbohydrate metabolism during a long period of feeding high levels of concentrate. For the experiment, 24 female Boer goats (35.62 ± 2.4 kg of body weight) in parity 1 or 2 were allocated to 3 groups (8 goats per replicate) receiving a low-concentrate diet (concentrate:forage 30:70), a high-concentrate diet (HC; concentrate:forage 70:30), or a high-concentrate diet (concentrate:forage 70:30) supplemented with 200 mg of thiamine/kg of dry matter intake (HCT; concentrate:forage 70:30). On the last day of 12 wk, rumen fluid and blood samples were collected to measure ruminal parameters, endotoxin lipopolysaccharide, and blood inflammatory cytokines. Goats were slaughtered to collect ruminal tissue to determine differential metabolites, enzyme activities, and gene expression. Liquid chromatography-tandem mass spectrometry analysis revealed that the HCT group had significantly increased concentrations of d-glucose 6-phosphate, d-fructose 6-phosphate, glyceraldehyde 3-phosphate, thiamine pyrophosphate, oxaloacetate, acetyl-CoA, succinyl-CoA, sedoheptulose 7-phosphate, ribose 5-phosphate, and NADPH compared with the HC group. The pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase enzyme activities in the rumen epithelium of the HCT group were higher than those in the HC group. The plasma total antioxidant capacity values for the HCT group were greater than those for the HC group. The rumen epithelium ATP content in the HCT group was higher than that in the HC group. Compared with the HCT group, the HC group had a lower mRNA abundance of CCND1, CCNA2, CDK2, CDK4, CDK6, BCL2, PI3K, and AKT1. Taken together, the results suggest that dietary thiamine supplementation could ameliorate disorders in the tricarboxylic acid cycle and the pentose phosphate pathway induced by a long-term high-concentrate diet and could promote rumen epithelial growth.

Studies have shown that exogenous thiamine (THI) supplementation can alleviate inflammation and promote rumen epithelial development in goats and cows. This research aimed to evaluate the effect of THI supplementation on LPS-induced inflammation and energy metabolic dysregulation in RECs of goats. Cells were stimulated with either 5 μg/mL THI for 18 h (THI group) or with 5 μg/mL LPS for 6 h (LPS group). The CON group was stimulated with DMEM/F-12 medium without THI for 18 h. The LPTH group was pretreated with THI for 18 h, followed by LPS stimulation for 6 h. THI supplementation decreased the ROS content (p < 0.05), as well as the ratios of phosphorylated (p)-p65 to p65 (p < 0.05) and p-AMPKα to AMPKα (p < 0.05). Interestingly, when the p38 gene was overexpressed in the LPTH group, the ratio of p-p65 to p65 and p-AMPKα to AMPKα proteins significantly increased, and ATP content decreased (p < 0.05). Our results suggest that THI possesses anti-inflammatory and metabolic-modulatory effects in RECs. The mechanism is largely related to the suppression of the NF-κB/p38 MAPK/AMPK signaling pathway. Additionally, we also revealed that THI supplementation can inhibit LPS-induced oxidative damage and apoptosis to protect mitochondrial function in RECs.

This study investigated the effects of tannic acid (TA)-treated corn on changes in ruminal fermentation characteristics and the composition of the ruminal bacterial community in vitro. Ruminal fluid was obtained from three rumen-fistulated goats fed a 60:40 (forage/concentrate) diet. The batch cultures consisted of 25 ml of strained rumen fluid in 25 ml of an anaerobic buffer containing 0.56 g of ground corn, 0.24 g of soybean meal, 0.10 g of alfalfa, and 0.10 g of oat grass. Ground corn (2 mm) was steeped in an equal quantity (i.e., in a ratio of 1:1, w/v) of water alone (Con), 15 (TA15), 25 (TA25), and 35 g/l (TA35) TA solution for 12 h. After incubation for 24 h, TA-treated corn linearly increased (P <0.05) ruminal pH and the molar proportion of acetate, but linearly reduced (P <0.05) total volatile fatty acids and the molar proportion of butyrate compared with the Con treatment. Illumina MiSeq sequencing was used to investigate the profile changes of the ruminal microbes. A principal coordinates analysis plot based on weighted UniFrac values revealed that the structure of the ruminal bacterial communities in the control group was different from that of the TA-treated corn groups. The results of changes in the rumen bacterial communities showed that TA-treated corn linearly enriched (P <0.05) Rikenellaceae_RC9_gut_group, but linearly reduced (P <0.05) Ruminococcaceae_NK4A214_group, Ruminococcus_2, and unclassified_o__Clostridiales. Functional prediction of ruminal microbiota revealed that the TA-treated corn linearly decreased ruminal microbiota function of utilizing starch through pyruvate metabolism. In conclusion, TA-treated corn can modulate the rumen fermentation characteristics, microbial composition, and metabolic pathways, which may be potentially useful for preventing the occurrence of ruminal acidosis.

Several studies have demonstrated that high-concentrate (HC) diet with thiamine supplementation can alleviate rumen epithelium inflammation and protecting the barrier function in goats. This study aimed to investigate the effects of dietary supply of thiamine on mitophagy and endoplasmic reticulum stress (ERS) during high-concentrate diet feeding. Twenty-four Boer goats (35.62 ± 2.4 kg) were used in this study, goats were subsequently assigned to 3 treatment groups (8 goats in each group) as follows: a low-concentrate diet (CON; concentrate: forage 30:70), a high-concentrate diet (HC; concentrate: forage 70:30) and high-concentrate diet with 200 mg thiamine/kg DMI (HCT; concentrate: forage 70:30) for 12 weeks. Compared with the HC group, the goats of HCT group had a markedly higher final weight, net weight gain, and average daily gain (ADG). The blood physiological and biochemical results showed that the HCT group expressed a lower the content of lymphocytes and leukocytes but a higher total protein and monocytes compared with that of HC group. The rumen epithelial mitochondrial membrane potential change (ΔΨm), relative mitochondrial DNA (mtDNA) content, adenosine triphosphate (ATP) level, together with the activities of the respiratory complexes I, III, and IV were markedly higher in the HCT group relative to HC ones. Relative to the HC group, the unc-51 like autophagy activating kinase 1 (ULK1), microtubule-associated protein 1 light chain 3 (LC3), autophagy-related 5 (ATG5), autophagy related 7 (ATG7), Beclin1, PTEN induced putative kinase 1 (PINK1), PERK (PKR-Endoplasmic Reticulum Kinase), activating transcription factor 4 (ATF4), activating transcription factor 6 (ATF6), X-box binding protein 1 (XBP1), heat shock 70 kDa protein 5 (HSPA5), DNA damage-inducible transcript 3 (DDIT3) and DNA damage-inducible transcript 4 (DDIT4) mRNA levels were decreased, but the breast cancer 1 (BRCA1), ataxia telangiectasia mutated (ATM), heat shock factor binding protein 1 (HSBP1) were increased in rumen epithelium of the HCT group. The results of transmission electron micrographs showed that the cell structure of the HCT group was higher integrity than that in the HC group, and the damage degree of mitochondria as well as endoplasmic reticulum being lower than the HC group. These results demonstrated that dietary thiamine could enhance rumen epithelial integrity by suppressing the responses of ERS and mitophagy during long-term HC diet feeding.

Temperature is a fundamental regulator of microbial physiology, shaping processes from growth and respiration to community interactions and ecosystem functioning. This review synthesizes recent experimental and theoretical advances that reveal how microbes respond to warming across biological scales, with a focus on short-term ecological acclimations of microbial communities. At the cellular level, rising temperature affects enzyme kinetics, membrane fluidity, and metabolic efficiency, often in non-linear ways that challenge the validity of fixed Q ₁₀ -based models. At the community level, warming tends to favor thermotolerant and slow-growing taxa, while reconfiguring microbial interaction networks by shifting balances between competition, cooperation, and syntrophy. These structural changes can reduce functional redundancy and stability, yet prolonged warming may also foster the emergence of cohesive, resilient community architectures. Overall, we emphasize the need for integrative mechanistic frameworks that link thermal physiology, carbon-use efficiency, and microbial interactions to improve predictions of microbial contributions to carbon cycling under climate change.