Characterizing Thiamine Status and Mechanisms of Thiamine Supplementation on Subacute Ruminal Acidosis Attenuation in Dairy Cows

Dairy cows are often fed high grain diets to maximize milk production in today’s intensive management farms. However, overfeeding high grain diets increases the risk of subacute ruminal acidosis (SARA), which is characterized by prolonged decrease in rumen pH and high levels of lipopolysaccharide (LPS). SARA challenge has been confirmed to severely impair animal health, production performance and farm profitability, and more and more attentions have been paid to prevent the occurrence of SARA in dairy industry worldwide. Our teams’ previous research found that thiamine supplementation relieved SARA in dairy cows, but the modes of action of thiamine in SARA attenuation are still unclear. In this context, this thesis was conducted to increase our understanding of relationships between SARA induction and thiamine, and to explore the mechanisms of thiamine supplementation on SARA attenuation by determining its effects on rumen fermentation, microbiome composition and anti-inflammatory response. Firstly, the first experiment in Chapter III demonstrated that thiamine status in rumen and blood were altered by SARA induction and thiamine deficiency occurred during SARA challenge. Regression analysis proved the ruminal thiamine content was positively related to pH and the concentrations of acetate in the rumen, and negatively correlated to the lactate contents, indicating the altered rumen fermentation would affect thiamine status. Secondly, the mRNA expression of thiamine transporters in ruminal epithelium (Chapter IV) and ruminal bacteria compositions (Chapter V) in SARA and control cows were detected. We found that thiamine concentration was positively correlated with Bacteroides, Ruminococcus 1, Ruminobacter, Pyramidobacter and Fibrobacter, and the decrease in these genera implied SARA challenge altered ruminal thiamine status by inhibiting the growth of thiamine synthesis related bacteria. The positive correlation between ruminal and blood thiamine, and the down-regulation of thiamine transporters’ expression in rumen epithelium indicated the reduced ruminal thiamine synthesis and thiamine absorption by SARA challenge resulted in low blood thiamine content of SARA cows. Thirdly, the effects of thiamine on rumen fermentation (Chapter III), anti-inflammatory response (Chapter IV) and microbiome composition (Chapter V) were evaluated to reveal its mechanisms on SARA attenuation. We found that thiamine supplementation promoted acetate-producing bacteria including Ruminococcus 1, Pyramidobacter, Succinivibrio and Bacteroides, and decreased bacteria positively related to ruminal lactate (Succiniclasticum and Ruminococcaceae NK4A214). Consequently, rumen fermentation was improved by reducing the accumulation of lactate and increasing ruminal pH. In addition, thiamine supplementation alleviated inflammatory response in rumen epithelium by reducing the release of LPS and phosphorylation of NFκB protein, which is conducive to SARA attenuation. In summary, this thesis had increased our understanding of thiamine nutrition in dairy cows, and provided a new control strategy for subacute ruminal acidosis in dairy cows. However, further investigations are needed to deeply understand the relationship between thiamine and SARA induction, such as the isolation and validation of thiamine synthesis bacteria affected by SARA challenge, as well as to figure out metabolic pathways through which SARA induction affects thiamine synthesis in the rumen. Moreover, the impacts of overfeeding high grain diets on intestinal thiamine absorption are still unclear and need to be illuminated in dairy cows.