Metagenomic Insights into Effects of Thiamine Supplementation on Carbohydrate-Active Enzymes’ Profile in Dairy Cows Fed High-Concentrate Diets

SIMPLE SUMMARY: Overfeeding a high-grain diet is known to reduce ruminal pH and microbial activity, disrupt carbohydrate metabolism, and consequently lead to subacute ruminal acidosis. Thiamine, as the co-enzyme of pyruvate formate-lyase, plays a critical role in carbohydrate metabolism in dairy cows. Therefore, we investigated the impacts of thiamine supplementation on ruminal carbohydrate-active enzymes using the metagenomic sequencing technique in lactating dairy cows fed high-concentrate diets. The results indicated that feeding high concentrate diets reduced fiber-degrading enzymes and the total carbohydrate-active enzymes. However, dietary thiamine supplementation increased fiber-degrading enzymes, starch-degrading enzymes, and total carbohydrate-active enzymes. These findings demonstrated that thiamine supplementation could enhance rumen carbohydrate metabolism through increasing the abundance of ruminal carbohydrate-active enzymes, providing effective strategies to improve dairy cows’ health and wellbeing under a high-concentrate feeding regime. ABSTRACT: As the co-enzyme of pyruvate formate-lyase under ruminal anaerobic condition, thiamine plays a critical role in carbohydrate metabolism in dairy cows. The objective of this study was to investigate the impacts of thiamine supplementation on ruminal carbohydrate-active enzymes. Twelve Holstein dairy cows were randomly assigned into three dietary treatments: control diet (CON; 20% starch, dry matter (DM) basis), high-concentrate diet (HC; 33.2% starch, DM basis) and a high-concentrate diet supplemented with 180 mg thiamine/kg DM (HCT; 33.2% starch, DM basis). Dry matter intake and milk production were recorded for 21 days. Rumen fluid samples were collected, and ruminal pH and volatile fatty acids (VFAs) were measured. The metagenome sequencing technique was used to detect the genes in ruminal microorganisms and identify putative carbohydrate-active enzymes. The total abundances of carbohydrate-active enzymes and fiber-degrading enzymes were both reduced by HC with no effect on starch-degrading enzymes compared with CON. However, the fiber-degrading enzymes and starch-degrading enzymes were both increased after thiamine supplementation. These results indicated that 180 mg thiamine /kg DM might effectively improve rumen carbohydrate metabolism through increasing the abundance of ruminal carbohydrate-active enzymes and consequently balanced the rumen volatile fatty acids and rumen pH, providing a practical strategy in preventing subacute ruminal acidosis in cows offered HC.