Changes in growth performance, serum biochemical parameters, rumen microbiota structure, and metabolism in yaks following rumen fluid- fermented roughage intervention

Background This study investigated the effects of rumen fluid-fermented roughage on the rumen microbiota and the growth performance of yaks. Twenty yaks with similar body conditions were randomly divided into two groups (n = 10 per group), and fed either a basal diet (CON) or 10% rumen fluid-fermented roughage. The experiment lasted 75 d, including a 15 d adaptation period and a 60 d treatment period. At the end of the experiment, serum and rumen fluid samples were collected and analyzed. The microbial communities and metabolomic profiles in the rumen fluid were analyzed using 16S rRNA sequencing and non-targeted metabolomics, respectively. Results Results showed a significant rise in serum alanine aminotransferase levels, while serum total protein and cholesterol concentrations decreased notably. Furthermore, rumen fluid ammonia nitrogen and acetic acid concentrations decreased significantly, while concentrations of yak rumen microbial protein, isovaleric acid, and valeric acid increased significantly. Rumen microbial diversity was enhanced, with decreased abundances of Firmicutes , Cyanobacteria , Klebsiella , Spirochaetota , fungi, and Pseudomonas , alongside increased populations of Anaeroplasma , Spirochaetota , Fibrobacter , and Succiniclasticum . Furthermore, the activity of the bile secretion pathway and concentrations of its metabolites—including deoxycholic acid, chenodeoxycholic acid, glycocholic acid, and glycodeoxycholic acid—were significantly elevated. Conclusions These findings indicate that rumen fluid-fermented coarse feed not only promotes yak growth but also enhances health by modulating metabolites associated with cellular proliferation, such as dUMP, adenylosuccinate, and DL-α-tocopherol. Consequently, rumen fluid-fermented coarse feed represents a beneficial dietary supplement for improving growth performance and overall health in yaks.