Gastrointestinal Microorganisms and Blood Metabolites in Holstein Calves with Different Heat Stress Responses in the Same Hot Environment.

This study investigated differences in gastrointestinal microbiota and blood metabolomes in calves with different heat stress (HS) responses in the same hot environment. Ten high (H) and ten low (L) HS response preweaning Holstein calves were selected based on their heat stress level (respiratory rate and rectal temperature), jugular vein blood samples and ruminal and fecal samples were collected. Notable variations were observed in the serum levels of heat shock protein 70 (HSP-70) and IL-2 between the two calf groups ( < 0.05). In group H, rumen and fecal microbiota synergism was disrupted. In the H group, the host metabolome exhibited enrichment in pyruvate metabolism and the tricarboxylic acid cycle ( < 0.05). Key factors bridging the relationship between gastrointestinal microbiota and serum metabolites included the rumen bacterial genus , serum HSP-70, malic acid, and fumaric acid. These hubs served as potential indicators for distinguishing the response to heat stress in calves ( < 0.05). In conclusion, this study identified the relationship between gastrointestinal microbiota characteristics and different HS responses of the host, thus providing evidence and new directions for future studies aimed at understanding HS in individual calves (gut microbiota-host interactions).