Fecal microbiota and their association with heat stress in Bos taurus

Humans have been influencing climate changes by burning fossil fuels, farming livestock, and cutting down rainforests, which has led to global temperature rise. This problem of global warming affects animals by causing heat stress, which negatively affects their health, biological functions, and reproduction. On the molecular level, it has been proved that heat stress changes the expression level of genes and therefore causes changes in proteome and metabolome. The importance of a microbiome in many studies showed that it is considered as individuals "second genome". Physiological changes caused by heat stress may impact the microbiome composition. In this study, we identified fecal microbiota associated with heat stress that was quantified by three metrics - rectal temperature, drooling, and respiratory scores and represented by their Estimated Breeding Values. For this purpose, the 16S rRNA sequencing technique was used. We analyzed the microbiota from 136 fecal samples of Chinese Holstein cows through a 16S rRNA gene sequencing approach. Sequence data were processed using a pipeline involving QIIME2 software together with SILVA database. Statistical modeling was performed using a negative binomial regression. The analysis revealed the total number of 24 genera and 12 phyla associated with heat stress metrics. Rhizobium and Pseudobutyrivibrio turned out to be the most significant genera, while Acidobacteria and Gemmatimonadetes were the most significant phyla. Phylogenetic analysis revealed that that three heat stress indicators quantify different metabolic ways of animals reaction to heat stress. Other studies already identified that those genera had significantly increased abundance in mice exposed to stressor-induced changes. Moreover, identified microbiota significantly associated with heat stress measures were mostly mesophilic, so their association seems to be due to heat stress-induced secondary, metabolic changes, and not directly by temperature. Moreover, high fold changes of many genera suggest that they may be used as biomarkers for monitoring the level of heat stress in cattle.