Extracellular vesicles miRNome during subclinical mastitis in dairy cows

Abstract Bovine mastitis is one of the main inflammatory diseases that can affect the udder during lactation. Somatic cell count and sometimes microbiological tests are routinely adopted during monitoring diagnostics in dairy herds. However, subclinical mastitis is challenging to be identified, reducing the possibilities of early treatments. The main aim of this study was to investigate the miRNome profile of extracellular vesicles isolated in milk as potential biomarkers of subclinical mastitis. Milk samples were collected from a total of 60 dairy cows during routine monitoring tests. Therefore, a smallRNA-sequencing technology was applied to extracellular vesicles of milk samples collected from cows classified according to the somatic cell count, in order to identify differences in the miRNome between mastitic and healthy cows. A total of 1,997 miRNAs were differentially expressed between groups. Among them, 68 miRNAs were obtained with FDR < 0.05, mostly downregulated and with only one upregulated miRNA (i.e., miR -361). Functional analysis revealed that miR -455-3p, miR -503-3p, miR -1301-3p and miR -361-5p were involved in the regulation of several biological processes related to mastitis, including immune system related processes. This study confirmed a strong involvement of extracellular vesicles-derived miRNAs in the regulation of mastitis. Moreover, it provides evidence that miRNA from milk extracellular vesicles can be used to identify biomarkers of mastitis. However, further studies must be conducted to validate those miRNAs, especially for subclinical diagnosis.