Identification and comparison of exosomal microRNAs in the milk and colostrum of two different cow breeds

Bovine milk and colostrum provide essential nutrients and immunologically active factors that are beneficial to a newborn calf. Milk-and-colostrum-derived exosomes are known as the most important for cellular communication. Exosomes also contain non-coding RNA, such as microRNA. However, there is limited information about exosomal miRNA derived from the milk and colostrum of Holstein and DAK cattle. This study aimed to identify and characterize the exosomal microRNA in the milk and colostrum of Holstein and Dogu Anadolu Kirmizisi (DAK) cows. For this purpose, total RNA isolation was carried out on the milk and colostrum samples that were collected from the Holstein and DAK cattle breeds. The RNA samples were subjected to RNA sequencing and the microRNAs were determined. Lastly, gene ontology analysis was performed for target genes. A total of 795 miRNAs that were expressed differently were identified. A total of 545 of these were known miRNAs and 260 were found to be novel miRNAs. In the functional enrichment analysis, the miRNAs expressed in Holstein milk were mostly associated with milk synthesis, and those in colostrum were mostly involved in the immunity pathways. It was also observed that the miRNAs expressed in DAK milk regulated milk fat and protein metabolism, and there were miRNAs that regulated immune pathways in the colostrum. In addition to this, many novel miRNAs were defined in DAK colostrum. When the target genes of exosomal miRNA in Holstein and DAK milk and colostrum were compared, it was suggested that the DAK breed had genes that were mostly associated with the immune system. As a result, the data obtained from this study will provide beneficial contributions to potential miRNA biomarker studies for milk yield and mastitis.