Characterization of Holstein and Normande whole milk miRNomes highlights breed specificities.

The concept of milk as a healthy food has opened the way for studies on milk components, from nutrients to microRNAs, molecules with broad regulatory properties present in large quantities in milk. Characterization of these components has been performed in several species, such as humans and bovine, depending on the stages of lactation. Here, we have studied the variation in milk microRNA composition according to genetic background. Using high throughput sequencing, we have characterized and compared the milk miRNomes of Holstein and Normande cattle, dairy breeds with distinct milk production features, in order to highlight microRNAs that are essential for regulation of the lactation process. In Holstein and Normande milk, 2,038 and 2,030 microRNAs were identified, respectively, with 1,771 common microRNAs, of which 1,049 were annotated and 722 were predicted. The comparison of the milk miRNomes of two breeds allowed to highlight 182 microRNAs displaying significant differences in the abundance. They are involved in the regulation of lipid metabolism and mammary morphogenesis and development, which affects lactation. Our results provide new insights into the regulation of molecular mechanisms involved in milk production.