**5. Isolation of MSCs from bone marrow**

The postnatal bone marrow (BM) has been the most studied tissue as a source of progenitor cells. It contains at least two cell populations: the hematopoietic stem cells (HSCs), located in proximity to the endosteum, and MSCs that surround the trabeculae and blood vessels [37]. HSCs are capable of regenerating the peripheral blood cell lines and the immune system, and the MSCs [38] are capable of giving rise to tissues of each of the three germ layers. Although MSCs derived from BM are easily separated from the nonadherent hematopoietic fraction of cells by culture and adherence to plastic dishes, BM harvest is an invasive and painful surgical procedure that requires the anesthesia and it could be associated with the risk of complications such as hemorrhage, infection, pneumothorax, or pneumopericardium in horses [39, 40]. Moreover, there is only a very low frequency (0.001–0.01%) of MSCs in bone marrow and these numbers decline with the age of the individual.
