L. C. Berg, T. G. Koch, T. Heerkens, K. Bessonov, P. D. Thomsen, D. H. Betts Veterinary and Comparative Orthopaedics and Traumatology 2009 5 363-370 Objective: Orthopaedic injury is the most common cause of lost training days or premature retirement in the equine athlete. Cell-based therapies are a potential new treatment option in musculo-skeletal diseases. Mesenchymal stromal cells (MSC) have been derived from multiple sources in the horse including bone marrow and umbilical cord blood. The objective of this study was to provide an in vitro comparison of the chondrogenic potential in MSC derived from adult bone marrow (BM-MSC) and umbilical cord blood (CB-MSC). Results: MSC from both sources produced tissue with cartilage-like morphology that stained positive for proteoglycans and expressed cartilage markers. The CB-MSC pellets were larger and showed hyaline-like cartilage morphology as early as day six. Gene expression of collagen type 21, aggrecan and CD-RAP was higher in CB- than BM-MSC pellets. Expression of Sox9 mRNA was similar between CB- and BM-MSC pellets. Protein concentration of cartilage-derived retinoic acid sensitive protein was higher in culture medium from CB- than BM-MSC pellets. Conclusion: CB-MSC and BM-MSC were both capable of producing hyaline-like cartilage in vitro . However, in this study the MSC from umbilical cord blood appeared to have more chondrogenic potential than the BM-MSC based on the cells tested and parameters measured.