This study focuses on a promising yet under investigated research area in equine regenerative medicine, namely the potential of the mesenchymal stem cell (MSC) secretome as an effective therapy for cutaneous wounds in horses. Skin wounds are very common in equine patients, causing a major financial impact on the equine industry. In the US, roughly 7% of all injuries leading to the retirement of racehorses are the direct result of serious wounds (Theoret & Wilmink, 2013). Overall, wound management represents a significant portion of the equine practitioner's workload and can be a challenging endeavor (Caston, 2012). Successful treatments for cutaneous wounds are urgently needed to maximize benefits and reduce suffering and expense.

The use of mesenchymal stem cells (MSC) in equine regenerative medicine has received increasing attention in recent years. MSC are commonly used in equine practice to treat musculoskeletal disorders like tendinitis, osteoarthritis and laminitis (Schnabel et al., 2013), but non-orthopedic clinical applications, including promoting wound healing, are also being explored (De Schauwer et al., 2013). Although the ‘mode of action’ of these cells remains poorly understood, secreted bioactive factors, defined as the stem cell secretome, are thought to play a critical role in explaining the clinically relevant functions of MSC (Lavoie & Rosu-Myles, 2013). The secretome offers advantages over traditional cellular MSC therapies in that it circumvents (i) rejection reactions by the recipient, (ii) the risk of tumor formation of donor MSC and (iii) ectopic tissue formation of donor MSC (Dimarino et al., 2013; Sutton& Bonfield, 2014; Hanson et al., 2014). These features make the MSC secretome an ideal candidate for clinical use, since there is no risk of recipient rejection of allogeneic cells or side-effects associated with inappropriate tissue growth. In addition, the MSC secretome is a naturally occurring mix of bioactive factors at safe, physiologic concentrations that are unlikely to induce negative effects due to toxicity. Interestingly, we recently found that the secretome of equine MSC, delivered through conditioned medium (CM), stimulates angiogenesis and increases the migration potential of equine dermal fibroblasts in vitro, two very important steps during wound healing (Bussche & Van de Walle, 2014; Bussche et al., 2015).