IntroductionAn injured tendon or ligament could be considered a career-ending injury to a show or working horse, improvements in regenerative medicine have made it possible for these horses to heal from these injuries. Regenerative medicine is defined by the United States Department of Health & Human Services as “the process of creating living, functional tissue to repair or replace tissue or organ functions due to age, disease, damage or congenital defects”(UC Davis Center for Equine Health Horse Report). One of the popular and still developing therapy for these kinds of injuries is stem cell therapy. This therapy uses stem cells for their self-regenerative capabilities to heal injuries. Various research has shown stem cell therapy reduces inflammation and helps speed the healing process of injured tendons and ligaments. As a developing therapy in equestrienne medicine, veterinarian uses different techniques as to how they harvest and use stem cells.What Are Stem Cells? Stem cells can be defined as unspecified cells in both human and horse body and can also be referred or as ” mother” cell. These cells have the ability to self-regenerate and differentiate into various cells or tissues. There are two types of stem cells, embryonic stem as adult stem cells. Embryonic cells have the capability of becoming any cell type or tissue in the body (Koch 2). Adult stem cells, on the other hand, are more limited. These cells are also divided into two groups hematopoietic and mesenchymal. The first type is hematopoietic stem cells which can become the various type of blood components like red blood cells, are typically found in bone marrow (Koch 2). The second type, Mesenchymal stem cells, can turn into the connective tissue to regenerate and heal tissue and are found in the umbilical cord, blood, tissue and bone marrow.Due to their wide availability and ability to regenerate and heal tissues, mesenchymal stem cells are used in commercial stem cell therapy.Stem Cell HarvestingIn early research, embryonic cells were used but due to its controversial harvesting method, this practice is not widely used. Embryonic stem cells were harvested from embryos, destroying them in the process making this source for stem cells controversial because of ethical considerations (Caudill 2).Therefore, active research was developed to obtain sources of stem cells. Currently, the stem cells used for therapy primary are derived from adipose and bone marrow. Adipose tissue, also known as fat, is used because it is readily available and can be collected in large quantities. In order to harvest this tissue, the horse is given mild sedation and the area next to the trailhead is blocked using local anesthetics (South Shore Equine Clinic & Diagnostic Center). Then, the vet proceeds to make a small vertical incision is made and the skin is undermined to expose adipose tissue (South Shore Equine Clinic & Diagnostic Center). The fat is harvested and collected in tubes for processing.These fat are shipped to a commercial laboratory where it is processed for increased tissue propagation. (Loving 1).Some issues that occur with harvesting adipose is that it can be problematic obtaining an adequate amount of fat in a young and fit racehorse.To obtain bone marrow fluid, veterinarians typically extracted from the horse’s sternum or ilium (hip bone). This process is done on standing horses using local anesthesia bone marrow aspiration needle is used to puncture and retrieve bone marrow. The bone marrow is then sent to the lab for processing and expansion. The expansion is necessary because the stem cells are diluted by the bone marrow blood making culture expansion necessary.As a result, it delays stem cell use for weeks. The last method of harvesting of this cells is maternally-derived stem cells. They derive from the umbilical cord blood as well as the tissue. Use of stem cell for ligament injuriesStem Cell therapy is still in its infancy stages, and much research is still occurring. As of now, stem cells have been used for tendon and ligament injuries, as they are the most common disorders in performance horses. Research conducted by UC Davis on tendonitis of the superficial digital flexor tendon or “bowed tendon, has shown a lower recurrence rate of bowed tendons in racehorses treated with stem cells compared to traditional therapies (UC Davis Center for Equine Health Horse Report). Other studies have shown that when stem cells are transplanted into a tendon or ligament injury, tissue regeneration access thru two different mechanisms. The first mechanism is by directly by differentiation into various tissues specific cell types. The second mechanism is indirectly contributes to the production of protein.The production of protein helps to reduce inflammation, stop cell death and assist tissue growth and healing (Loving 1). Both mechanisms can occur separately or simultaneous. Researchers believe that the anti-inflammatory effects and increased cells can help diminish the disruption of degenerative tendon fibers in the injury ( Loving 1). Also, stem cell transplant, improve the blood supply within the injury. As stated by researchers, the effect of stem cells on injuries is to maintain or induce organized tendon architecture, then increasing blood cells to help heal (Loving 1). Another study reviewed by Vet-Stem, evaluated 66 horses return to athletic function after treatment with adipose-derived stem cell therapy. The results showed that 84% of horses with chronic tendon injuries lasting longer than 3 months returns to full work (Vet Stem). Of the horses with acute injuries, 73% were able to get back to their previous athletic performance (Vet-Stem). On the other hand, horses with tendonitis lesions treated with conventional therapies, only 40 to 60% of them returned to soundness after one year. (Vet-Stem). The researchers took it a step further by treating suspensory ligament injury, which has proven to be difficult to resolve with conventional therapy (Vet-Stem). They found that horses treated with adipose-derived stem cells, 92% returned to their previous performance level (Vet-Stem). Although these results demonstrate the benefits of using stem cell therapy on injuries. Researchers warn owners that an injury can still take six to 12 months of rehabilitation even with the use stem therapy. Stem cell treatment has not yet proven to necessarily speed the healing process. ConclusionStem Cell therapy is still developing a method of regenerative medicine that uses a horse’s stem cells to help heal and reduce inflammation of injured ligaments or tendons.Studies have demonstrated the benefits of using this new and developing therapy to heal horses injuries. As a developing therapy, improvement to harvesting of stem cells are still being made and research is being conducted as to what stem cells to use for what injuries.Although research has demonstrated the positive effect of adipose-derived stem cell therapy, it has yet to prove it speeds up the healing process. However, Stem cell research offers horses with difficult tendon injuries the ability to return to their previous performance level.