Comparison of autogenous cancellous bone grafts obtained from the sternum and proximal portion of the tibia of llamas.

OBJECTIVE: To describe the anatomy of the sternum in llamas, define the surgical approach to the sternum for collection of cancellous bone graft tissue, and compare the histologic appearance of graft tissue obtained from the sternum with that obtained from the proximal portion of the tibia. DESIGN: Prospective study. ANIMALS: 12 llamas, 3 to 19 years old, that had been submitted for necropsy. PROCEDURE: Radiographs were taken of the sternum and left tibia of the llamas. Measurements of the sternum were determined from the radiographs and adjusted for magnification. Sternebrae volumes were estimated from these measurements. Anatomic dissections to the center of the fourth sternebra and the proximal portion of the tibia were made, and a surgical approach to the sternum was developed. Cancellous graft tissue was obtained from each site and submitted for histologic evaluation. RESULTS: Sternebrae 3, 4, and 5 were significantly larger in volume than the other sternebrae. The ventral aspect of the fourth sternebra was readily accessed for removal of graft tissue by making a 6-cm-long ventral midline incision centered 17 cm craniad to the xipnoid. Mean soft tissue thickness overlying the ventral aspect of the fourth sternebra was 3.1 cm. More tissue was obtained from the sternal (mean, 9.11 g) than from the tibial (mean, 5.16 g) sites. Sternal graft tissue consisted of trabecular bone spicules with predominantly hematopoietic marrow, whereas tibial tissue consisted of trabecular bone spicules with only fatty marrow. CONCLUSIONS AND CLINICAL RELEVANCE: The fourth sternebra in llamas is readily accessible for obtaining autogenous cancellous bone graft tissue that consists of predominantly hematopoietic marrow.     

Estudio Radiológico del Esternón del Ovino en Crecimiento

Radiological investigation of the sternum of the sheep A radiological investigation of the sternum of the sheep demonstrated distinct growth phases. Forty Merino sheep of mixed breeds were distributed into 4 age groups of 0, 45, 105 and 270 days. Each animal was radiographed in sternal and lateral recumbency. Measurements were made from the radiographs. The sternebra are rectangular in newborn and become concave in adult. The curvature of the sternum is 16 to 17° at day 0 and 27–28° at day 270. The nucleus of ossification was seen in all sternebrae at 45 days of age, they were present only in the most caudal sternebrae at 105 days.     

Autogenous Cancellous Bone Grafts From the Sternum in Horses Comparison With Other Donor Sites and Results of Use in Orthopedic Surgery

Cancellous bone was collected from the fourth or fifth sternebra of six horses aged 12 to 36 months, and compared quantitatively and qualitatively with cancellous bone collected from the tuber coxa, proximal tibia, and rib at the time of necropsy, 28 to 49 days after surgery. Cancellous bone collected from the sternum was equivalent in amount and in microscopic appearance to that collected from the other three sites.
Cancellous bone also was collected from the sternum for use during clinical orthopedic surgery in 18 horses. Wound dehiscence occurring in two horses healed uneventfully by second intention. In each horse, an adequate amount of cancellous bone was obtained from one sternebra, with the exception of one horse where cancellous bone from two sternebra was used. Major complications with the donor sites were not encountered.     

Sternal bone biopsy in standing horses

OBJECTIVE: To develop a technique for sternal bone biopsy in standing horses. STUDY DESIGN: Experimental study. ANIMALS: Five adult horses. METHODS: Horses were restrained in a standing stocks and sedated. The sternal biopsy site, identified by ultrasonographic examination, was clipped and prepared for aseptic surgery and infiltrated with local anesthetic. An electric bone biopsy drill (Osteocore; Institut Straumann AG, CH-4437, Waldenburg, Switzerland)), which yielded 4-mm-diameter bone specimens, was used to obtain sternal biopsies through a small skin incision. Sections (7 microm) of the bone specimens were stained with toluidine blue and Goldner's green trichrome and observed microscopically to determine suitability for histological and histomorphometric evaluation. RESULTS: The most suitable sternal biopsy site was at the 4th or 5th sternebra. The surgical procedure was easy to perform and well tolerated by the horses, and adequate samples were obtained on the first attempt. The only complications were incisional edema in all horses and wound drainage in 1 horse. CONCLUSIONS: Sternal bone biopsy may be successfully performed in standing horses, and the technique described in this report yields architecturally intact bone specimens. CLINICAL RELEVANCE: The sternum is an accessible site for cancellous bone biopsy specimens in standing horses.     

Comparison of bone marrow aspiration at the sternum and the tuber coxae in middle-aged horses

The objective of this study was to compare bone marrow (BM) aspirates from the sternum and the tuber coxae of middle-aged horses. Bone marrow was obtained from the sternum and both tubera coxae of 12 healthy, 13-year-old geldings. Two different puncture techniques were used for the tuber coxae. The 2 syringes used for sternal sampling were evaluated separately. The mononuclear cell (MNC) fraction of the BM was isolated and the mesenchymal stem cells (MSCs) were culture-expanded. At the sternum, BM aspiration was always possible. Bone marrow aspiration at the tuber coxae required straight and deep needle penetration combined with high negative pressure. With this technique a median sample amount of 11.0 mL with large individual variation was obtained. A median of 3.06 × 10(6) MNC/mL BM (1st syringe) and 2.46 × 10(6) MNC/mL BM (2nd syringe) was isolated from sternal samples. In contrast, the tuber coxae yielded a median of 0.27 × 10(6) MNC/mL BM. The first passage yielded a median of 2.19 × 10(6) MSC (1st syringe) and 1.13 × 10(6) MSC (2nd syringe) from sternal samples, compared to a significantly lower median number of MSC from tuber coxae BM (0.06 × 10(6) MSC). The number of MNC and MSC obtainable from the BM aspirates taken from the tuber coxae is significantly lower than that obtained from the sternal BM aspirates. Autologous BM for the equine athlete is particularly clinically relevant at an advanced age. Based on our findings, the tuber coxae cannot be recommended for BM aspiration in middle-aged horses.     

Ultrasound‐guided lipoaspiration for mesenchymal stromal cell harvest in the horse

Mesenchymal stromal cells (MSC) are being used to treat a variety of conditions in the horse. Traditional lipectomy and bone marrow aspiration for MSC harvest have disadvantages including cosmetic issues with lipectomy and extensive time for cell expansion after bone marrow harvests. This article describes a new technique of adipose harvest in the horse, utilising ultrasound and liposuction that can be safely and effectively performed in an ambulatory environment. Ultrasound‐guided lipoaspiration offers a minimally invasive technique using small portals and a diffuse area of collection significantly improving aesthetic outcome and increasing the likelihood of treating within a matter of days vs. a matter of weeks.     

Open surgical correction combined with an external splint for correction of a non-compliant pectus excavatum in a cat

A 4-month-old domestic shorthair female cat weighing 1.3 kg was presented for evaluation of respiratory distress. The animal showed evident dyspnoea with exercise intolerance and a marked concave deformation of the sternum. After measurements of the fronto-sagittal and vertebral indexes, the pectus was classified as moderate and surgery was elected. Surgical correction was performed using an open approach to the sternum with osteotomy of the last sternebra and costochondral junctions of the eighth and ninth ribs bilaterally. A silicone based, U-shape external splint was manufactured and used to stabilise the sternum. Immediate and 5-week postsurgical radiographs revealed a decreased concavity of the sternum and an increase thoracic height at the level of the last sternebra. Postoperative results suggest that this technique could be an effective and economical option for cats with pectus excavatum with a non-compliant sternum.     

Scintigraphic evaluation of intra-arterial and intravenous regional limb perfusion of allogeneic bone marrow-derived mesenchymal stem cells in the normal equine distal limb using (99m) Tc-HMPAO

Reasons for performing study: Mesenchymal stem cells (MSCs) are commonly injected intralesionally for treatment of soft tissue injuries in the horse. Alternative routes of administration would be beneficial for treatment of lesions that cannot be accessed directly or to limit needle‐induced iatrogenic damage to the surrounding tissue. Objectives: The purpose of our study was to evaluate MSC distribution after intra‐arterial (IA) and intravenous (IV) regional limb perfusions (RLP) using scintigraphy. We hypothesised that MSCs would persist in the distal limb after tourniquet removal and that both techniques would lead to diffuse MSC distribution. Methods: Six horses were used in the study. MSCs were labelled with hexamethyl propylene amine oxime (HMPAO) and technetium‐99m. RLP was performed through the median artery of one forelimb and the cephalic vein of the opposite limb under general anaesthesia. The tourniquet was left in place for 45 min. Scintigraphic images were obtained at 0, 45, 75 min, 6 h and 24 h post injection. Results: Distribution of labelled MSCs through the entire distal limb was achieved with all 6 IA RLP, but 3 out of 6 IV RLP showed poor or absent uptake distal to the metacarpus. Mesenchymal stem cell persistence was 39% (30–60%) and 28% (14–50%) (median [minimum–maximum]) at 6 h for IA and IV RLP, respectively. Severe arterial thrombosis occurred in one horse after IA RLP. Conclusions: Both IA and IV RLP of the distal limb result in MSC persistence in perfused tissues. The IA perfusion resulted in more reliable cell distribution to the pastern and foot area. Potential relevance: Regional limb perfusion of MSCs might be used in cases where intralesional injection is not possible or in order to avoid iatrogenic needle damage. Further work is needed to assess the safety of IA RLP before its clinical use.     

Clinical safety of percutaneous ultrasound‐guided fine‐needle aspiration of adrenal gland lesions in 19 dogs

Objective

To evaluate the safety of fine‐needle aspiration of adrenal gland lesions in dogs and to characterise the risks in a subset of patients with cytologically or histopathologically diagnosed phaeochromocytoma.

Materials and Methods

Retrospective review of medical records of dogs that underwent percutaneous ultrasound‐guided fine‐needle aspiration of adrenal gland lesions between August 2014 and December 2016. Nineteen dogs were identified, with three undergoing bilateral adrenal gland aspiration and one dog undergoing aspiration twice, yielding 23 cytology samples in total. Data collected included signalment, concurrent medical conditions, current medications, blood pressure and heart rate before adrenal fine‐needle aspiration, imaging characteristics of the adrenal gland lesions and any clinically apparent procedure‐related complications.

Results

Phaeochromocytoma was diagnosed in nine of 19 dogs, including one dog with bilateral phaeochromocytoma. One dog developed ventricular tachycardia following aspiration of an adrenal gland lesion cytologically consistent with a phaeochromocytoma.

Clinical Significance

Percutaneous ultrasound‐guided fine‐needle aspiration of adrenal gland lesions appears to be relatively safe, even in phaeochromocytoma, but further data are required to lend more weight to this finding. Minimally invasive aspirates could be considered as part of the diagnostic algorithm in the investigation of an incidentally detected adrenal gland lesion of uncertain clinical significance.     

Autologous point‐of‐care cellular therapies variably induce equine mesenchymal stem cell migration,proliferation and cytokine expression

Reasons for performing study: Autologous cellular therapy products including adipose‐derived stromal vascular fraction (SVF), bone marrow mononuclear cells (BMMNs), cord blood mononuclear cells (CBMNs) and platelet rich plasma are options for treatment of acute orthopaedic lesions while mesenchymal stem cells (MSCs) are culture expanded. These products may contribute to healing by secreting matrix proteins or growth factors, but they may also act on endogenous MSCs to facilitate healing. Objectives: To determine the effects of cell therapy products on MSCs function in vitro. The hypothesis was that cell therapy products promote MSCs functions including proliferation, migration and mediator release. Methods: Fat, bone marrow (BM), cord blood and platelets were obtained from 6 Quarter Horses. The BM‐MSCs and their autologous cell therapy products were co‐incubated in transwells. Mesenchymal stem cells proliferation, migration, gene expression and cytokine concentrations were determined. Results: All cell therapy products increased MSCs proliferation, but SVF induced significantly more proliferation than any other product. Also SVF elicited more MSCs chemotaxis and, along with BMMNs, significantly more MSCs chemoinvasion. Cord blood mononuclear cells stimulated MSCs to produce high concentrations of interleukin‐6 (IL‐6), transforming growth factor‐β1 (TGF‐β1), and prostaglandin E₂ (PGE₂). Stromal vascular fraction and platelet lysate did not stimulate MSCs but SVF and platelet lysate themselves contained high concentrations of PGE₂ and IL‐6 (SVF) and TGF‐β1 (platelet lysate). Conclusions: Autologous cell products variably stimulate MSCs functions with 2 primary patterns apparent. Products either contained preformed mediators that may have intrinsic healing function, or products stimulated MSCs to secrete mediators. Potential relevance: The specific clinical indications for these products may differ to include administration as a sole treatment modality prior to MSCs injection for intrinsic cell and cytokine activity (i.e. SVF) or administration concurrently with MSCs to activate MSCs for treatment of chronic lesions (i.e. CBMNs).     

Surgical management of a traumatic dislocation of the sternum in an English bulldog

A nine‐year‐old English bulldog presented with an acute history of dyspnoea, tachycardia and discomfort localising to the ventral thorax following a fall down the stairs that morning. After the dog was stabilised, thoracic radiographs revealed a luxation of the third and fourth sternebrae with dorsal displacement of the caudal segment. The sternum was reduced and stabilised with a contoured 12‐hole 3 · 5‐mm dynamic compression plate applied to the ventral surface of the sternum. The dog's initial recovery was rapid, cardiorespiratory parameters returning to normal in the first 24 hours. For 2 weeks postoperatively the dog exhibited difficulty in rising from a prone position. After this time there was a full recovery. Clinical examination at 8 months postoperatively did not reveal any abnormalities. Telephone follow‐up was performed at 18 months and no complications or cardiorespiratory compromise were reported. To the authors’ knowledge, this is the first reported case of a traumatic dislocation of the sternum and its management in the dog.     

Comparative study of equine bone marrow and adipose tissue-derived mesenchymal stromal cells

Reasons for performing study: Mesenchymal stromal cells (MSCs) represent an attractive source for regenerative medicine. However, prior to their application, fundamental questions regarding molecular characterisation, growth and differentiation of MSCs must be resolved. Objectives: To compare and better understand the behaviour of equine MSCs obtained from bone marrow (BM) and adipose tissue (AT) in culture. Methods: Five horses were included in this study. Proliferation rate was measured using MTT assay and cell viability; apoptosis, necrosis and late apoptosis and necrosis were evaluated by flow cytometry. The mRNA expression levels of 7 surface marker genes were quantified using RT‐qPCR and CD90 was also analysed by flow cytometry. Differentiation was evaluated using specific staining, measurement of alkaline phosphatase activity and analysis of the mRNA expression. Results: High interindividual differences were observed in proliferation in both cell types, particularly during the final days. Statistically significant differences in viability and early apoptosis of cultured AT‐ and BM‐MSCs were found. The highest values of early apoptosis were observed during the first days of culture, while the highest percentage of necrosis and late apoptosis and lowest viability was observed in the last days. Surface marker expression pattern observed is in accordance to other studies in horse and other species. Osteogenic differentiation was evident after 7 days, with an increasing of ALP activity and mRNA expression of osteogenic markers. Adipogenic differentiation was achieved in BM‐MSCs from 2 donors with one of the 16 media tested. Chondrogenic differentiation was also observed. Conclusions: Proliferation ability is different in AT‐MSCs and BM‐MSCs. Differences in viability and early apoptosis were observed between both sources and CD34 was only found in AT‐MSCs. Differences in their osteogenic and adipogenic potential were detected by staining and quantification of specific tissue markers. Potential relevance: To provide data to better understand AT‐MSCs and BM‐MSCs behaviour in vitro.     

Multicentric mast cell tumors in a horse

Abstract: A 6‐year‐old female Rocky Mountain horse was presented for evaluation of draining tracts and distal limb subcutaneous edema on the left front and left hind limbs that had been present for 2 weeks. Direct smears of fluid collected by fine‐needle aspiration of subcutaneous fluid from both limbs were highly cellular with a predominance of eosinophils accompanied by numerous, moderately atypical, variably granulated mast cells. The cytologic diagnosis was mast cell tumor (MCT) with prominent eosinophilic infiltration with a differential diagnosis of eosinophilic granuloma. Histologic evaluation of surgical biopsies of lesions from both limbs was performed on sections stained with H&E, toluidine blue, and Luna stains. The histologic diagnosis was MCT, and staining with toluidine blue and Luna stains confirmed the presence of mast cells and eosinophils, respectively. In addition, the mast cells strongly expressed CD117. This is the first reported case of cutaneous mast cell neoplasia in a horse in which primary presenting complaints were draining tracts and distal limb subcutaneous edema involving multiple limbs. This case illustrates the utility of staining for CD117 expression in combination with traditional stains, such as toluidine blue and Luna, in differentiating MCTs from other eosinophilic lesions in horses.     

Cytological comparison of fine-needle aspirates of liver and spleen of normal dogs and of dogs with cutaneous mast cell tumours and an ultrasonographically normal appearing liver and spleen

Staging of dogs with cutaneous mast cell tumours (MCTs) is an important diagnostic step. Aspiration of the liver and the spleen is often part of routine staging. This study cytologically compared mast cell numbers in fine‐needle aspirates of liver and spleen of clinically normal unaffected dogs with those of dogs with cutaneous MCT and an ultrasonographically normal appearing liver and spleen. The unaffected dogs (n = 32) were selected from humane society dogs, and the affected dogs (n = 51) were selected from hospital cases. There were no statistically significant differences in each of the parameters evaluated for the liver aspirates. For splenic aspirates, affected dogs showed significantly more mast cells per cluster (P = 0.04) and more isolated mast cells per slide (P = 0.03) compared with unaffected dogs. However, no clinically important difference existed between the unaffected and affected dogs; thus, routine aspiration of an ultrasonographically normal appearing liver and spleen of dogs with cutaneous MCT does not appear to be a clinically useful staging tool.     

Implantation of bone marrow-derived mesenchymal stem cells demonstrates improved outcome in horses with overstrain injury of the superficial digital flexor tendon

Reasons for performing study: Mesenchymal stem (progenitor; stromal) cell (MSC) therapy has gained popularity for the treatment of equine tendon injuries but without reports of long‐term follow‐up. Objectives: To evaluate the safety and reinjury rate of racehorses after intralesional MSC injection in a large study of naturally occurring superficial digital flexor tendinopathy and to compare these data with those published for other treatments. Methods: Safety was assessed clinically, ultrasonographically, scintigraphically and histologically in a cohort of treated cases: 141 client‐owned treated racehorses followed‐up for a minimum of 2 years after return to full work. Reinjury percentages were compared to 2 published studies of other treatments with similar selection criteria and follow‐up. The number of race starts, discipline, age, number of MSCs injected and interval between injury and treatment were analysed. Results: There were no adverse effects of the treatment with no aberrant tissue on histological examination. The reinjury percentage of all racehorses with follow‐up (n = 113) undergoing MSC treatment was 27.4%, with the rate for flat (n = 8) and National Hunt (n = 105) racehorses being 50 and 25.7%, respectively. This was significantly less than published for National Hunt racehorses treated in other ways. No relationship between outcome and age, discipline, number of MSCs injected or injury to implantation interval was found. Conclusions: Whilst recognising the limitations of historical controls, this study has shown that MPC implantation is safe and appears to reduce the reinjury rate after superficial digital flexor tendinopathy, especially in National Hunt racehorses. Potential relevance: This study has provided evidence for the long‐term efficacy of MSC treatment for tendinopathy in racehorses and provides support for translation to human tendon injuries.     

The canine epiphyseal-derived mesenchymal stem cells are comparable to bone marrow derived-mesenchymal stem cells

Mesenchymal stem cells (MSCs) hold great potential in cell therapy and have attracted increasing interests in a wide range of biomedical sciences. However, the scarcity of MSCs and the prolonged isolation procedure limited the clinical application. To address these 2 issues, we developed a method to isolate MSCs from bone biopsy tissues of euthanized canine body donors. Compared to the traditional method to isolate MSCs from aspirated bone marrow (BMSCs), the isolation procedure for MSCs from harvested epiphyseal cancellous bone (EMSCs) was less time-consuming. The isolated EMSCs had similar plastic-adherence, tri-lineage differentiation and consistent surface marker profiles compared to BMSCs. We harvested BMSCs and EMSCs from 24 euthanized cases from clinics and 42 euthanized donors from a local shelter. The successful rate for EMSC isolation is significantly higher compared to BMSC isolation, while the other properties of the isolated MSCs including the clonogenicity, proliferative potentials and molecular phenotypes were not discernibly different between the MSCs established by the two methods. In conclusion, we demonstrated a new procedure to harvest MSCs by bone biopsy at the epiphyseal region. This method is less time consuming and more reliable, and the resulting MSCs are comparable to those harvested by bone marrow aspiration. The combination of the two methods can greatly improve the efficiency to harvest MSCs.     

Impact of source tissue and ex vivo expansion on the characterization of goat mesenchymal stem cells

Background: There is considerable interest in using goats as models for genetically engineering dairy animals and also for using stem cells as therapeutics for bone and cartilage repair. Mesenchymal stem cells(MSCs) have been isolated and characterized from various species, but are poorly characterized in goats.Results: Goat MSCs isolated from bone marrow(BM-MSCs) and adipose tissue(ASCs) have the ability to undergo osteogenic, adipogenic and chondrogenic differentiation. Cytochemical staining and gene expression analysis show that ASCs have a greater capacity for adipogenic differentiation compared to BM-MSCs and fibroblasts. Different methods of inducing adipogenesis also affect the extent and profile of adipogenic differentiation in MSCs. Goat fibroblasts were not capable of osteogenesis, hence distinguishing them from the MSCs. Goat MSCs and fibroblasts express CD90, CD105, CD73 but not CD45, and exhibit cytoplasmic localization of OCT4 protein. Goat MSCs can be stably transfected by Nucleofection, but, as evidenced by colony-forming efficiency(CFE), yield significantly different levels of progenitor cells that are robust enough to proliferate into colonies of integrants following G418 selection.BM-MSCs expanded over increasing passages in vitro maintained karyotypic stability up to 20 passages in culture,exhibited an increase in adipogenic differentiation and CFE, but showed altered morphology and amenability to genetic modification by selection.Conclusions: Our findings provide characterization information on goat MSCs, and show that there can be significant differences between MSCs isolated from different tissues and from within the same tissue. Fibroblasts do not exhibit trilineage differentiation potential at the same capacity as MSCs, making it a more reliable method for distinguishing MSCs from fibroblasts, compared to cell surface marker expression.     

Thirty‐two component finite element models of a horse and donkey digit

Reasons for performing study: The finite element (FE) method is the most powerful modelling technique available to explicate the biomechanics of the digit. It has already proved to be of high value in human podiatry. However, accurate models of the complex anatomy of the horse and donkey digit are currently lacking. Objectives: To develop FE models of the horse and donkey digit from computed tomography data, including all functionally relevant anatomy, and to perform simulations to replicate prestrain in the flexor tendons and quasistatic weightbearing. Methods: Computed tomography data of the front right digits were obtained under general anaesthesia. The anatomy was rationalised into 32 functional components. The FE models were generated using a forward engineering technique. Linear or nonlinear material properties were applied according to published data. Prestraining of the flexor tendons was achieved by z‐direction displacement, and loading by the application of 1 × body mass. Results: The resultant FE models comprised over 10⁶ elements. Z‐direction displacement of the digital flexor tendons to compensate for general anaesthesia relaxation gave von Mises stress levels up to 1.34 MPa for the deep and 0.56 MPa for the superficial in the horse and 0.78 MPa and 0.27 MPa in the donkey, respectively. Weightbearing resulted in capsular deformation patterns consistent with in vivo observations, and maximum stress levels of 1.46 MPa for the horse and 0.89 MPa for the donkey. Conclusion: These high resolution FE models could give new insight into the biomechanics of the equid digit and provide new data regarding stress and strain levels within the tissues of the digit that are unobtainable by other means. Potential relevance: Application of the FE modelling technique could enable investigation of the biomechanics of orthopaedic problems and may provide a mechanistic basis for enhanced preventative and remedial management and treatment.     

Isolation and characterization of bone marrow-derived equine mesenchymal stem cells

OBJECTIVE: To isolate and characterize bone marrow-derived equine mesenchymal stem cells (MSCs) for possible future therapeutic applications in horses. SAMPLE POPULATION: Equine MSCs were isolated from bone marrow aspirates obtained from the sternum of 30 donor horses. PROCEDURES: Cells were cultured in medium (alpha-minimum essential medium) with a fetal calf serum content of 20%. Equine MSC features were analyzed to determine selfrenewing and differentiation capacity. For potential therapeutic applications, the migratory potential of equine MSCs was determined. An adenoviral vector was used to determine the transduction rate of equine MSCs. RESULTS: Equine MSCs can be culture-expanded. Equine MSCs undergo cryopreservation in liquid nitrogen without altering morphologic characteristics. Furthermore, equine MSCs maintain their ability to proliferate and differentiate after thawing. Immunocytochemically, the expression of the stem cell marker CD90 can be detected on equine MSCs. The multilineage differentiation potential of equine MSCs was revealed by their ability to undergo adipogenic, osteogenic, and chondrogenic differentiation. CONCLUSIONS AND CLINICAL RELEVANCE: Our data indicate that bone marrow-derived stromal cells of horses can be characterized as MSCs. Equine MSCs have a high transduction rate and migratory potential and adapt to scaffold material in culture. As an autologous cell population, equine MSCs can be regarded as a promising cell population for tissue engineering in lesions of the musculoskeletal system in horses.