Short‐chain fatty acids (SCFAs) produced by the gut microbiota have previously been demonstrated to play a role in numerous chronic inflammatory diseases and to be key mediators in the gut‐bone signaling axis. However, the role of SCFAs in bone fracture healing and its impact on systemic inflammation during the regeneration process has not been extensively investigated yet. The aim of this study was to first determine the effects of the SCFA butyrate on key cells involved in fracture healing in vitro, namely, osteoclasts and mesenchymal stromal cells (MSCs), and second, to assess if butyrate supplementation or antibiotic therapy impacts bone healing, systemic immune status, and inflammation levels in a murine osteotomy model. Butyrate significantly reduced osteoclast formation and resorption activity in a dose‐dependent manner and displayed a trend for increased calcium deposits in MSC cultures. Numerous genes associated with osteoclast differentiation were differentially expressed in osteoclast precursor cells upon butyrate exposure. In vivo, antibiotic‐treated mice showed reduced SCFA levels in the cecum, as well as a distinct gut microbiome composition. Furthermore, circulating proinflammatory TNFα, IL‐17a, and IL‐17f levels, and bone preserving osteoprotegerin (OPG), were increased in antibiotic‐treated mice compared to controls. Antibiotic‐treated mice also displayed a trend towards delayed bone healing as revealed by reduced mineral apposition at the defect site and higher circulating levels of the bone turnover marker PINP. Butyrate supplementation resulted in a lower abundance of monocyte/macrophages in the bone marrow, as well as reduced circulating proinflammatory IL‐6 levels compared to antibiotic‐ and control‐treated mice. In conclusion, this study supports our hypothesis that SCFAs, in particular butyrate, are important contributors to successful bone healing by modulating key cells involved in fracture healing as well as systemic inflammation and immune responses.

Objective: We aimed to study the antimicrobial and pro‐healing potential of equine mesenchymal stromal cell secreted products (i.e. secretome), collected as conditioned media (mesenchymal stromal cell‐conditioned media, MSC CM), in a novel in vivo model of methicillin‐resistant Staphylococcus aureus (MRSA)‐inoculated equine thorax wounds.Study design: Prospective in vivo study.Animals: Two Thoroughbred geldings.Methods: Six full‐thickness cutaneous wounds were created bilaterally on the dorsal thorax of two horses (n = 12 wounds/horse). Wounds on the left thoraces were inoculated with MRSA on day 0. All wounds were then treated with either mupirocin ointment, MSC CM, or vehicle control (n = 4 wounds per group) once daily for 3 days. Photographs were taken to quantify wound scores and sizes, as well as samples to determine bacterial colony forming units (CFUs), at days 0, 1, 2, 3, 7, 14, 21, and 28. The wound edge was biopsied on days 0, 7, and 28, and scored histologically.Results: Inoculated wounds had more bacterial CFUs at day 1 (p < .0001) and were larger in size at day 28 (p = .0009) than noninoculated wounds. Mupirocin‐treated wounds were smaller than MSC CM and vehicle control‐treated wounds at day 28 (p = .003). Mesenchymal stromal cell‐conditioned media did not affect CFU numbers in inoculated and noninoculated wounds. Moreover, MSC CM did not affect the parameters of wound size or gross or microscopic wound scores over time.Conclusion: Mesenchymal stromal cell‐conditioned media did not exhibit antimicrobial or pro‐healing properties in the current study; however, the in vivo model of inoculated equine thorax wounds requires further optimization.Clinical significance: This pilot study contributes to a growing understanding of the equine MSC secretome as an antimicrobial and pro‐healing therapeutic for equine wounds.

Orthobiologics rich in alpha-2-macroglobulin (A2M) are being used with increasing frequency to treat equine and human osteoarthritis (OA). The glycoprotein is concentrated from whole blood, typically prepared by a commercial device, and is administered IA with the goal of ameliorating inflammation and associated pain. In recent years, numerous investigations have elucidated A2M’s mechanism of action and its effects on joint cells; however, none have used the horse as a model nor have they investigated the commercially available kit for equine orthobiologic preparation, Alpha2EQ. This narrative review presents the most pertinent work on A2M, which supports its current clinical use as an OA treatment. Alpha-2-macroglobulin has been studied in a variety of preclinical models, in vivo, and in clinical patients. As a naturally occurring and potent protease inhibitor, A2M acts to regulate key components of the OA inflammatory cascade, from cytokines and chemokines, which propagate synovitis, to disintegrins and metalloproteinases that degrade the cartilage extracellular matrix. Three main mechanisms of action contribute to A2M’s modulation of joint inflammation and concomitant OA progression across species: the bait-and-trap mechanism, direct binding interactions, and regulation of gene expression. In vivo, A2M treatment results in improved histopathology scores, gait improvement in animals, and improved patient-reported outcomes in people. Though substantial evidence exists for A2M’s anti-inflammatory effects and role in OA treatment, further studies will be required to elucidate the mechanisms of the equine orthobiologic.

Background: Persistent hemorrhage of testicular vessels is a potentially life-threatening complication of equine castration. Frequently, general anesthesia is required to retrieve and ligate the bleeding vasculature when standing wound packing and retrieval of the spermatic cord are unsuccessful. We propose standing laparoscopic ligation of the testicular arteries via the paralumbar fossa as a rapid, effective means of halting hemorrhage while avoiding castration site trauma as well as the cardiovascular and recovery risks of general anesthesia. Methods: Two geldings, 6 and 9 months old, presented for emergency treatment of severe post-castration hemorrhage of 10 and 24 h durations, respectively. Both geldings underwent standing laparoscopy under light sedation and the testicular vessels were ligated using a bipolar vessel-sealing device. Results: Testicular vessel sealing was successfully performed in both geldings by standing laparoscopy and resulted in immediate cessation of hemorrhage. In one case, a left paralumbar fossa approach allowed coagulation of both the left and right spermatic vessels. The procedure time was 25 and 35 min. No complications occurred, and both geldings recovered uneventfully. Conclusions: Standing, laparoscopic ligation of the testicular arteries is a feasible emergency treatment in young geldings and can be applied in cases of uncontrolled post-castration hemorrhage.