OBJECTIVE: To analyze the cellular, growth factor, and cytokine composition of equine sternal bone marrow aspirate (BMA) and laboratory-centrifuged BMA concentrate (BMAC). METHODS: This was an in vitro experimental study. Cellular composition, growth factors (IGF-I, VEGF, PDGF, TGF-β1), and cytokines (IL-6, IL-10, tumor necrosis factor-α (TNF-α), and IL-1 receptor antagonist protein [IL-1Ra]) were quantified using a standard automated hematology analyzer and ELISA methods, respectively, in donor-matched BMA, BMAC (in-house centrifugation protocol), whole blood, and platelet-rich plasma (E-PET
Pall Inc) prepared from 25 horses from 2016 through 2020. RESULTS: Leukocytes, neutrophils, monocytes, lymphocytes, and thrombocytes were increased 4.1-, 3.4-, 4.6-, 4.4-, and 2.5-fold in BMAC compared to BMA, respectively. Interleukin-1 receptor antagonist protein of BMAC was increased 21-fold compared to BMA and increased 117-fold compared to gravity filtration system-based, leukocyte-rich platelet-rich plasma. CONCLUSIONS: Laboratory centrifugation enriches the cellular and IL-1Ra concentrations of equine BMAC compared to BMA, with no significant changes in IGF-I, VEGF, PDGF, TGF-β1, IL-6, IL-10, or TNF-α concentrations. CLINICAL RELEVANCE: Equine BMA and BMAC are patient-side biologics enriched with anti-inflammatory IL-1Ra and support further evaluation of equine BMAC for musculoskeletal tissue healing.