Characterization of Cytokines in Donkey Follicular Fluid and Seminal Plasma: A Pilot Study

Post-breeding endometrial inflammation is a well-known physiological response in jennies, especially after artificial insemination with frozen-thawed sperm. Bioactive molecules present in reproductive fluids, including cytokines, may contribute to regulating these immune processes. The aim of this study was to characterize the cytokine profile of preovulatory follicular fluid (FF) and seminal plasma (SP) in donkeys and to explore their potential relevance for reproductive physiology. To this end, 10 FF samples were collected from five fertile Catalan jennies, and 10 samples were isolated from 10 different Catalan jackasses' ejaculates. Cytokine concentrations were measured using a Luminex MagPix system with an equine-specific Milliplex MAP panel. Three cytokines were detected in the FF, with IP-10 being the most abundant, followed by IL-10 and eotaxin. The SP, in contrast, showed a broader cytokine profile, with 10 detectable mediators. Fractalkine was the most abundant cytokine in this biofluid, followed by FGF-2 and G-CSF. GRO and IL-1β were present at intermediate concentrations, and IL-8, IL-13 and IL-12 were observed at low concentrations. From the 10 cytokines detected, IP-10 and eotaxin were found at the lowest concentrations. These results provide the first description of cytokines in donkey FF and SP. The presence of chemotactic and immunomodulatory cytokines in these reproductive fluids suggests they may contribute to the regulation of follicular processes and the post-breeding inflammatory response in jennies.