Influence of Follicle Number and Reproductive Cyclicity on Mesenchymal Stromal Cell Yield Isolated From Equine Ovarian Follicular Aspirates.

Follicular aspirates have emerged as an alternative source of mesenchymal stromal cells (MSC) in mares; however, factors influencing successful MSC isolation remain unclear. This study evaluated whether reproductive cyclicity and follicle count affect MSC recovery from ovum pick-up (OPU)-derived follicular aspirates. Twenty-eight OPU procedures were performed on 13 mares, and cells were cultured until passage 3. Successful MSC cultures were obtained in 15/28 procedures (53.6%), while 13 procedures (46.4%) yielded non-MSC populations. Neither reproductive status (cycling vs. anestrous) nor follicle count influenced MSC culture success. Interestingly, unsuccessful cultures showed significantly higher cell counts at passage 0 compared to successful cultures (p < 0.001). Receiver operating characteristic curve analysis revealed that passage 0 cell count was an excellent predictor of culture failure (AUC = 0.923; p < 0.001), with a threshold of ≥ 700,000 cells. These findings demonstrate that OPU-derived follicular aspirates represent a reliable MSC source and that high initial cell count predicts culture failure, providing a practical early screening tool for MSC production.