Summary222 barren mares of different breeds underwent operative hysteroscopy for the treatment of uterine cysts during an eleven year period. Hysteroscopy was performed under sedation. Mares were in di-or anoestrus. Uterine distension was standardized with an intrauterine pressure between 20-30 mm Hg. Thermical preparation was achieved with high-frequency electrosurgery using micro instruments through the working channel of the endoscope. All visible cysts were resected with an electrosurgical loop. The loop was tightened around the base of the cyst and the cyst pulled towards the uterine lumen before resection. Small cysts which could not be fixed with the loop were coagulated. With the standard procedures, operative hysteroscopy could be completed with resection of all visible cysts in all the mares without complications. Therefore, the technique described here proved to be safe and efficient in a large number of treated mares. Compared to other preparation techniques, risk of recurrence is minimized, trauma of the tissue is only superficial and the wound healing is uncomplicated. The results of patho-histological examination of endometrial biopsies and of clinical follow-up with high rates of treated mares conceiving and foaling are presented in the second part of this study by Köllmann et al. (2008).

SummaryUterine cysts are a common finding during routine transrectal ultrasound examination, often associated with reduced fertility. The aim of this study was to analyse long term fertility of mares after hysteroscopic cyst removal regarding to patho-histological findings. In this study 251 transendoscopic intrauterine surgeries have been performed in 222 barren mares with uterine cysts during the last 11 years. Postoperative endometrial biopsy samples were taken in 83.6% (210/251) of the cases and were analysed and classified according to Kenney and Doig (1986). Pregnancy outcome of 74% of treated mares is known. A postoperative pregnancy rate of 79% (146/184) could be achieved. Especially in mares having biopsy category II b and III good pregnancy rates (70%/69%) could be reached. Cyst recurrence rate in years following treatment was 33.8% (60/177). We conclude that long term fertility can be improved after endouterine surgery, especially in mares having biopsy category II b and III.