Laser ablation of the equine oviductal papilla as a novel contraceptive technique

Abstract

Reproductive control of wild horses has frustrated land management groups for decades. GnRH and Zona Pellucida vaccines have a limited duration of efficacy, intrauterine devices are unpredictably retained, and attempts to ovariectomize mares in the western United States were met with public outcry in 2018. The development of a non-surgical permanent sterilization technique has the potential to revolutionize management of wild equids on public lands. The objectives of this study were to develop a safe and effective sterilization technique for reproductively healthy mares. We hypothesized that laser ablation of the oviductal papillae would be an effective method of permanent sterilization. Seven light-breed reproductively healthy mares (5-21yrs) were enrolled in the study. On enrollment, mares were sedated for hysteroscopy, and the endometrium and oviductal papillae were examined using a 103cm flexible endoscope (Olympus GIF-160 Gastroscope, Center Valley, PA) attached to an Olympus EVIS EXERA CV-160 video processor. In five mares, a 600 μm laser fiber was advanced through the biopsy channel and a diode laser (Dornier Medilas D, Dornier MedTech America, Inc., Kenneasaw, GA) was used to deliver direct contact pulses of 3 to 5 seconds in duration to the oviductal papilla. The endoscope was then guided up the contralateral horn and the process repeated. In two control mares, the oviductalpapillae were visualized, but no laser ablation was performed. All mares received 5 mg dinoprost IM and a uterine lavage within 4 hours post-procedure. Transrectal ultrasound was performed every 2-3 days until a 35mm follicle was detected, and then mares were bred using semen from a fertile stallion. Pregnancy status was determined by transrectal ultrasound 14 days post-ovulation, luteolysis was induced, and mares were rebred on 2-4 consecutive cycles. Control mares conceived on 6 out of 9 cycles (67% pregnancy rate). Pregnancy rate was significantly lower in the treatment group (5%, 1 out of 20 cycles, p=0.003). The first mare that was laser ablated conceived on the 4th cycle, and repeat hysteroscopy determined that the left oviduct was not effectively ablated. The third mare was diagnosed with peritonitis via abdominocentesis 6 hours post hysteroscopy. The mare was treated with broad spectrum antibiotics and recovered uneventfully. Three mares were re-bred two years after the procedure and did not conceive. In conclusion, when laser ablation of the oviductal papillae was appropriately performed, scar tissue formation effectively prevented pregnancy for a minimum of four months post-procedure. Laser ablation of the oviductal papillae is a promising technique for permanent sterilization of the mare and a follow-up long-term fertility study is warranted in a larger group of mares is warranted.