What is the appropriate treatment for a horse with suspected oviduct blockage using misoprostol (prostaglandin E1 analogue)?

Misoprostol is Not Indicated for Equine Oviduct Blockage

There is no evidence supporting the use of misoprostol for treating blocked oviducts in horses, and this prostaglandin E1 analogue should not be used for this indication. The available equine reproductive literature demonstrates that mechanical interventions—specifically hysteroscopic hydrotubation with saline—are the appropriate treatment approach for suspected oviductal obstruction in mares.

Evidence-Based Treatment: Hysteroscopic Hydrotubation with Saline

The definitive treatment for suspected equine oviductal blockage is hysteroscopic selective hydrotubation using saline flush, not prostaglandin therapy 1, 2.

Clinical Efficacy Data

• In a case series of 28 mares with unexplained subfertility and presumed oviductal blockage, hysteroscopic hydrotubation with 10 mL of saline resulted in 26/28 (93%) achieving pregnancy after treatment 1.
• Prior to treatment, these mares had been bred for an average of 6.5 ± 4.5 estrous cycles without conception 1.
• After saline hydrotubation, mares conceived in an average of 1.8 ± 0.8 cycles 1.
• The procedure successfully infused saline into 50 oviducts with a 75% technical success rate for catheter placement 2.

Procedural Approach

• The technique involves inserting a catheter into the uterotubal junction under endoscopic guidance in the standing sedated mare 1, 2.
• Saline (10 mL) is flushed through the oviduct to mechanically clear any obstruction 1.
• This is a minimally invasive procedure that does not require general anesthesia 1.

Why Misoprostol is Not Appropriate

Mechanism Mismatch

While prostaglandin E2 (PGE2) does play a physiological role in equine oviductal transport by relaxing smooth muscle at the ampullary-isthmic junction, this mechanism is relevant for embryo transport timing, not for treating structural blockages 3.

• PGE2 application in research settings accelerated embryo passage through patent oviducts, allowing day-5 recovery of morulae rather than day 7-8 recovery 3.
• This demonstrates a smooth muscle relaxation effect in functional, unobstructed oviducts, not treatment of physical blockages 3.

No Clinical Evidence in Horses

• Misoprostol is a synthetic prostaglandin E1 analogue used in human medicine for various indications including cervical ripening and NSAID gastroprotection 4.
• There are no published studies evaluating misoprostol for equine oviductal pathology 1, 2, 5.
• The equine reproductive literature consistently describes mechanical flushing techniques, not pharmacological prostaglandin therapy, for oviductal obstruction 1, 2, 5.

Alternative Diagnostic and Therapeutic Options

Laparoscopic Approaches

For cases where hysteroscopic hydrotubation is unsuccessful or when more extensive evaluation is needed:

• Laparoscopic flank approach allows direct visualization and catheterization of the ampulla in standing sedated mares 5.
• This technique achieved successful catheterization in 7/11 cases, with injected fluid identified in the uterus in 5/7 cases 5.
• Transvaginal laparoscopic approaches are not appropriate for oviductal flushing in mares 5.

When to Consider Surgical Intervention

• If minimally invasive techniques fail, exploratory surgery under general anesthesia or flank laparotomy may be necessary 5.
• These remain the most invasive options and should be reserved for refractory cases 5.

Clinical Pitfalls to Avoid

• Do not extrapolate human prostaglandin protocols to equine oviductal disease—the anatomy, physiology, and evidence base are fundamentally different 1, 2.
• Do not delay mechanical intervention in favor of medical management—the evidence strongly supports early hysteroscopic hydrotubation for subfertile mares with suspected blockage 1.
• Ensure proper case selection: This treatment is indicated for mares with unexplained subfertility after multiple breeding cycles with fertile stallions, where oviductal pathology is suspected 1.