Effectiveness of a two-dose regimen of prostaglandin administration in inducing luteolysis without adverse side effects in mares.
Authors: Irvine C H G, McKeough V L, Turner J E, Alexander S L, Taylor T B
Journal: Equine veterinary journal
Summary
# Editorial Summary Inducing controlled luteolysis in mares is essential for breeding programmes, yet traditional single-dose prostaglandin F2alpha (PGF2α) protocols often require high doses that trigger unwanted systemic effects including sweating, muscle tremors and cardiovascular changes. Irvine and colleagues investigated whether mimicking the mare's natural pulsatile prostaglandin secretion pattern—administering two 0.5 mg doses 24 hours apart—could achieve superior luteolytic efficacy compared to the standard 10 mg single injection across 43 dioestrous mares. The two-dose regimen successfully induced complete corpus luteum lysis in all treated mares (confirmed by both progesterone decline and oestrous behaviour), significantly outperforming the single 10 mg dose which achieved luteolysis in only 17 of 22 animals (77%), whilst a single 0.5 mg dose proved no more effective than saline control. Critically, the divided low-dose protocol substantially reduced adverse side effects—the 0.5 mg dose produced minimal sweating or muscle spasms and avoided the tachycardia observed with larger doses, though it did elevate cortisol transiently. For equine practitioners managing breeding schedules, this protocol offers a practical alternative that improves both reliability and welfare by achieving 100% luteolytic success with substantially lower systemic burden, making it particularly valuable for mares with known sensitivity to prostaglandin-induced side effects.
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Practical Takeaways
- •Use a two-dose regimen of 0.5 mg PGF2α given 24 hours apart for more reliable corpus luteum regression in mares scheduled for breeding, with superior efficacy to single-dose protocols
- •The reduced dose per administration (0.5 mg vs 10 mg) significantly decreases adverse systemic effects including sweating, muscle spasms, and cardiovascular changes, improving animal welfare during estrous synchronization
- •Single low-dose PGF2α injections (0.5 mg) should not be relied upon as they offer no advantage over saline; always use the two-dose protocol for clinical effectiveness
Key Findings
- •Two doses of 0.5 mg PGF2α administered 24 hours apart induced luteolysis in 100% of mares (21/21), compared to 77% (17/22) with a single 10 mg dose (P = 0.0485)
- •A single 0.5 mg dose of PGF2α was no more effective than saline placebo in inducing luteolysis
- •The two-dose 0.5 mg regimen caused fewer adverse side effects (sweating, muscle spasms) than higher single doses while maintaining efficacy
- •PGF2α side effects including elevated plasma cortisol and increased heart rate increased with dose, demonstrating dose-dependent toxicity