Effectiveness of a two-dose regimen of prostaglandin administration in inducing luteolysis without adverse side effects in mares.

The research investigates the method of giving horses repeated small doses of a hormone called prostaglandin F2alpha to trigger the breakdown of the corpus luteum, a structure in the ovaries, instead of a single large dose. The study claims this approach is more effective and reduces unwanted side effects.

Research Methodology

The researchers aimed to observe if the cyclic administration of the hormone prostaglandin F2alpha (PGF2alpha) would be more effective at inducing luteolysis – the process of breaking down the corpus luteum in the ovaries, which is a requisite for normal reproductive cycles in female horses, and to use smaller doses to minimize any adverse side effects.

• They used 43 mares who were in dioestrus phase (part of the mare’s cycle when the corpus luteum forms) for the primary part of the study.
• 22 of these horses were given a single 10 mg dose of PGF2alpha, while another 21 received two 0.5 mg doses of the hormone, with a gap of 24 hours between the two shots.
• The intensity of side effects was measured in 8 mares randomly given different dose levels of PGF2alpha in consecutive cycles. The doses varied between 5, 1.5, 0.5, or 0 mg.

Key Findings

The study yielded significant results that provided evidence for the effectiveness of a two-dose regimen of PGF2alpha.

• All mares that received two doses of 0.5 mg PGF2alpha showed signs of luteolysis. This was judged by a decrease in plasma progesterone levels or visible changes in reproductive behavior/tract.
• The single-dose horses (10 mg of PGF2alpha) displayed a lower proportion of successful luteolyses, with just 17 of the 22 mares showing signs of the process.
• A lone dose of 0.5 mg PGF2alpha was equivalent to a saline solution in efficacy, i.e., it had nearly no effect.
• The intensity of PGF2alpha’s side effects grew with an increase in the dose size.
• The 0.5 mg dose, despite raising plasma cortisol concentrations and stopping the decline in heart rate that would usually occur after saline, did not cause sweating or muscle spasms like higher doses did.

Conclusion

The study concluded that administering PGF2alpha in a two-dose regimen increased the hormone’s ability to stimulate luteolysis while also managing to control any adverse side effects. This regimen presents a more effective alternative to the standard single-dose treatment.