The true mechanisms are still a bit unknown. It is one of those gray areas where there has been little research.
Use of prostaglandin F2 (PF2) will shorten the luteal phase, lysing the luteal structure (CL) to bring the mare in heat earlier
than she would on her own. But the prostaglandins have little use for the spring transitional mare, since she hasn't had an
ovulation yet. Therefore, in the spring transitional mare, there is no biological endpoint that would be affected by prostaglandin.
The other concern regarding PF2 are the possible side effects of increased heart rate, diarrhea, sweating and pelvic muscle
spasms. The side effects can be reduced by giving two injections of reduced dosage 24 hours apart.