University of wisconsin-madison

Synchronization of Ovulation

Unless one has lots of recipient mares to choose from (30 or more), having a mare that ovulates at the same time as the donor will require synchronization by hormonal treatment. It is more difficult to synchronize mares than cattle because of the cycle variation in the mares and the long period of estrus. Recipient mares should ovulate from 1 day before to 2 days after ovulation of the donor mare. If a large herd of recipients is available, then a recipient with the appropriate ovulation day can be selected. If a large number of recipients are not available then hormonal treatments can be used to synchronize the donor and recipient. The potential treatments are:

  • PGF2a given 2X, 14 days apart
  • Regumate for 14 days
  • Progesterone (150 mg) + Estradiol-17B (10 mg) given IM

*for all treatments, give hCG when a 35 mm follicle is present to insure ovulation in 24-48 hr

If the recipient ovulates more than 3 days after the donor, the recipient can be given 300 mg/day progesterone IM for 5 days starting on the day of ovulation. If the recipient ovulates more than 5 days after the donor, do not use the recipient.

Ovarectomized recipient

It is possible to use a recipient that has had her ovaries removed (ovarectomized). Progesterone is given to such a recipient (300 mg) beginning 2 days after the donor ovulates. After the embryo is transfered, progesterone is continued until day 100-150 of gestation. Pregnancy detection by ultrasound at day 15 is suggested and if the mare is not pregnant, then progesterone supplementation can be discontinued. The progesterone is given as IM injection but after day 335 - 40 of gestation can be switched to Regumate which can be given orally. While management of the mare is easy using this method, the progesterone costs up to $10/day of treatment.

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