Twinning in mares is very undesirable because of low survival rates, usually very weak foals, and numerous conformational problems. Of all twin pregnancies, 60% will birth a live single foal, 31% will abort both foals, and 9% will carry both twins to term. Of the 9% carried to term, 64.5% will birth two stillborn foals, 21% will birth one live foal and one stillborn foal and 14.5% will birth two live foals.
Origination-Dizygotic
Two separate ovulations occurring a day apart (Stop checking after 1st ovulation, mare ovulates a second time). These foals have low survival due to competition for space and nutrients.
Management
The biological reduction mechanism fails if ovulations occurred >2 days apart.
Ultrasound at 16 days and then recheck at 18-20 days.
Prior to the 20th day of pregnancy one of the embryos can be manually removed by separating the embryos into 2 horns and crushing one of them. Give the mare anti-PGF compound + progesterone for approximately 5 days after. There is no loss of time and if both are lost, it is still possible to recycle and breed.
Prior to the 35th day of pregnancy administer PGF to abort all PG’s and the mare should recycle normally.
After the 35th day of pregnancy = PROBLEMS! The mare will not cycle back for 2-3 months (endometrial cups).
