By: Melissa Sykes
For those who breed Thoroughbreds, an average live foal rate of about 60% is the norm. That’s not to say broodmare managers are content to get six foals from every ten matings during a season.
Enter the age of science.
We know more about the equine reproductive system than ever before. And we are learning new things every day. Research over the past thirty years has given us the means to regulate a mare’s cycle, extend a stallion’s sperm, predict ovulation and help the mare retain her pregnancy. Some of the weapons in the broodmare manager’s arsenal include altrenogest (ReguMate), Ovuplant and injectible progesterone.
Many farms are opting for the new drug implant Ovuplant. Approved for use in the U.S. in 1999, the drug is designed to hasten ovulation in mares. Studies conducted in the early 1990’s have shown that when a mare receives Ovuplant with a breeding follicle of at least 30 mm in diameter, ovulation will occur within 48 hours. This held true in over 88% of the mares in the study.
However, some practitioners reported that mares treated with Ovuplant were likely to experience a delayed return to estrus if they failed to become pregnant when bred during this cycle.
If the mare needs to have her estrus cycle ‘suspended’ rather than hastened, then ReguMate is the drug of choice. Recent studies have shown that when altrenogest is administered daily from the point at which a follicle is at least 35 mm in diameter, ovulation can be delayed by an average of 1.6 days. When the dosage was doubled (from .044mg/kg of body weight to .088mg/kg of body weight), ovulation was delayed by 3.2 days.
Once again, mares treated chemically to alter their ovulation, were more likely to be delayed in returning to estrus.
‘Problem’ mares abound in the Thoroughbred industry. Those, that for reasons we don’t know, have trouble maintaining their pregnancy to full term.