When an equine owner makes the decision to breed their mare, they began to make plans for the future; the future of the foal to be born. Once the mare is deemed in foal by the veterinarian the equine breeder turns to thoughts of raising a healthy foal and what they want the foal to become. At this point producing equine twins may be the furthest thought from a breeder’s mind, but in reality, twinning happens to be one of the main causes of abortion in mares.
Most equine twins are aborted either naturally or by a veterinary procedure before being carried to full term. Those that do survive the entire pregnancy will have difficulty surviving the birth as will the mare. As exciting as a mare with twins by her side can be, twinning is a dangerous recipe for disaster in the world of breeding horses.
“Those that survive the actual birth are typically small and weak, and may not endure to become productive athletes,” says Dr. Kenton. H. Arnold of Equine Veterinary Services in Terrell, Texas. “The probability of a difficult birth, retained placenta and other complications greatly increases the risk that the mare herself may not even survive the delivery process if she is carrying twins. If the broodmare does survive a birthing of twins, getting the mare back in foal is oftentimes difficult.”
According to Dr. Arnold, all bred mares should be sonogrammed for twins, even if double ovulation is not suspected. “The best time to check for twins is 13 to 15 days after ovulation. At this time, the embryo will appear on an ultrasound exam as a small black sphere. The embryo will still be mobile or floating about the uterus lumen at this point. If two embryos are found, then one can be manipulated away from the other and manually crushed. The crushing technique has a high success rate and the other embryo usually survives the process,” says Dr. Arnold.
The embryos will become fixed and are not moveable after day 16. “Often when the embryos are adjacent, one will spontaneously reduce from the influence of the other. Because of this natural reduction phenomenon, we usually leave the two adjacent embryos and recheck on day 29 after ovulation. If one is present, no treatment is necessary, but if both are present, they both should be aborted with a prostaglandin shot given to the mare,” says Dr. Arnold. “The mare will come back into heat shortly and can be bred on that cycle.”
If twins are carried past 36 days the endometrial cups will have been formed, and the pregnancy will be stabilized. At this point, if the mare aborts, she most likely will not come back in to heat during the current breeding season. “Any mare found to have twins that are more than 40 days old should still be aborted to protect the mare and have her in breedable shape for the beginning of the next season,” says Dr. Arnold.
It is best to have broodmares checked by ultrasound between day 13 and day 15 of the breeding cycle, and then again before day 30 to avoid a twinning disaster. The cost in time and money for the examinations will be a good investment in the health of both the mare and unborn foal. The payoff for mare owners should be one healthy foal!
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