Early foal losses in mares - DVM
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Early foal losses in mares
Stress, nutrition, season, climate, sire, rectal palpation effects, ultrasound, iatrogenic factors all extrinsic factors


In veterinary practice with Thoroughbred horses, this is especially essential with the understanding of the economics of breeding and the importance to maximize live foal births.

FlushingTo help remove any contaminated material, it is also simultaneously helpful to flush the mare.

Even semen may be irritating to the lining of the uterus, which can be significant in the sub-population of mares that have delayed uterine clearance.

Uterine lavages are used this way. After they are bred, mares likely to experience problems related to uterine clearance are often scanned to see if they retain fluids. Post-breeding lavages of sterile fluids are used to reduce the amount of contamination a mare might have post-breeding.

Caslick's procedureIn addition to post-breeding infusions, the Caslick's procedure is also used to ensure the mare's reproductive tract is kept clean.

It is done to help prevent the mare's reproductive tract from aspirating air into the vagina, allowing for ascending bacteria to enter through the cervix and reach the caudal reproductive tract. The vulvar lips are sutured together at the level of the pelvic brim to eliminate this problem, as well as episodes of urine pooling.

Veterinarians sometimes treat mares with supplemental progesterone for various reasons.

Progesterone up until a mare is 110 to 120 days pregnant is paramount to maintaining her pregnancy. Luteal insufficiency or lysis of the CL interrupts natural progesterone supplementation. If a mare's foal is ill and she is confined in the stall with it, this stress can lead to falling progesterone levels.

Mares might experience an episode of colic, due to excessive ingestion of spring grass. A colicky mare may release endotoxin causing release of prostaglandin and subsequent CL lysis and progesterone decline, therefore stall confinement stress and colic might necessitate veterinary intervention of progesterone supplementation.

When mares are ultrasounded for pregnancy at about 15 days they are often checked for uterine tone.

If their tone is noted as really poor, a progesterone assay is done to check progesterone levels. If her progesterone is less than 4ng/ml, then it may be decided to give her supplemental progesterone.

"It is one of the things we see and identify in some mares," Brown explains.

A mare may not be pregnant at day 15 to 16 post-ovulation due to whatever reason. Commonly in central Kentucky, most veterinarians are ultrasounding mares 14 to 15 days post breeding, as opposed to doing it at 17 to 18 days.

At this earlier time a lot more twins, or even triplets are discovered. Done as a precaution, these excess embryos in the mare's uterus are manipulated to reduce the number to a single embryo, so that the mare carries only one fetus to term. If not, she might naturally lose them all to early embryonic death or late term abortion.

The mare seems to have her own 'embryo reduction mechanism,' eliminating a twin on her own, which may be a part of her recognition of pregnancy phenomena. Even so, the probability is better improved with veterinary manipulation. During the process of 'squeezing' out the excess embryos, inflammation may be caused inadvertently, which may result in the loss of the pregnancy. Therefore, once again, as a precaution, supplemental progesterone is provided to sustain the single pregnancy's success.

"We do all these veterinary procedures in an attempt to create the best uterine environment," says Brown. "With such procedures the mare is less likely to suffer early embryonic death. All the precautionary things that you do can only improve the mare's conception rate and fertility. In the background of all these losses, mares, compared to other animals, even women, are a pretty strongly scrutinized group."

SummaryEarly embryonic loss occurs in the population of mares each breeding season.

Whether due to intrinsic or extrinsic factors, some of these factors have a role to play in particular mares. For each mare embryonic loss may be multi-factorial.

"I think it's one of those things that's just accepted," Sheerin says. "There's a certain percentage of pregnancy loss and it is just going to happen. We try to do the best job that we can do, so that farm managers are breeding a reproductively sound mare with a relatively fertile stallion and end up with a positive outcome. Unfortunately, there are just some mares that are going to lose their pregnancies. We can't always figure out why. People concede that there is a certain percentage of mares that will come up empty and we will try to get them bred again this year or next."

Mare management, which farm managers have in their control, is extremely intense, especially in Thoroughbred breeding. Their ability to properly care for the mare during foaling and breeding, maintain excellent nutrition and health and eliminate stresses in her environment, are each important in reproductive success.

With careful management and veterinary monitoring using ultrasound, hopefully a healthy full-term foal will stand and suckle her dam. Veterinary interventions and good management practices will help to ensure that outcome.

Dr. Kane is a freelance writer for equine topics and senior nutritionist with Stuart Products, Inc., Bedford, Texas. He holds a Ph.D in equine physiology and nutrition from the University of Kentucky.


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