Breeding and Reproduction Tips

People are always looking for tips on how to do things better--particularly horse breeders looking for ways to get healthier foals. At the recent Healthy Horses Workshop, an owner education session held Dec. 2, 2006, in San Antonio, Texas, in conjunction with the 52nd annual American Association of Equine Practitioners Convention, Benjamin Espy, DVM, Dipl. ACT, a practitioner from San Antonio, offered insight on many areas of equine reproduction to help breeders do just that.

Embryo Survival and Monitoring

"Horse embryos are not more fragile than other species', but they are less reproductively efficient for other reasons," he began. "Embryos have a 10-15% chance of being resorbed before 30 days gestation because of mare stress (leading to prostaglandin hormone release that upsets the hormone balance in the uterus and can terminate the pregnancy), fever, uterine infection, hormone abnormalities, and twinning."

Espy discussed ways of teasing and monitoring the mare to confirm pregnancy, and he reported timeframes for determining the sex of the fetus via ultrasound. "Starting on Day 58, the genital tubercle (seen as a tiny medial elevation on the embryo just ahead of the urogenital orifice) will migrate back toward the tail if the fetus is female or forward toward the prepuce if the fetus is male," he said. "We can evaluate this between Days 60-70 or Days 110-140. It's difficult or almost impossible to see between Days 80-90, and after Day 140.

He also described the timeline of several important events during gestation, and he explained the newly recognized importance of endometrial cups. These small structures form in the uterus around Day 35; they secrete the hormone pregnant mare serum gonadotropin (PMSG or equine chorionic gonadotropin, ECG), which helps maintain pregnancy.

"Once she is under the influence of these cups, she won't re-cycle for the rest of the year if she aborts," Espy summarized.


"Ninety-five percent of twins will be aborted. If they are born, 90% will die," said Espy. "They can be only about 40 pounds each--we use dog blankets on them. There's limited room in the uterus, so the mare can't really maintain both. She grows them to maximum capacity, then expels the fetuses."

This is the reason why most practitioners choose to crush or "reduce" the smaller one at about 14 days of age so the other can live.

"Up to 25-35% of Thoroughbreds can have twins," said Espy. "In my primarily Thoroughbred Lexington (Kentucky) practice, I pinched about one to three per day. Here (in San Antonio, where he works mostly with Quarter Horses), I have done about four total. Quarter Horses seem to be more efficient at rejecting one twin."

Following crushing of one twin, the other is monitored carefully for a few days, as Espy says the trauma of the reduction procedure can sometimes lead to the demise of the remaining embryo.

Tips on Managing Mares

Fitness "Foaling is an athletic activity!" stated Espy. "Mares should be fit to foal uneventfully. They shouldn't be under- or overweight. I like to ask owners to keep mares in shape and exercise them as much as possible. Pasture exercise is sufficient. Typically the horse will tell you when it's time to lay off of her if you're riding, maybe around five or six months when her stamina starts falling off. If they are jumpers or hunter/jumpers, they start knocking down fences, their coordination is not as good, and they're just feeling pregnant.

"Also, athletic horses have the best perineal (external genital) conformation," he went on. "Underweight or old horses (with poor muscle tone and a recessed anus) defecate onto the vagina, and the resulting contamination makes it difficult to get them in foal. Plus underweight mares put more energy into survival, leaving less for reproductive efficiency."

Nutrition "Pregnant mares should be fed exactly the same as nonpregnant mares for the most part," Espy recommended. "In the last two months only, feed 1.4 times her regular ration. Once you find out a mare is pregnant, don't pour the feed to her." He also noted that supplementation is not necessary in mares getting a balanced ration.

He said pregnant mares can drink up to 15-30 gallons of water per day depending on their size and the outside temperature. He warned owners against allowing mares to get dehydrated, as they can drink too much when water is available again, resulting in colic, stress, and the risk of abortion.

Deworming "Almost all deworming medications are safe for use in pregnant mares," Espy said. "When I was in school, they told us it took $3-5 million to change a label on a medication. The reason things don't say 'safe for pregnant mares' is because you have to get a different label. To say something is safe for adult horses, pregnant mares, breeding stallions, etc., requires all different labels. People don't bother with that, so most veterinarians just use them extralabel. I have never had a mare abort after using commercially available deworming products."

Ivermectin is a key ingredient given before or at foaling, as this will kill ascarids that can pass in the milk from mare to foal. He also recommended removing manure from stalls and pastures and using a disc harrow on fields to decrease parasite populations.

Neonatal isoerythrolysis (NI) screening Within two weeks of her expected foaling date, the mare should be tested to see if she has hypersensitized herself to the foal's blood type, said Espy. If she has, she cannot be allowed to suckle the foal for 24-36 hours or he will suffer from NI--the antibodies from the mare will attack the foal's red blood cells, making him very sick or killing him.

Vaccinations Thirty days before foaling, vaccinate the mare against diseases you want the foal to be protected against.

Caslick's procedures Thirty days before expected foaling, Caslick's procedures (which seal the upper vulva shut to reduce chances of uterine contamination) should be opened to avoid tearing during foaling, said Espy.

When Will She Foal?

The mare's udder fills two to four weeks ahead of foaling, said Espy. Her bag should be full with the teats pointed straight down and maybe a little forward; they should distend four to six days before foaling. You should see waxing of the teats one to four days before foaling (usually 24-48 hours ahead). You might also see subtle signs such as conformation changes as the mare's pelvic ligaments relax in preparation for foaling.

Calcium levels in mare's milk can also help tell when she'll foal. "Test kits are really nothing more than water hardness kits you can get from Lowe's and Home Depot for about one-third the cost," he said. The calcium increases in the milk 24-48 hours before foaling--when you see this, parturition is imminent, he said.

Vaginal discharge or dripping milk can indicate impending abortion or foaling, he noted.

"Some people say the fetus determines the day of delivery and the mare determines the hour," Espy commented. "Horses are prey animals. The only way a mare can survive if she is being chased is to be able to delay labor. The same thing is true in a barn--the mare getting spooked or hassled won't foal until you turn off the light and leave her alone."

As far as inducing foaling, he said mares are generally only induced for human convenience. Ask your veterinarian about this, he recommended, commenting that most veterinarians are becoming more reluctant to induce foaling unless the mare's life is in danger.

Where Should She Foal?

Outdoors "This is quite acceptable; I see a lot of problems with mares getting cast in 12x12 stalls and stepping on babies," Espy said. "An open grassy field is cleaner, and the mare can't hurt herself on any walls."

Indoors This is acceptable if a large foaling stall or other area 14x14 or larger is available. Disinfect floor mats between foalings and use straw for bedding; shavings can get packed in the foal's eyes and cause ulcers, he noted.

Foaling Stages

Stage 1: The mare is anxious, kicks at her belly, might have nesting behavior (piling up bedding to lay on), and might be mistaken for a colicky mare because she gets up and down, urinates excessively, and sweats. Many people who foal mares for a living call a sweaty mare in Stage 1 labor "heating up." Wrap her tail and clean her udder and vulva thoroughly with mild soap. This stage usually lasts an hour, or until her water breaks.

How do you tell the difference between Stage 1 labor and colic? The only way to diagnose a mare that might have abdominal pain is to ask your veterinarian. Often when the veterinarian is on the way to check the mare, she progresses to Stage 2 labor.

Stage 2: Expect to see continuous progress of the foal out of the mare; this stage usually lasts 15-25 minutes, he said. Once the foal is out, don't cut the cord--allow the foal to break it on his own. For disinfection, don't use strong iodine since there might be a higher incidence of umbilical abscesses with this treatment; Espy recommended the disinfectant chlorhexidine.

Stage 3: This is when the placenta passes. If the placenta doesn't pass after about three hours, call the veterinarian. Retained placenta can cause uterine infection and laminitis.

What To Do If...

Mares abort Save aborted fetuses and placentas in a refrigerator or cooler until your veterinarian or diagnostic lab can examine them, recommended Espy. The placenta is just as important as the fetus.

You see a red bag (placenta delivering before the foal) Cut the placenta and deliver the foal immediately! You don't have time to call the vet, he warned. The foal and the placenta are detached from the mare and the foal is being deprived of oxygen.

Call the Vet, Quick!

Espy recommends calling your veterinarian if:

  • You fail to see progress during foaling.
  • You see the soles of the foal's feet facing up. This is always a caudal, or tail-first, presentation of the foal.
  • You see front feet and knees out, but no head. This means the foal's head is trapped back, and it is a big problem.
  • You see a red bag delivery, as mentioned above.

Foal Care Tips

For some foals, Espy said you might have to stimulate breathing by sticking fingers in his nose and/or rubbing his coat. He also said normal foals follow the 1-2-3 rule: Standing in one hour, showing ability to nurse in two hours, and nursing in three hours. They should be given an enema to aid passage of the meconium, or first feces.

"Foals are born with no immune system, so they need colostrum (the mare's first milk, which contains antibodies that will protect the foal in early life)," he said. "It used to be thought that the majority of antibodies are absorbed in 12 hours. We now know the majority (85%) is absorbed in six to eight hours." He recommended milking the mare to get colostrum if the foal doesn't nurse well; you should get 16-32 ounces and give it to the foal via nasogastric tube if he doesn't nurse on his own. He also recommended pulling blood to check antibody levels six to eight hours after foaling.



Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse's AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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