What if my mare did not get pregnant? Why embryo’s fail and improving odds of successful horse breeding
/Words - Jackie Bellamy-Zions
If entering the winter, your breeding prospects have come up empty, there are considerations to ponder and actions you can take for successful breeding next year. “Don’t let those mares sit all winter, with untreated conditions such as a uterine infection,” says Dr. Tracey Chenier, Theriogenologist and researcher from the Ontario Veterinary College at the University of Guelph. “Have a thorough veterinary evaluation now to help ensure her uterus is clean and she is healthy and cycling early next year, for the best chance of a positive outcome.”
Common Issues Conceiving and Potential Solutions
“The number one reason your mare didn't get pregnant in any given year may be due to uterine infection,” says Chenier. “The term we use is endometritis.” Most often caused by a bacterial infection, it is often associated with poor perineal conformation. In other words, your mare has a tilt to her vulva causing the vagina and uterus to become contaminated with bacteria every time she defecates. It is also common for these mares to wind suck, which can lead to infection and inflammation that results in a hostile environment the embryo cannot survive in. A minor surgical procedure known as a Caslick’s suture reduces the chance of contamination in most affected mares. Severely affected mares may require additional procedures to reconstruct the perineal body.
Another common form of endometritis is PBIE, or persistent breeding induced endometritis. In these cases, there is a prolonged inflammatory response to semen and contamination that occurs at breeding. Again, the mare has a hostile uterine environment in which the embryo cannot survive. To improve the chance of conception, this condition can be managed by ultrasound within 6 to 12 hours after breeding. She is checked for fluid retention and inflammation and if present, the uterus is lavaged to remove the fluid and calm the inflammation. The veterinarian may also advise administration of oxytocin to increase uterine contractions and help remove the fluid.
Another very common reason for the mare not getting pregnant is their age. “We actually consider mare’s fertility to decline as early as 12 years of age,” says Chenier, “and that surprises people that as early as 12 years, their fertility can decline significantly.” Older mares can have poorer oocyte (egg) quality. This reduces their chances of getting pregnant and can result in higher rates of mid-gestational losses.
Older mares are more susceptible to many circumstances including uterine conditions, metabolic disease, changes to the uterus, fibrosis and cysts. Fibrosis of the uterus will reduce the chances of carrying a pregnancy to term. Endometrial cysts or fluid filled sacs in the lymphatics of the uterus can block the ability of the embryo to move around and interfere with the placenta formation.
Less Common Conception Issues
“Stress, nutritional issues, and hormone deficiencies can make it difficult for an embryo to survive,” explains Chenier “but these issues are generally less common.”
The corpus luteum is the structure that forms on the ovary after the mare ovulates and its progesterone production maintains the pregnancy early on. This structure may be susceptible to effects of severe stress, illness, or inflammation in the uterus. Progesterone/altrenogest supplementation can often save these early pregnancies but the mare will have to stay on the supplements until the fetoplacental unit takes over pregnancy maintenance by 120 days. The fetoplacental unit is a crucial interface between maternal and foetal circulatory systems, providing essential nutrients and oxygen to support foetal growth and development.
Early pregnancy loss can happen from days 0–60 of gestation. To help avoid risk factors like excessive stress, ask your vet before changing or adding anything to your mare’s routine. Consult your vet before administering any vaccines or deworming products.
“Oviductal blockage is another uncommon condition,” says Chenier, “but in mares that are not conceiving and everything else is normal (no uterine infection, good stallion fertility…) it should be considered.” An effective treatment the veterinarian may suggest, involves applying the hormone prostaglandin E to the oviductal papillae, which opens the oviduct and allows that blockage to be cleared out.
Diagnostics used to investigate early embryonic loss
“A good reproductive evaluation is really important to find out the reasons why a mare either didn't get pregnant or lost a pregnancy,” says Chenier.
Veterinarians use rectal palpation, especially with ultrasound, to help detect fluid and infection. Palpation with ultrasound can detect the presence of endometrial cysts, conditions on the ovary, such as failure to ovulate and ovulatory follicles.
Cultures, gained from swabs of the uterus, are performed to detect inflammation and infection. This is helpful in cases where antibiotic use is required in order to determine what type of antibiotic to use.
Uterine biopsy is indicated in certain cases. “I recommend a biopsy in any mare that fails to get pregnant after three attempts, especially if we are not getting good answers on a swab culture and ultrasound,” says Chenier. As well as providing a prognosis, it provides a lot of information on treatment options to improve the mare’s fertility.
A biopsy can help provide better information about what's going on in the uterus and in the case of inflammation, identify the type of inflammation present.
Chronic infections are more likely to be caused by something like a dormant strep infection, and biopsy may be the only way to diagnose the fibrosis of the uterus that would be directly related to prognosis. If you found out your mare’s uterine biopsy was a Grade 3, meaning she has a lot of permanent severe changes in that uterus, her likelihood of carrying a foal to term is between zero and ten percent. This is really important information to help the breeder to decide whether they want to invest the time and money to attempt to breed a mare with a prognosis revealing these challenges.
Ultrasound is useful in identifying conditions such as endometrial cysts. Cysts can be removed by putting an endoscope in the uterus and then using either laser or electrocautery to a blade to improve a mare’s chances of pregnancy. Electrocautery involves using a heated electrode to cut or coagulate tissue during surgery. When applied to a blade, it allows for precise cutting with minimal bleeding.
“In really rare cases where all else has been ruled out, a karyotype might be considered,” says Chenier. “If it's a young maiden and everything else seems to be working, there may be a genetic reason that she's not able to get pregnant, but that would be the exception.” Karyotyping involves staining chromosomes and examining them to identify structural changes or numerical abnormalities.
Improving the odds of pregnancy
The all-important veterinary evaluation will check the mare’s general health, body condition and uterine health as well as rule out metabolic diseases like insulin resistance and Cushings.
One must ensure the broodmare’s nutritional needs are met. Calories, protein, vitamins, and minerals are all passed on to the foal while in utero. Consult your vet or an equine nutritionist to ensure your mare gets a balanced diet and to learn how her nutritional needs increase during pregnancy.
Use of light to manipulate the season is a consideration if you want to breed your mare early in the season for a January – March foal. Mares stop cycling during the winter. “I think it's helpful to expose the mare to the cold and the darkness of the fall to reset her system before you start her under lights,” say’s Chenier. She recommends lighting programs begin around December 1st with what amounts to ten-foot candles, which is equivalent to 100 lux intensity of light. In old style lighting with incandescent bulbs that was the 100 Watt bulb and the old saying was you needed to be able to read a newspaper in every corner of the stall. 16 hours of total light per day is recommended, and this includes natural light. From a practical point of view, that means if you turn your mare out at 8:00 o'clock in the morning, bring her in at four, and have the lights on in the stall until 11:00 PM, you will be providing an adequate amount of light. Chenier also describes the use of a commercially available equine light mask that is worn 24/7, like a fly mask. It is battery powered and delivers blue light to one eye on a timed basis.
“Good breeding management is always key,” emphasises Chenier. “Negative uterine swabs before breeding ensure the mare is free of infection, limit to one cover in mares prone to infection or inflammation, correcting poor perineal conformation and then practise optimal timing.”
Not breeding at the right time is much less likely in the thoroughbred industry, where mares are being bred by natural cover. If the mare is not in heat and not ready to ovulate, she is not likely to stand for the stallion.
If a mare is bred too early, the sperm will not live long enough. Mares can stay in heat a day or two after they have ovulated. If breeding happens too late (after ovulation), the oocytes will no longer be viable.
If the chosen stallion has fertility issues, the breeder may need to closely monitor their mare’s ovulation for the most optimal timing of breeding to improve odds of success. Chenier says, “If their sperm doesn't live very long inside the mare, we have to manage those cases differently and make sure we're breeding those mares really close to ovulation to get good fertility for those stallions.” Stallion fertility should always be considered a possibility when mares are not conceiving.
If breeding early in the season, one needs to make sure the mare is cycling properly and not just in spring transition. A vet check will confirm the mare is experiencing a real heat and ovulating for early breeding (Feb – April).
