A Look at Conception Challenges and Potential Solutions.

Equine Guelph Research

If your breeding prospect remains empty heading into fall, there are key factors to evaluate and steps you can take to improve the chances of success the following year.

“Don’t let those mares sit all fall and 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 to help ensure her uterus is clean and she is healthy and cycling early next year, for the best chance of a positive outcome.”

Related: Preparing for Foaling: the High-Risk Mare

Common Conception Issues 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 frequently 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.

A thorough veterinary evaluation can identify health issues and untreated conditions so they can be resolved before breeding season begins. Photo: Alamy/Yuri Arcurs

Another common form of endometritis is persistent breeding-induced endometritis (PBIE). In these cases, there is a prolonged inflammatory response to semen and contamination that occurs at breeding; 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 six to twelve hours after breeding. She is checked for fluid retention and inflammation and if present, the uterus is lavaged (washed) to remove the fluid and calm the inflammation. The veterinarian may also recommend administration of oxytocin to increase uterine contractions and help remove the fluid.

Another very common reason for the mare not becoming pregnant is her age. “We actually consider mares’ fertility to decline as early as 12 years of age,” says Chenier. It surprises people that mares’ fertility can decline significantly by age 12, she says. An older mare can have poorer oocyte (egg) quality, which reduces her chances of getting pregnant and can result in higher rates of midgestational 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 formation of the placenta.

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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 fetal circulatory systems, providing essential nutrients and oxygen to support fetal growth and development.

Consult your veterinarian or equine nutritionist to ensure your mare’s nutritional needs are met during pregnancy. Photo: Alamy/Jeremy Kruse

Early pregnancy loss can happen from day zero to day 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 (e.g., 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.

Related: Deciding Whether to Breed Your Mare

Diagnostics 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 and 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 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 learn your mare’s uterine biopsy was a Grade 3, meaning she has a lot of permanent severe changes in her uterus, her likelihood of carrying a foal to term is between zero and 10 percent. This is really important information to help the breeder decide whether 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. Karyotyping involves staining chromosomes and examining them to identify structural changes or numerical abnormalities.

“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.”

Related: Newborn Foal Care: Essential Steps for a Healthy Start

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 pars pituitary intermedia dysfunction (PPID), also known as Cushing’s disease.

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 veterinarian 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 foal to be born January to March.

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,” says Chenier. She recommends lighting programs begin around December 1st with what amounts to 10-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. Sixteen 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 a.m., bring her in at 4 p.m., and have the lights on in the stall until 12:00 a.m. (midnight), 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.

Mares do not cycle during winter. Dr. Chenier believes it’s helpful to expose the mare to the cold and darkness of fall to reset her system before starting her under lights for earlier breeding the following year. Photo: iStock/Lubo Ivanko

“Good breeding management is always key,” emphasizes Chenier.  “Negative uterine swabs before breeding ensure the mare is free of infection. Limit to one cover in mares prone to infection or inflammation, correct poor perineal conformation, and then practice optimal timing.”

Not breeding at the right time is much less likely in the Thoroughbred industry, where mares are 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.

In the Thoroughbred industry where all horses share one official birth date of January 1, foals born earlier in the year have an advantage. Starting these mares under lights at the start of December helps them begin cycling earlier in the breeding season for a foal to be born January to March of the following year. Photo: iStock/Callipso 

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 the 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.”

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Photo: Shutterstock/Pfluegler

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 true heat and ovulating for early breeding (February to April).

Equine Guelph’s Mare and Foal Healthcare tool provides many resources such as free broodmare and foal nutrition information sheets, handy checklists, and a pregnancy wheel to see how the foal develops in real time. It also offers a selection of videos featuring Dr. Chenier on predicting and monitoring foaling.

Related: Stallion Housing Affects Welfare

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Published with the kind permission of Equine Guelph.

Main photo: Shutterstock/Rita Kochmarjova