By Jen Roytz

What could be that difficult about breeding? You select a stallion that suits the mare and your goals, breed your mare, then keep her fed and watered for 11 months until you’re rewarded with a healthy foal.

If only it were that simple.

There are many reasons a mare can prove difficult to get into foal, or to stay in foal. It could be as simple function of age. It could be results from a complicated delivery. Or, it could be a multitude of other reasons.

Regardless, now is the time breeders should be paying special attention to preparing their breeding stock for the upcoming season, and for those with known issues there are added safeguards and steps breeders can take she gave themselves and their horses the best chance at a successful pregnancy.

Issues that Can Impact Conception

There are many reasons a horse may have issues getting impregnated, the most basic of which are her age, not breeding her at the appropriate time during her cycle, or poor reproductive health of the mare or stallion.

A typical mare’s ovum, or egg, begins to lose viability within just five to six hours post-ovulation, and typically loses all viability within 24 hours. While a stallion’s semen typically remains viable for 48 hours, a reduced number and quality of a stallion’s semen can limit its viability to just a few hours. Age can negatively impact these timeframes for both sexes.

The mare’s body condition can also play into her chances of becoming pregnant. Most veterinarians recommend mares to rank around a 5 or a 6 on the Henneke Body Condition Score (BCS). When a mare’s weight and overall health decline, so too does their reproductive efficiency.

Outside of age and general health-related issues, endometritis is the most common reason for infertility in mares. This condition, which is an infection or inflammation of the lining of the uterus caused by foreign contaminants such as bacteria or spermatozoa, can either be acute as a result of breeding (both artificial and natural), reproductive examination or as a result of poor conformation.

“There are simple, but important steps one can take to improve the chances of conception, including a physical examination of both the mare and the stallion, a careful and thorough reproductive exam of the mare prior to the breeding season and during the estrous cycle during which breeding is to occur and to optimize the overall health of the horse,” said Kristina Lu, VMD, an equine reproductive specialist with Hagyard Equine Medical Institute.

Early vs. Late Term Pregnancy Loss

Just as there are a number of reasons a mare can be difficult to impregnate, the same can hold true for keeping her in foal. Most pregnancy losses occur in the initial weeks and months of pregnancy.

Again, age can play a role. As mares age, they may experience uterine fibrosis, which can lead to a placenta that is less-efficient in getting nutrition to the growing fetus.

Other causes for early-term pregnancy loss can be unavoidable complications, such as genetic defects or embryonic abnormalities. They can also be due to uterine infections that may have been low-grade and undetectable at the time of breeding/conception but proliferate in the subsequent weeks and months.

Late-term losses can have their own set of culprits.

“Placentitis, umbilical cord torsion, systemic illness can all cause late, and in some cases mid-term abortion in mares,” said Lu. “Diseases such as leptospirosis, equine herpesvirus 1 or 4 and equine viral arteritis are threats to a healthy gestation as well, some of which can spread quickly through a herd and may not generate obvious clinical signs other than abortion.”

Then there are also those mares that have little trouble carrying a foal to term, only to be prone to dystocias (difficulty giving birth), which can be caused by congenital abnormalities, such as contracted limbs that prevent the foal from properly fitting through the birth canal. This, in turn, can lead to oxygen deprivation in foals.

Safeguards to Protect Both Mare and Foal

While some complications are simply unavoidable, there are safeguards and protocols that can be implemented to support the gestation and delivery of a healthy foal.

“Some simple things horsemen and women can do to protect their mares and future foals are to maintain good general health of a mare, conduct thorough reproductive examinations, monitor the mare’s reproductive tract before and after breeding, ensure regular core vaccinations, consider screening for placentitis if the mare has a previous history and consider vaccinating for herpes or leptospirosis if appropriate,” said Lu. “Breeding as close to ovulation as possible can also be of benefit. On the other hand, repeated breeding during an estrous cycle (average 21 days) may increase opportunity for endometritis in some mares.”

Above all else, staying in regular communication with your veterinarian is one of the best forms of protection one can afford their mares.

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