Ask the Vet: Equine Reproduction

Question: I own a 22-year-old Warm blood mare She had a live birth in 1996. She is in good health. Can I successfully breed her?

Answer: You ask a very interesting question, which does not have a straightforward “yes” or “no” answer. There are several factors to consider when breeding the older mare. Many broodmares can successfully produce foals into their mid-twenties. You must take into consideration the overall health of the mare. Conditions such as chronic laminitis, Equine Metabolic Syndrome, Cushings disease, and even chronic lameness can negatively affect the odds that the mare will conceive and carry a foal to term. The mare’s reproductive history can also help predict her future breeding success. An aged mare that has carried a foal to term recently has a better chance of becoming pregnant than a mare that has remained barren. Older mares typically have a lower conception rate per cycle (i.e. 30-40%) versus their younger counterparts (that typically have a 60-70% per cycle conception rate). This means that you may need to breed your older mare several times in a season in order for her to conceive. Aged mares are more likely to have reproductive conformation problems than younger mares.  As the mare ages, her reproductive tract slowly succumbs to the effects of gravity, and sinks lower into her abdomen. Also, she may develop tilted vulvar conformation, or have an accumulation of urine in her vagina. All of these anatomic challenges will predispose her to a uterine infection.  Beyond the conformation of the reproductive tract, we also have to consider what is occurring on a microscopic level within the uterus. Older mares can often have scar tissue, cysts, and inflammatory cells within the lining of the uterus, which will make it more difficult or even impossible for her to produce a live foal.

The crucial first step to determine whether or not you should attempt to breed your older mare is to have a general health exam and a  “breeding soundness exam” performed by a veterinarian who specializes in equine reproduction. This will include a rectal palpation and ultrasound exam, a vaginal and cervical exam, a uterine culture and cytology, and a uterine biopsy. Other tests may be deemed necessary as well. Some clients are hesitant to spend the money on a thorough initial examination, but it will almost always save you money in the long run. A breeding soundness exam will help determine the odds that your mare can become pregnant and carry the foal to term. This will also help your veterinarian know how to best manage the mare before, during, and after insemination.

It is important to ensure that the stallion you choose is fertile, and has had his own breeding soundness exam performed recently. Live cover and artificial insemination with fresh, cooled semen are preferable. Breeding with frozen semen typically will further decrease the per-cycle conception rate, and is more inflammatory to the uterus than using fresh semen.

When managing the breeding cycle in an older mare, I believe that “an ounce of prevention is worth a pound of cure.” This means that I tend to be very proactive in trying to minimize inflammation and infection that will occur with insemination. The mare needs to have a clean uterine culture and cytology prior to breeding. I try to manage the breeding cycle so that the mare is only bred once, and as close to ovulation as possible. Often, we assist the older mare in clearing the uterine debris and inflammation by lavaging (rinsing out) her uterus 4-8 hours post breeding. Daily ultrasound examinations will help determine the optimal treatment course. If the mare does conceive, the pregnancy should be monitored carefully to ensure the health of the mother and fetus.

Perhaps the mare in question is valuable for genetic or sentimental reasons, but is a poor candidate to carry her foal to term. Advanced reproduction techniques can be used to successfully produce a foal. “Embryo transfer” is the most commonly employed technique, wherein the mare is inseminated, and the resultant embryo is removed from her uterus 6-8 days after ovulation and transferred to a recipient (“surrogate”) mare for gestation. This technique has been very successful for obtaining foals from older mares, but does require that the mare have the ability to conceive and maintain a pregnancy for about a week. If the mare’s reproductive tract is unable to accomplish this, then “oocyte transfer” can be utilized. In this procedure, an unfertilized egg is taken from the mare’s ovary, fertilized, and placed in a recipient mare for the remainder of gestation. This technique is also fairly successful, but will incur higher veterinary costs.

In conclusion, there are many factors to consider when deciding to breed an older mare. A thorough examination by a veterinarian that is proficient in equine reproduction will help determine your chances of success. Typically, breeding an aged mare will require a higher monetary investment in order to obtain a foal, but can be well worth the time and effort.