Breeding the Older Mare

By the time the June issue reaches readers, the regular breeding season is winding down for many horse owners. Some mares are already confirmed in foal, some breeding decisions have been pushed aside for another year and some owners are already thinking ahead to next season. For those with an older mare they hope to breed, that early planning can make a real difference.

Older mares can still produce foals, but they may need more help than younger mares. Age affects the reproductive system, and those changes can make it harder for a mare to become pregnant, stay pregnant or carry a healthy foal to term. That does not mean every older mare is a poor candidate for breeding. It does mean owners should go into the process with realistic expectations and a good veterinarian involved from the beginning.

A mare’s reproductive age does not always match her number of birthdays. Some mares in their mid-to-late teens settle easily and carry foals without much trouble. Others begin having problems earlier. Past reproductive history matters. A mare that has had regular foals may be different from an older maiden mare that spent most of her life showing, racing, working or sitting open. Health, body condition, uterine health and conformation all play a role.

One of the main challenges with older mares is egg quality. As mares age, their eggs age, too. Older eggs are more likely to have abnormalities that prevent fertilization, stop early embryo development or lead to early pregnancy loss. Even when breeding is timed well and the stallion has good fertility, the mare may not settle because the egg itself is no longer as viable as it once was.

The uterus also changes with age. The lining of the uterus, called the endometrium, can become less healthy and less able to support pregnancy. Over time, some mares develop fibrosis or scarring within the uterus. This can interfere with the placenta’s ability to develop and support a growing fetus. A mare may get pregnant early, but then lose the pregnancy because the uterus cannot maintain it.

Older maiden mares can face an additional problem. When a mare cycles, it is normal for some fluid to be present in the uterus. A healthy reproductive tract clears that fluid through uterine contractions and cervical relaxation. In some older mares, especially those that have never had a foal, the cervix may not relax well enough. Fluid can build up and remain in the uterus after breeding. That fluid can damage sperm, interfere with an embryo and increase the risk of infection or inflammation.

Post-breeding inflammation is another concern. All mares experience some uterine inflammation after breeding, but most clear it within a reasonable amount of time. Older mares may not clear it well. This can leave the uterus in a poor environment for pregnancy. A veterinarian may recommend uterine lavage, medication or other treatment after breeding to help the mare clear fluid and inflammation.

External conformation can also affect fertility. As some mares age, especially taller, thinner mares or mares that have had multiple foals, the reproductive tract may tilt in a way that allows manure or air to contaminate the vulva and vagina. Poor vulvar conformation can increase the risk of uterine infection. In some cases, a veterinarian may recommend a Caslick’s procedure to help protect the reproductive tract.

Because so many factors can be involved, an older mare should have a breeding soundness exam before the next season begins. This may include a physical exam, reproductive ultrasound, uterine culture, cytology and possibly a uterine biopsy. These tools help determine whether the mare has infection, inflammation, fluid retention, poor uterine health or other issues that need to be addressed before breeding.

Timing is also important. With an older mare, it is usually better to start early in the season rather than waiting until late. More cycles give the veterinarian more chances to manage the mare properly. Early planning also allows time to treat infection, improve body condition, schedule semen shipments, evaluate the stallion’s fertility and consider whether cooled semen, frozen semen, live cover or another option makes the most sense.

Owners should also look closely at the mare’s overall health. A mare that is too thin, too heavy, metabolically unstable, lame or dealing with chronic illness may struggle to conceive or carry a foal. Good nutrition, dental care, hoof care and vaccination planning all matter. Breeding may be a reproductive decision, but pregnancy affects the whole horse.

For some mares, advanced reproductive options may be worth discussing. Embryo transfer allows a valuable mare to produce a foal without carrying it herself. This may be helpful for older mares that can produce an embryo but should not carry a pregnancy, or for mares that are still competing. Other assisted reproductive techniques may also be available through specialized equine reproduction centers.

The hard truth is that breeding an older mare can take more time, money and patience. Not every mare will get in foal, even with good care. Some mares should not be bred if the risks are too high. Still, many older mares can produce healthy foals when problems are identified early and managed correctly.

For owners hoping to raise one more foal from a favorite mare, the best plan is to start the conversation before breeding season arrives. Talk with a veterinarian, evaluate the mare honestly and make decisions based on her health, history and reproductive exam. Hope is part of breeding horses, but planning gives that hope a much better chance.