Older mares can be bred successfully, but they may require some extra management and precautions during breeding and post-foaling than younger mares. It helps that your mare is in great shape and that she previously has been bred successfully.
Before you decide to breed her, you should get an equine veterinarian to evaluate her for breeding soundness. He/She will probably do palpation/ultrasound to evaluate the condition of her reproductive tract and will probably want to do a cytology (to detect cells indicative of a reproductive tract infection) and an uterine biopsy (to assess the uterine capability to maintain a pregnancy). Discuss insemination options with your veterinarian (natural cover, artificial insemination, frozen semen). Many older mares have difficulty clearing up the natural inflammatory response of the uterus to semen, so a correctly timed single insemination using artificial insemination techniques often works best. Flushing the uterus post breeding and/or administering oxytocin (hormone that causes uterine contractions) post breeding may also help clear the inflammatory response.
After the mare is bred, she also may need hormone therapy (progesterone) during her first trimester to help her maintain the pregnancy.
Other problems that are more common in older mares are ruptures of the abdominal wall, prepubic tendon, uterine ligaments, and uterine artery. These problems usually occur in late pregnancy, so efforts should be made to keep late-term mares quiet, yet as fit as possible (turn out with other late-term mares is usually recommended).
Also many older mares require large quantities of concentrates post-foaling to maintain their body condition. Making sure that the mare has access to good quality grass or hay and feeding a concentrate ration with a high fat content will help mares maintain body condition after foaling.
As mares age, their reproductive capability decreases. Older mares (20 plus years) tend to have some scarring in their uterus and lower or eratic hormone levels. Therefore, they are more challenging to get bred and to maintain pregnancy. However, mares are individuals, and some mares are reproductively active at an old age. Have a veterinarian check your mare's body condition, reproductive tract for abnormalities, and hormone levels. If all fall within the normal range, you will have a good chance of producing a foal.
