Planning and preparation prior to breeding your mare can go a long way towards getting her in foal more easily. Preparation includes light therapy for early breeding, fitness and nutrition, preventative medical care and breeding soundness exams. Spending the extra time and money on the front end can frequently help save both in the long run.
Mares are seasonally anestrous, which means they only cycle during a certain time of year. More specifically, they are “long day breeders”; their natural season for mating is in the late spring through summer, as the days are getting longer. In nature, since the equine gestation period is roughly 11 months, foals will be born in spring and early summer, when grass is the greenest and abundantly available to keep nursing mares in good flesh. However, nature’s time frame does not always fit the desired January foaling dates for certain disciplines and breed registries.
Fortunately, a mare’s cyclicity can be manipulated using lights to encourage them to cycle earlier in the year. If you are planning on getting started breeding in February or March, before the natural breeding season for horses, then those mares should be placed ‘under lights’ at least 60 days prior to breeding. A December 1st start date should have mares cycling by early February. Light therapy entails using a combination of natural and artificial lighting to increase a mare’s exposure to 16 hours of daylight total per day. This can be accomplished by housing mares in artificially lit pens or stalls starting about 4:30 in the afternoon (before sunset) and continuing until about 11 pm at night. Lighting should be bright enough to be able to read a newspaper comfortably in the darkest corner. Equally important, however, is a period of darkness at night, so make sure lights are switched off, either manually or using a timer, for eight hours a night. If you are unable to stall or place your mare in a lighted pen, special masks are commercially available that use a blue light on a timer to stimulate mares to cycle early. Studies have proven that using this type of blue light in one eye is as equally effective as stalling mares with artificial lighting to induce early cyclicity.
Fitness and proper nutrition are important factors towards getting a mare to settle easily, but also extremely important for developing a healthy foal and having an easier delivery. Regular exercise is essential for keeping mares healthy and fit for the strenuous job of baby-making and delivery. The exercise increases blood flow to all parts of the body, including the uterus, which will encourage healthy uterine function and proper fetal development. It will also strengthen hind limb and abdominal muscles, which will be extremely important during labor, as the mare gets up and down to position the fetus and for pushing the foal out. Mares in good physical condition will also bounce back more quickly after delivering and be more likely to get back in foal readily, if desired. However, fitness should not be taken to extremes, as studies have proven that mares in heavy work or training have a harder time conceiving due to stress. A balanced, forage-based diet, is also key for allowing a mare to get in foal and to develop a healthy offspring. Supplementation may be needed to help balance forages that may be lacking in the desired vitamins and minerals. Ask your veterinarian to assist you in developing a diet for your particular horse. Care should be taken to keep broodmares in good body condition. The desired body condition for broodmares is slightly heavier than for a regular horse in light exercise. Obesity in mares has been linked to smaller, less vibrant foals and precautions should be taken not to let mares get too heavy.
Several weeks prior to breeding, all annual or semi-annual veterinary medical exams should be performed. This includes vaccinations, deworming, and teeth floating. These treatments will not prevent a mare from becoming pregnant or from maintaining a pregnancy, but it is preferable to limit as many procedures and stressful events during a pregnancy as possible. Any breeding soundness exams can also be performed during this time of preparation. Older mares or mares with a history of trouble conceiving or maintaining a pregnancy will need a uterine culture and uterine biopsy performed to see if their uterus is clean and is capable of carrying and maintaining a pregnancy to term. It is recommended that all mares getting bred by live cover also get cultured prior to being bred. Caution should be taken in using stallions that do not require a culture for live breeding, as the stallions could be transmitting diseases between mares. These infections can not only decrease fertility and conception rates in mares for the season, but can also adversely affect them for the rest of their breeding careers. Samples for uterine cultures and biopsies are most accurate and easily collected when a mare is in heat. During this time, the mare’s uterus has more blood flow and a loose cervix which facilitates sample collection. Cultures and biopsies can be collected on the same cycle as breeding; however, it is sometimes more practical to wait until the next cycle to breed. This is particularly true for uterine biopsies. The added time allows test results to come back, treatments to take place, and allows the uterus to heal where the tissue sample was removed.
These recommendations are not a guarantee that your mare will get in foal on the first or second breeding, but by following these suggestions, you’ve at least done everything in your power to get your mare pregnant! The rest is up to the mare, the stallion, and Mother Nature.