Prepare your Mare for Breeding Season

Use these five tips to prepare your mare for breeding season and ensure she stays healthy.

By Thiago Boechat, With Kaycie Timm; Photos by Kaycie Timm

The key to a successful breeding season starts with a healthy mare. Whether you have one broodmare or a full-scale operation, these proven tips will help you prepare before it’s time to breed.

Group of mares walking along fence in pasture
Keeping your mares under lights allows you to regulate their cycles by extending the amount of time they perceive as “daylight.” You’ll want to bring your herd in before dark and keep them in a well-lit area until around 10 p.m., then again starting from about 5 a.m. until full daylight.

Tip 1: Culture your mare to check for infection. Ensuring that your mare starts breeding season on a healthy note begins long before spring. In fact, the best time to start preparing is at the end of the preceding season. 

Before you shut down your mare, culture her to check for infection. If your veterinarian discovers anything that causes concern, treat the infection, then, at the start of the next breeding season, culture her again to ensure that she’s clean before making plans to breed. 

Quick Tip: If you only have one or two mares to breed, it’s likely most convenient to haul them to your vet’s office to be cultured. If you have a barn full of broodmares, schedule an appointment for your vet to come check all your mares at your property at the beginning and end of breeding season.

Tip 2: Use light to regulate your mare’s cycle. You want your mare to foal out as early in the season as possible, so she needs to start cycling close to the beginning of breeding season. Whether you plan to flush your mare or breed her to carry her own foal to term, you’ll need to control the length of time her body perceives as daylight hours. 

The most obvious option to accomplish this goal is to bring her inside before dark and keep her under lights until around 10 p.m. You can use a timer or manually turn the lights back on around 5 a.m., then leave them on until it’s full daylight. Depending on the size of your breeding operation, you can either bring one mare into a stall with lights set on a timer or keep a group of mares in a lighted pen. Both strategies accomplish the same goal of shortening the period of darkness and causing your mare to begin cycling sooner.

Quick Tip: If you don’t have a space to bring your mare(s) inside under lights, you can purchase a mask designed specifically to regulate the amount of light your mare perceives without interrupting her turnout schedule. That way, your mare can stay outside and still get the amount of the light she needs to regulate her cycle. Light-blocking masks can also be helpful with a horse you need to separate before breeding, such as an older mare who can’t stay out with a herd. of broodmares. 

Mare with her head through metal stall door
If possible, it’s ideal for your mare to stay near the stallion’s location so the semen is fresh when she’s inseminated.

Tip 3: Provide your mare with the hormones she needs. When you’re preparing to breed a mare, whether she’s a recipient mare, a donor being flushed, or a mare that will carry her own foal, you’ll need to give her hormone supplements. Work with your veterinarian to develop a regimen including hormones to encourage your mare to cycle; hormones to make her ovulate on schedule; and progesterone (or synthetic progesterone) to keep her pregnant, even if it’s only long enough for an embryo to develop. 

Quick Tip: In most cases, it’s helpful to check hormone levels before breeding, then modify your regimen accordingly. For example, if you find your mare’s progesterone level is low, you’ll want to supplement her until at least 100 days after breeding to keep her levels high enough to maintain pregnancy. After that, a healthy diet will keep her hormone levels strong. 

Healthy for the Duration

Once your mare has been successfully inseminated, it’s important to keep her healthy throughout the pregnancy. In addition to key hormones early on, your mare may need vitamin and mineral supplements as she reaches the third quarter of the gestation period. This will help prevent her foal from developing deficiencies or bone problems while still in the womb. About 30 to 45 days before your mare’s foaling date, monitor her closely. When she’s close to foaling, using a foal-alert system can help ensure that you’re on-hand to help when she’s ready to foal. 

Tip 4: Know the semen that you plan to use. While your mare’s preparation plays a major role in the success of the breeding, some stallions have more delicate semen. In that case, you’ll need to inseminate very close to ovulation or consider using deep-horn insemination methods. The best way to ensure success is to have your vet palpate the mare frequently so he knows when she’s about to ovulate.

Quick Tip: You might think a larger semen sample would make it easier for your mare to conceive, but that’s not usually the case. In fact, a low-volume, highly concentrated dose offers the greatest chance for success. That’s because a larger volume often means there’s more semen extender, not more semen. 

Tip 5: Get everyone on the calendar. Coordinate with your veterinarian and the stallion’s owner to schedule insemination with fresh semen at the optimum time in your mare’s cycle. It’s always best to keep your mare near the stallion’s location so the semen is fresh. This prevents any unwanted mishaps if she ovulates sooner or later than anticipated. 

Quick Tip: Remember, even if your mare’s cycle appears normal from the outside, that doesn’t always mean she’s ready to carry a foal. Work with your veterinarian to prevent infection and check for any complications that could hinder her pregnancy before you attempt to breed. 


Thiago Boechat

Thiago Boechat first came to the U.S. from Brazil in 1993. He returned home to attend veterinary school at Universidade Do Oeste Paulista, but returned to the States in 2004. Since then, he’s achieved success at multiple NRHA major events, including the NRHA Futurity and Derby, and currently serves as ranch manager at Silver Spurs Equine–Oklahoma.