8 Steps for Breeding Your Mare

Last Updated on February 24, 2022 by Allison Price

Use a structured approach to managing your broodmare for the best chances of a successful pregnancy

Sperm, meet ovum. If breeding horses was as easy as that, there wouldn’t be an entire branch in veterinary medicine devoted to horse reproduction. Even virile stallions and in-heat mares don’t always produce foals. If your broodmare collection includes maiden, older, or subfertile mares, there are more things to consider and track to ensure a successful breeding season. You can cultivate success in the spring by taking a systematic, stepwise approach to managing each mare with your veterinarian team.

First: Take into account the mare’s overall health

Margo Macpherson, DVM, MS, Dipl. Margo Macpherson, DVM, MS, Dipl. ACT is a professor of Large Animal Clinical Sciences at Florida’s College of Veterinary Medicine in Gainesville. There’s no single method for managing broodmares; each mare must be assessed individually.

Before you focus on the mare’s reproductive health, it is important to assess her overall wellbeing. Is she healthy? Are her hooves in great shape? Are there any vaccinations she needs? To check for parasites, does she require a fecal eggs count? Are her weight levels too high or low? Is she due for a dental exam

Karen Wolfsdorf, DVM, Dipl. ACT is a field veterinarian and reproductive specialist at Hagyard Equiline Medical Institute’s McGee Fertility Centre in Lexington, Kentucky. She says that one of her most important first observations is the mare’s Henneke Body Condition Score (BCS). Broodmares should be able to score between 5 and 7 on the 1-to-10 scale before they are allowed to breed.

Wolfsdorf says, “I like being able to feel the ribs but I don’t see them.”

Breeding Your

She also mentions that she looks out for protruding fat pad, a cresty, or any other abnormalities that might indicate that the mare may have pituitary intermedia dysfunction (PPID or Equine Cushing’s disease),, insulin dysfunction or another systemic illness that could impact the reproductive system.

She also considers the mare’s past breeding, including problems getting pregnant, Endometritis (inflammation in the uterine lining),, and abortion.

It is important to be familiar with the specific requirements of the chosen breeding shed if the breeding will take place under live cover. Wolfsdorf, for example, says that some breeding sheds require vaccinations against rhinopneumonitis (herpesvirus-1) which veterinarians typically administer three to three months before the breeding to protect the stallion. Wolfsdorf advises that owners be aware of the mare’s history of vaccinations and ensure she is up-to-date on vaccines for diseases in this region.

The American Association of Equine Practitioners recommends that mares be vaccinated against herpesvirus-1 at three, seven, and nine month gestation to reduce the chance of spontaneous abortion. Some high-traffic farms may allow veterinarians to administer the herpesvirus vaccine every other month, but this is not a recommended practice.

Step 2. Schedule an examination of your breeding soundness and address any issues

Wolfsdorf says that getting a mare pregnant requires a partnership between the broodmare owners and the veterinarian. A breeding soundness examination is a reproductive exam for broodmares. It helps to identify and manage potential problems.

Macpherson states that she is mindful of the client’s financial situation and will list all options for her clients to help them make informed decisions about which evaluations they should perform. A mare may only require a breeding soundness test if she fails to conceive within the first two to three attempts.

Macpherson states that a breeding soundness assessment is more important for mares with difficulties in pregnancy or older or middle-aged maiden horses. “A breeding soundness evaluation is intended to help the owner make informed decisions and to solve problems.

Wolfsdorf examines broodmares with no breeding-related problems. He starts by looking at the mare’s reproductive anatomy. This includes the perineal conformation, which involves the vulvar lips and/or vestibular-vaginal fold, and/or the horse’s cervix. Poor perineal conformation can lead to reproductive tract contamination by feces, air and microbes. This can be prevented and the possible infection may be avoided by having the veterinarian sew the vulvar lips together (a procedure known as a Caslicks). The stitches are then removed for breeding and foaling.

A transrectal palpation will be performed as part of the exam. These tools are used to determine the mare’s stage in her estrous cycle. These tools can also be used by the vet to check the mare’s ovaries size and function and to identify any abnormalities in her uterus or vagina.

Macpherson states that she does an ultrasound exam before she breeds any mare she is evaluating. She says that while the tools of palpation are important, there is so much more that can be seen with an ultrasound that can have an impact on breeding management.

Wolfsdorf says that abnormal cases often require ultrasound and palpation to determine the next steps. She says, “What we see in her abdomen will determine what type of culture or cytology we might want to do” to confirm and identify the pathogens.

She said that she performs this procedure most often in mares with a “baggy and saggy” type of uterus. This includes older broodmares, foals that have had multiple foals or those who have had endometritis. Because of poor uterine clearance, these mares may be more susceptible to breeding-induced endometritis.

A biopsy of the endometrium adds an additional piece to the evaluation. The veterinarian will examine a small section of the endometrium to check for any abnormalities. This includes inflammation, scar tissue around the glands and vessels, as well as dilated lymphatics. The vet can use the endometrial tissue to predict the likelihood of a mare becoming pregnant or keeping the pregnancy alive.

A veterinarian can conduct a hysterocopic examination on a mare to get more information. This involves inserting an endoscope in the uterus to check for foreign bodies, adhesions or fungal/bacterial plaques.

Your veterinarian can use the information from your breeding soundness exam to help you recommend management techniques or treatments for breeding.

Step 3: Start the mare riding.

After your veterinarian has treated any reproductive problems, it is important that your mare is normal in her cycle before you breed. Mares are seasonally polyestrous. This means that they cycle and become heat during long days, such as the spring and summer. Some mares can cycle all year.

Breeders, particularly Thoroughbred breeders try to get their mares pregnant late in winter or early in spring to foal earlier in the year. You might have to get your mare to cycle in winter when she is in anestrus, which is a time of no estrus. Breeders can use artificial lighting and/or hormone therapy to get mares to cycle. (For more on getting a mare to cycle, see TheHorse.com/166159.)

As nights become shorter and daylight increases (or as artificial lighting or hormone therapy takes effect), says Wolfsdorf, melatonin levels in the body lower, prompting gonadotropin-releasing hormone (GnRH) secretion.

She explains that GnRH will then travel to the anterior pituitary, where it functions to release FSH and LH. These hormones stimulate follicular growth by influencing the ovaries.

The mare creates and regresses the follicles, until a dominant one forms that produces enough estrogen for a strong first estrus (also known as heat).

Wolfsdorf explains, “Then the luteinizing hormone induces (in the dominant foollicle) ovulation.” “The mare transitions from anestrus to ovulation, when she isn’t cycling through a period of about 60 days before (this) first ovulation.”

Step 4 – Track the mare’s estrous cycles to determine when she’s ovulating

The mare’s estrous cycle is 21 days long, but she will only become pregnant and open to breeding after five to seven days. Ovulation takes place during the last 24 to 36 hour of behavioral estrus.

Macpherson says, “Breeding close to ovulation should always remain the goal.”

It is crucial to know when a mare is in heat in order to determine when the veterinarian should begin examining the mare. This will help determine when the veterinarian should begin examining the mare’s follicles. This can help determine ovulation time and whether artificial insemination is used.

Macpherson employs a teasing horse to find signs of heat in the mare. This includes vulvar “winking,” interest in the stallion (especially when head-to-head contact is made), vulvar “winking,” squatting into an open breeding position (receptivity), tail-raising and frequent urination. A mare that is not responsive to a stallion’s attention can display a few signs, such as a pinched ear, tail-clamping and aggression toward the stallion. TheHorse.com/14717 has more information about teasing.

5: Decide when to breed your mare

After a mare starts cycling, her owner must decide whether to either breed her in the first heat, Wolfsdorf says, or wait for the subsequent heats which have higher pregnancy rates. However, if you are breeding for a Thoroughbred racehorse, it is important that the foal be born close to January 1st, which is the breed’s official birthdate.

The breeding method, whether it is live cover or artificial intelligence, also dictates the timing of your babies. Artificial intelligence (AI) is partly based on whether the semen is fresh, frozen, or cooled. Because it isn’t processed, fresh semen has the highest fertility rate. However, it cannot be transported and must only be used immediately. Colded semen viability varies by stallion, but it is generally good for between 36 and 48 hours after collection. These methods should be used by the veterinarian to prepare the mare for ovulation within 24 to 40 hours after insemination (see step 6). Frozen Semen is more difficult because insemination must take place within six hours before or after ovulation. This leads to lower success rates.

Wolfsdorf says that cooled semen requires you to know when the stallions will be collected and shipped. Also, whether they are shipped counter-counter (by commercial plane) or FedEx overnight. This will allow you to… time when your semen is ready by using ovulatory-inducing drugs.

6: Use veterinarian technology to time breed with ovulation

A veterinarian can “short-cycle” a mare off her first heat after foaling to help her get pregnant faster and/or track her cycle better. This is also known as foal heating. If you are breeding your mare back, this will be a great way to do so. To bring her back to heat, the veterinarian will administer exogenous prostaglandins that are not derived from mares. This reduces the 14 to 17-day period between estrus and ovulation. The mare’s return to heat will depend on the size of her follicles at the time she is given prostaglandin (usually six weeks after ovulation).

Wolfsdorf says that if she has a 25-millimeter-long follicle on the ovary, it will take her four to five days to become heat and three to four days to ovulate. “However, if she has a big 35-millimeter follicle on her ovary when you give her prostaglandin, if you get rid of the corpus luteum (CL, the progesterone-producing structure formed after the follicle releases the egg), that mare comes into heat in two to three days and ovulates in (another) two to three days.”

A GnRH analog can help mare owners to predict when they will breed. Wolfsdorf says that an ovulatory-inducing drug is a “insurance policy” to ensure that mares ovulate when they want.

Macpherson recommends that a mare be inspected daily while she is in estrus. She says, “I have learned that I do a better job when I am able to spend a lot of time looking at the mare.” She says that a mare in heat and a mare in heat, or a mare in heat and a mare in early heat can have very different results. “With a frozen mare of semen, we often look at her up to three times per day and learn a lot each time.”

Once you have determined the best time to breed, your veterinarian should oversee the live coverage and artificial fertilization.

If there is fluid in their uterus I consider it a sign that they are physiologically impaired.Dr. Margo Macpherson

7: Promote uterine clearance in mares with problem mares

Her body responds to a natural inflammatory reaction when a mare is bred. This response occurs usually within 12 hours of the breeding. It helps rid the uterus from dead sperm, inflammatory cell debris and other contaminants. Macpherson says that mares are often bred under natural conditions and her reproductive tract is able to clean up after these multiple breedings.

Breeding in a man-made situation can affect the clearing process, resulting in persistent post-breeding-induced endometritis.

“If they have fluid inside their uterus, it’s an indication that something is physiologically impaired,” Macpherson says. This could be a problem with uterine contractility or uterine drainage.

A mare that has had multiple foals or a stretched uterus might have trouble with the natural clearing process. This is because gravity is not always on their side. Young mares’ uterus is higher than the pelvis so it can remove contaminants more easily through the cervix and vagina. If a mare has had multiple foals, her uterus may hang below the pelvis, which can affect uterine clearance. The fluid must move “uphill” to reach the pelvic floor.

Wolfsdorf suggests that broodmare managers turn out recently bred mares so they can move about.

The uterus can be contracted by oxytocin administration, lavage of the uterine, and acupuncture. Misoprostol and Buscopan, along with other medications, can relax the cervix, which can be beneficial for older maiden mares who have tight cervices that block drainage.

Step 8: Check for pregnancy

After your mare has been bred and is healthy, it is time to confirm that she is pregnant. A veterinarian can confirm pregnancy by using ultrasound within 14 to 15 days after ovulation. Your veterinarian will be able to diagnose and treat any possible reasons the mare may not be pregnant before she is bred again.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!