Spring is here and we often think about breeding season as new life pops up everywhere. The first question to ask isn’t, “Will my mare breed?” but “Should my mare be bred?” It’s possible you would be happier with adopting or rescuing an unwanted horse that you can ride now rather than breeding and waiting for that foal to grow before riding. Next it is important to start with the overall health of the brood mare and then get a breeding soundness exam, both of which should be done the winter prior to a planned breeding.

When you are discussing a general physical examination with your veterinarian, consider the following:

  • Is she in good body condition, is she too heavy or too thin?
  • Is she current on her vaccinations? Which ones does she still need?
  • Check her parasite load – what are the current fecal egg counts?
  • Are her hooves in good condition?
  • Does she have a current negative Coggins?
  • Are there any conformation defects or genetic abnormalities that could potentially be passed to offspring?
  • Is she too young? Is she too old? Is she prone to producing twins? Does she have a history of abortion.

Once all these questions have been answered satisfactorily, you can move on to a breeding soundness exam. This is especially important with older mares and those that have had problems getting pregnant in the past. Your veterinarian will start with a physical examination of the reproductive anatomy – are there any conformational issues with the perineum (rectal and vulva region).

They will do a rectal palpation to assess any potential abnormalities in the ovaries, uterus, cervix, vagina or bladder and estimate where the mare is in her estrous cycle. Depending on discoveries in one or more of these areas, the veterinarian or stallion owner may request samples be collected for laboratory analysis, a uterine culture or cytology to check for pathogens or inflammation and/or a biopsy to evaluate the uterine tissue, in order to predict the mare’s ability to become pregnant and carry a foal to term.

If the physical and breeding soundness exams give a healthy result, then it is time to establish your mare’s estrous cycle. It will tend to average 21 days but she will only be receptive the first week or so of the cycle. It is helpful to have the mare palpated to determine follicle size so you can estimate time of ovulation. You can also use a tease stallion to determine when (if) your mare is in heat. Signs of heat to watch for are winking of the vulva, tail raising, frequent urination and squatting into a breeding position. If the mare pins her ears back, clamps her tail down or acts aggressively toward the stallion then she is not receptive (not in heat).

Once you understand the estrous cycle of your mare, decide when and how to breed. Do you want to breed on the first heat or catch the next one? Do you want to breed by live cover or artificial insemination (AI)? If by AI, will you be using fresh, cooled or frozen semen? What is the collection schedule for the stallion you are using? Do they ship overnight or counter to counter? Fresh semen often has the highest viability (fertility) but isn’t always convenient if the stallion isn’t on or near the farm. Cooled semen should be viable for 36-48 hours but that can depend on the stallion used. Frozen semen is sometimes more complicated to manage because insemination must take place within 6 hours pre- or post-ovulation. When breeding by AI, induce ovulation by using a commercial hormone injection and timing insemination around that injection to ensure a successful ovulation. You can have a veterinarian do an ultrasound in about two weeks to confirm pregnancy or whether a second breeding cycle should occur. Individual mares will have their own gestation idiosyncrasies but the average gestation period can range from 320-360 days.

Daily Nutrient Requirements (1,100 pound mare)

Nutrients RequiredEarly to Mid-GestationLate GestationLactating Mare
CP (pounds)1.411.73.0
DE (Mcal)161828
Ca (g)203556
P (g)142636
Vit. A (1,000 IU’s)153030
University of Nebraska Cooperative Extension EC95-272-B

You should always be aware of your horse’s body condition but it’s especially important in the pregnant and lactating mare. Mares in marginal condition (thin to poor, <5) seldom have enough fat stored to reproduce efficiently, support the embryo full term and/or produce milk efficiently if they deliver a viable foal. Mares in the obese range of 8-9 won’t necessarily have foaling problems or difficulty rebreeding but it won’t provide you with any reproductive advantages either. It’s also possible that a mare with a heavy crested neck or bulging fat pads could have an insulin issue or other systemic illness that may negatively affect reproduction. Ideally, maintain your mare in the 5-7 range (moderate to fleshy) using a proper ration for her breeding/activity stage in order to meet her daily nutrient requirements. In the last trimester, her nutrient requirement will increase a great deal because the foal is growing faster and she has to meet her own needs as well as that of the foal. The mare won’t necessarily need more total feed but the concentration of protein (CP), energy (DE), calcium (Ca), phosphorus (P), and vitamin A should increase. By this point the mare should be getting 1.5-2% of her body weight in feed per day, through concentrated feedstuffs as well as good quality hay.

A horse which scores a BCS 5 is the industry standard and baseline for which most recommendations are made. This horse’s ribs are not visible but are easily palpable upon inspection. This horse has a blended appearance and smooth lines are created by fat cover. This horse’s back is level and does not peak at spinal processes.

A horse with a BCS 6 is considered fleshy. This horse may start to develop a crease along its back due to fat deposits along the spine. Fat deposits covering the ribs, along the withers and behind the shoulder will feel spongy.

A horse with a BCS 7 is very fleshy with fat deposits that start to interfere with palpating structures. Fat will feel spongy in all areas. Individual ribs may be difficult to feel at a BCS 7. The horse’s back will likely develop a crease due to fat deposits along the spine.

When it’s time for your mare to foal, ensure she has a clean, dry, safe place to do it. Ideally a foaling stall bedded with straw that is 12 x 18 feet should give plenty of room; outside is ok too as long as the weather cooperates. A spring foal rarely waits for our convenience, plan ahead so you don’t have to stay up all night for days on end. See the March 2021 Leading Rein newsletter for the stages of foaling and how to care for your new foal.

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