Written By Dr. Kris Hiney

While breeding season may be the last thing on anyone’s mind at this time of year, it will be coming soon. Now is the time to ensure that your mare or stallion is going to be at their optimal reproductive efficiency. While much of a mare’s or stallion’s fertility depends on other factors such as age, condition of reproductive organs, etc., there are some basic management steps we can take to ensure that as few cycles of inseminations are needed to get a mare pregnant. Multiple breeding attempts can quickly outstrip the original stallion breeding fee and be a significant cost to the mare owner. Often we forget that every shipment of semen may be an additional cost, followed by extra veterinary fees, mare board, etc. Therefore it is in the mare owner’s best interest to have her in optimal condition before the first breeding attempt ever occurs.

So how do you prepare your mare and stallion in January to begin breeding anywhere from February to mid-summer? The easiest place to begin is to look at your horse’s body condition score. For a mare, we want her to be at a body condition score of at least 5 or 6 (see “Too Fat, Too Thin, or Just Right”). A mare in this condition would be a moderately fleshy mare whose ribs are covered by fat, has evidence of fat deposition behind her shoulder and over her tailhead, and whose back is level. Mares that are a higher condition score than that may still have no problem getting pregnant, but are unnecessarily obese. This may result in more wear and tear on her joints. Additionally, as there is no increase in reproductive efficiency, maintaining a mare in too high of condition may just be a waste of feed costs. Furthermore, if she has chronically been obese with localized fat deposition, she may even be at risk for metabolic syndrome or insulin resistance (see Equine Carbohydrate Disorders, Part 3: Metabolic Syndrome).  If your mare is diagnosed with metabolic syndrome, it is important to correct her metabolic profile and manage her carefully through the breeding season. Altered hormonal profile can impair her ability to become pregnant and certainly extra weight in a laminitic mare may increase her level of pain.

If we look at the opposite condition and the mare is too thin, she will need more cycles to settle compared to a mare at adequate condition. She also may take longer to return to normal cyclic activity following winter anestrous (when mares cease to cycle due to the shorter day length). Thin mares’ conception rates may be lower, and if she foals in a thin condition, she may take longer to begin cycling again. With so many negative effects of trying to breed a thin mare, one of the easiest ways to increase reproductive efficiency is to put weight on your mare!

Stallions also use more energy in the breeding season due to the increase in their activity levels. Stallions which breed mares in an intensive live cover breeding system will of course need more energy than a stallion which is bred only once every other day. Stallions which are more extensively used would have energy requirements similar to a light to moderately exercising horse, and their maintenance requirements will also be elevated (see “Energy for Work”).  Typically, stallions are simply more active during the breeding season as they exhibit their normal sexual behavior. Ideally, stallions should be maintained in a body condition score close to 5 throughout the breeding season.

Beyond just meeting a stallion’s energy requirements, feeding of Omega-3 fatty acids may help improve his reproductive efficiency. In a study by Harris, et al, published in 2005 in Animal Reproduction Science, stallions supplemented with dietary Omega-3 fatty acids increased their daily sperm output.  Furthermore, there was an increase in morphologically normal sperm in the supplemented group.  The greatest response was seen in the stallion with initially the most morphologically abnormal sperm. In this study, one stallion who was considered to be a “poor cooler” improved his post cooling progressive motility from 23 to 38% in a 48 hour test cool. Therefore, supplementation of Omega-3 fatty acids may be a valuable tool in improving the reproductive characteristics of sub-fertile stallions.

Basic guidelines for increasing body weight and condition in horses are really no different for the broodmare or stallion than in other classes of horses. The quicker the gain is needed in the horse, the larger the increase in calories which must be offered daily. If you only have two months to get your mare in condition, you need to increase her energy intake by 30-40% to increase her body condition score by one number. If we have three months, which may be more realistic, the energy requirements increase by 20-30%. Remember, however, if you are trying to accomplish weight gain during the winter, she may also have an increase in energy requirements due to her need to thermoregulate. This will make weight gain more difficult. To add calories quickly to the diet, look for a fat-added feed that will be digested quickly and efficiently.  Remember that fat offers 2.25 x the calories that will be in grains which consist primarily of simple carbohydrates. Fat will also disrupt the metabolic profile of the horse to a lesser extent than a diet high in sugars and starches.

Of course, beyond caloric intake, always ensure that your breeding horses are consuming a complete balanced diet in respect to all nutrients, have good health care and are suitable candidates for breeding. Breeding horses is a big responsibility in terms of the care and well-being of the mare, stallion and the subsequent offspring.