The history of artificial insemination in the horse goes a lot farther back than one might expect. The earliest references of the use of artificial insemination in the horse come from Arabic texts in the 1300’s. It wasn’t until the 1700’s that the Italian physiologist Spallanzani documented scientific evidence on the use of artificial insemination in the horse, including the effects of cooling on stallion semen. During the 20th century artificial insemination has became widespread worldwide. This article will compare advantages and disadvantages to artificial insemination as it compares to natural service.
Brief Overview Of Equine Reproduction
Mares are seasonally polyestrous; in other words, they have regular fertile cycles during their breeding season, which begins in the spring, is in full force during the summer months and tapers off in the fall. During the winter months at our latitudes, the majority of mares stop cycling, the ovaries become inactive and, since they are not having ovulations, they are not fertile. This period of ovarian inactivity is called the winter anestrous. Between the winter anestrous and the regular breeding season is the spring transition, during which the ovaries become increasingly active until eventually the first ovulation of the new season occurs. Similarly during the fall transition, the ovaries become less active as they enter winter anestrous.
During the regular breeding season, mares generally have a 21 day cycle. During this 21 day period, mares are “in heat” (i.e. in “estrus” and are sexually receptive to the stallion) generally for 4 to 6 days. A dominant follicle (where the egg develops) will grow until it finally ovulates, bursting open to release the egg. Following ovulation, the mare will soon go out of heat, usually within a day. In order for fertilization to occur, live spermatozoa have to be present after the egg is released and before it dies. Approximately 15 days after ovulation, if she is not pregnant, the cycle will start again.
Advantages of artificial insemination
• Access to stallions: The only breed registry that continues to not accept artificial insemination is the Thoroughbred. Most, if not all, of the other registries allow the use of artificial insemination, including the use of shipped cooled and frozen semen. This allows access to stallions all over the US and Canada, and in the case of frozen semen, international access as well. This increased availability of stallions is the main driving force for artificial insemination.
• Mares can stay home: There is always some risk of illness and injury when mares are shipped and stabled away from home. Keeping the mare home eliminates these worries, as well as the shipping and boarding costs.
• Stallions can breed more mares: With natural service, a stallion can breed one or two mares a day. There are, however, enough spermatozoa in a single ejaculate to breed several mares. With artificial insemination, each collection can be divided into several insemination “doses” so several mares can be bred in a single day and many more mares can be bred in a season compared to natural service.
• Safety issues: When dealing with an experienced, well mannered stallion with good libido and an experienced broodmare that shows a strong heat, natural service generally proceeds rather smoothly. However, there are numerous other scenarios that can create problems. Inexperienced stallions literally have to learn how to mount a mare and, in their man-made environments, they don’t get much practice. Mares that haven’t been bred before can be difficult. Some don’t show heat well in the first place. Even if they do, they may panic when the stallion mounts. Mares in foal heat, which occurs 7 to 11 days post partum, may not show heat as well, especially if the mare is overly concerned about her newborn foal. Some mares have “silent heats” and never show strong signs of receptivity to the stallion. These difficult situations create a much greater risk of injury to all involved, the stallion, the mares, and the handlers.
• Less disease transmission: Natural service exposes the stallion, and therefore the mares he covers, to greater chances of contracting and spreading sexually transmitted diseases.
Disadvantages of artificial insemination:
• Special stallion equipment: Not much equipment is required for natural service. For light duty, all that might be necessary is a tail wrap for the mare and supplies to wash the mare and stallion. For busier stallions, other supplies need to be available, such as restraint devices for the mare (leg straps, breeding hobbles, back feet boots, twitch), a breeding roll to protect the mare, and a breeding pad for the stallion to hold onto.
Obviously semen collection equipment is required for artificial insemination. This includes an artificial vagina, measuring and storage glassware, semen extenders, microscope, and an incubator. Shipped cooled semen requires special shipping containers that maintain the proper temperature prior to insemination. Frozen semen requires more processing equipment, such as special centrifuges to concentrate the semen, straws to store the semen, a special freezing device, and liquid nitrogen containers for shipping and storage of semen.
• Special mare equipment: Shipped cooled semen doesn’t require much more than a few insemination items. Frozen semen requires a water bath to thaw the semen properly. The water bath doesn’t have to be expensive or high tech but it does need to be effective (i.e. maintain a specific water temperature).
• Timing of insemination: Natural service generally has the luxury of having the mare and stallion at the same place. If the mare needs to be bred, generally it can be arranged. With shipped cooled semen, the semen has to be ordered and shipped. Most stallion managers require the semen order to be placed the day before it is collected. Cooled semen is usually sent by Federal Express or UPS and doesn’t arrive until the day after collection. The goal is to inseminate the mare close to but not after ovulation, so that live spermatozoa are in the oviduct when the egg is released. This requires close monitoring of the follicle’s development to help predict when insemination will be needed.
There are other issues that complicate this timing issue further. Many stallion breeders restrict their collection days to Monday, Wednesday and Friday or to every other day. Weekends and holidays can be difficult to work around as well. With frozen semen, we again have the luxury of having the semen at the same place as the mare, in this case in a straw rather than the stallion. But frozen semen creates different challenges. The longevity of the semen after thawing is dramatically reduced when compared to natural service or shipped cooled. Thus, the insemination timing is narrowed to a twelve hour window, anywhere from six hours prior to ovulation to six hours post ovulation. This requires even closer monitoring of the mare’s follicle, especially when she gets closer to ovulation. The close monitoring of the mare’s follicle required for artificial insemination is facilitated by the use of ultrasound, which provides predictive details concerning ovulation.
In summary, although artificial has many advantages, it does require more technical equipment, training, and skills. It also requires closer monitoring of the mare’s cycle to predict when ovulation is going to occur and when the insemination needs to be performed.
Copyright © 2008 The NW Horse Source, LLC
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