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Horse Breeders May Need To Increase Heat Detection Efficiency:

Last Modified: February 19, 1999

Horse breeders who use heat as the sole indicator of when it is time to breed mares may risk operational profitability unduly. Broodmares that are not settled within one or two breeding cycles force the horse owner to incur undo labor, feed and others expenses associated with having an open mare late in the breeding season.

"Mares vary in the level of estrous behavior they exhibit, and may change as they proceed through the breeding season. Thus, using heat as the sole indicator will have its limitations," cautioned Dave Freeman, Oklahoma State University Cooperative Extension equine specialist.

Most mares are in estrus for a three-to-seven-day period every 21 days of the breeding season. It is typical for mares to not show estrus until they perceive long day-lengths.

"As such, you expect open mares to starting showing estrus as day length begins to lengthen in the spring, and continue to cycle until bred or until late fall when day length begins to shorten," Freeman said.

A long-time common practice has been to artificially extend the day lengths of fall and winter by housing open mares under lights that extend "daylight" to 16 total hours per day, thus causing mares to begin heat earlier in the year.

"This practice helps in planning for 'early' foals, and in spreading out the number of mares to be bred across the season instead of allowing all mares to group up in the middle of the breeding season," Freeman noted.

Mares ovulate the first day to day-and-a-half of estrus, with conception rates being highest when bred between the time frame of 36 hours prior to the time of ovulation.

"This is why it's common to breed mares every other day once they shows signs of heat," Freeman said. "Breeding more than this may be wasteful in terms of stallion use, and some feel that breeding too often may increase the potential for bacterial infections in the mare."

Freeman said that since timing and number of breeding attempts are so critical to overall operational success, palpation and ultrasound should be used in addition to teasing techniques to ensure efficiency.

"This is especially true for those persons scheduling mares to be inseminated through use of cooled semen or appointment-type breedings where the mare will not receive more than one dose of semen on a cycle," Freeman added.

Palpation by a veterinarian knowledgeable with mares and changes in their reproductive tract provides evidence of physical changes, such as size of a follicle, that suggest ovulation will occur within the following day.

Ultrasound can provide further evidence of the status of a mare's reproductive tract. Ultrasound allows for a visual "picture" of the reproductive tract, which aids in the accurate measurement of indicators of approaching ovulation such as follicle size and shape.

"It is possible to settle most mares by breeding on one cycle, or at least two, by using the combination of teasing, palpation and ultrasound," Freeman stated. "If the majority of mares are not being settled, then the horse owner incurs breeding-related expenses that he or she shouldn't, thereby causing the operation to lose money it would otherwise have."

The above article has been provided courtesy of
Oklahoma Cooperative Extension Service.