Knowing Signs of Approaching Foaling Useful for Horse Breeders

Expected birth date is an age-old question for horse breeders tending four-legged mothers-to-be as much as any proud parent. Most mares are bred naturally by scheduled breeding with the stallion or through artificial insemination.

Dave Freeman, PhD, Oklahoma State University Cooperative Extension equine specialist, said knowing the last breeding date and approximating the expected gestation length should get a horse manager in the ballpark of the expected foaling date.

"The normal gestation length of broodmares averages 338 to 345 days," he said. "Simply moving ahead 11 months from the last breeding should get you on the early side of expected foaling date."

One point of caution, however: gestation length will be variable between mares and even the same mare from year to year.

Knowledgeable horse breeders can take advantage of several conformational and behavioral changes in the mare that suggest the foaling day is approaching.

"Changes in the mineral concentration of the milk immediately prior to foaling can be monitored with commercially available kits that work on the same principles as water hardness check strips available through commercial outlets such as plumbing supply and home improvement stores," Freeman said.

Other changes in mares suggesting that foaling is approaching include:

  • A mare's udder fills two to four weeks prior to foaling, although this might not be as easily detectable in maiden mares. Additionally, mares may have filling and regression periodically through the last trimester;
  • Horse breeders may notice a change in tailhead conformation one week to one month prior to foaling. The horse's musculature relaxes, leading the abdominal area to drop down;
  • The mare's teats fill with milk two days to one week prior to foaling, although responses will vary from specific animal to animal;
  • Milk may drip from a mare's teats one day to one week prior to foaling, again with variable responses from one animal to another;
  • Secretions form wax-like beads on end of teats one to four days prior to foaling;
  • Changes in milk mineral content can be viewed about a day prior to foaling as the calcium concentration increases; and
  • The mare's external genitalia relaxes 12 hours to one day prior to foaling. Musculature under the tailhead relaxes, becoming soft and loose.

"It's important to remember that not all signs are seen in all mares and signs will differ in intensity and occurrence from maiden pregnancy to those following previous births," Freeman said.

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