Stages of Pregnancy in Horses

Horse breeding is a specialized area of animal breeding. Breeders observe standard gestation periods in horses, though individual breeds can experience atypical gestation periods as well. The foaling period is also rarified among animals and requires knowledge about horses and their anatomies. Any human interference in the process can irreparably harm both the mare and the foal. Foaling usually occurs in three stages that often take hours to complete.

The average gestation period for horses ranges from 335 to 340 days. This is by no means the only standard that is observed in all horses, though. Sometimes individual mares experience different types of pregnancies. But breeders have observed that gestation periods can typically range for 11 months. What is standard, though, is that foaling that occurs before 326 days is considered premature, while foaling that begins at 310 days is considered an abortion.

Early signs of foaling begin when the udder develops at 2 to 6 weeks before foaling. The milk lets down into the teats at 4 to 6 days before partuition (actual delivery). Some horses might also experience dripping colostrum, which breeders save later for the foal. 1 to 2 days before foaling, the mare also experiences waxing at the ends of her teats. The muscles in the pelvic region will relax prior to partuition, and become progressively more relaxed during the last 2 weeks of gestation. Once this occurs, the mare enters partuition, which occurs in three stages.

The first stage of partuition begins 1 to 4 hours before delivery. This is when the mare's uterus contracts and the foal is positioned for delivery. During this period the mare will experience erratic behavior. She will become restless, pace the stall, paw the straw with her hooves and switch her tail. She will stand and lie down, eat irregularly, stopping in mid-chew, and will experience sweating in her flanks and frequent urination.

Stage 2 is when the actual delivery begins. This is the most critical phase of the delivery, of course, because the mare will often deliver on her own. Breeders state that helping a mare deliver is unnecessary and could even harm the animal because she will become anxious and restless when there is interference. During the delivery, the mare will experience extreme contractions and will lie down in the straw. At this point the water bag appears and then breaks, setting the stage for the foal's appearance. After the mare delivers the foal, blood is delivered through an umbilical cord. It is critical at this point that the cord not be broken because this is a process that helps increase the foal's health. If the mare is frightened or disturbed, she will stand and likely break the cord. Stage 2 ends when the cord breaks, and the foal is now physically independent of its mother.

The third stage of partuition begins with the delivery of the placenta. The placenta is usually ejected from the mare's womb 3 to 4 hours after delivery. Breeders then check the placenta. The placenta can be used to detect whether the mare is experiencing uterine infection and will determine the overall health of the mare.