Signs of Equine Pregnancy

Early detection of equine pregnancy is important for horse breeders and enthusiasts alike to ensure chances to feed, supplements, turnout and veterinary care can be made at the appropriate times. Knowledge of pregnancy status is also important for breeding contracts and sale situations.

  1. External Signs

    • There are no external signs in early pregnancy. In fact, other than weight gain and possible signs of fetal movement at mid to late pregnancy, there are no visual cues until the last month or so before delivery. In the last month prior to delivery, a pregnant mare will begin to "bag up" as she develops a milk supply. As she moves closer to delivery, the foal will drop, causing her abdomen to become more pronounced. Pelvic changes as ligaments soften are present but very hard to detect. Relying on external signs is not recommended.

    Ultrasound Detection

    • Ultrasound provides the earliest confirmation of pregnancy, potentially as early as 10 days after conception, although most vets do not perform an initial ultrasound before about two weeks after breeding. Based on the shape, size and location of the chorionic vesicle, approximate gestational age of the embryo can be determined. Other reasons for ultrasound include twin detection and verification of fetal heartbeat, which can be observed at approximately 23 to 24 days gestation.

    Palpation

    • Before the availability of ultrasound, palpation of the uterus by rectum was the typical method of pregnancy detection. Palpation is still the detection method of choice for many breeders. Changes in the tone and shape of the cervix take place beginning at 16 to 17 days and continuing through delivery. Approximate aging of the pregnancy can be made based on the size and shape of the embryonic vesicle, first detectable at about 20 days. From day 60 to 200, palpation can be difficult, but after day 200, results are near 100 percent accurate as the fetus can be felt through the uterine wall.

    Pregnancy Testing

    • Hormonal testing (through blood or urine) remains the definitive test of equine pregnancy. Testing prior to 40 days is unreliable. However, the most reliable early detection is with the eCG blood test (92 percent accuracy at 42 days). One shortcoming of the eCG test is the result remains positive in the case of fetal death. Blood testing for estrogens--a highly reliable form of testing--is not available until the levels become elevated after 150 days. Testing for estrone sulfate, detectable in any bodily fluid, is another alternative, available after 60 days. Choice of test will depend on the number of days since the breeding date.

    Warning

    • Failure to detect a pregnancy prior to foaling can have serious implications, particularly if the mare typically grazes fescue fields. Fescue is known to prolong gestation and prevent milk production, which can lead to life-threatening complications in mare and foal. Eliminating all fescue from the pregnant mare's diet at least 90 days prior to foaling will circumvent these problems.