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Equine Health Resource

Pregnancy, Mare Seems Abnormally Large

Code Orange - Call Your Vet at Their First Available Office Hours

Code Orange - Call Your Vet at Their First Available Office Hours

  • You have any concerns about the late-term pregnant mare.

Inexperienced breeders are commonly concerned about the seemingly excessive size of their pregnant mare.

They are often worried that there is something wrong or that their mare is carrying twins. Mares are individuals, and some may seem (and are) huge as they enter the final months of their pregnancies. Most of their gain in weight occurs during the last three months of the pregnancy.


Consider the mare’s last breeding date. Average gestation length for mares is 335 days, but there is great variation depending on many factors. 325-365+ days would be considered a normal range. Note: Generally, late-term mares that seem too large are not likely to have twins. The total weight of two twins is usually smaller than one singlet. In addition, most mares with twins abort before term.

Assess your mare’s general health using the Whole Horse Exam (WHE), paying particular attention to the degree of udder enlargement, the presence of absence of milk dripping from the teats. Check the vulvar area for “softening” or discharge.

If the results of the WHE are normal, and there is no vaginal discharge or premature lactation she is probably fine. Keep in mind that many mares in their last trimester of pregnancy have slightly elevated resting heart rates (48 BPM).

If your vet has not previously examined your mare during gestation to determine whether the pregnancy is high-risk, you should contact them to discuss your findings and concerns.


Your vet assesses the late-term mare using rectal palpation and ultrasound, as well as ultrasound through the mare’s abdomen. There are also several hormonal tests that can help verify fetal well-being, although they are not commonly used.

Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health

Author: Doug Thal DVM Dipl. ABVP


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