While there are common signs many mares display when pregnant, the most effective and reliable method is examination by your veterinarian. To determine pregnancy status, they will select from several veterinary tests available, which we outline in this article.
Most commonly, transrectal ultrasound is used to confirm a positive pregnancy. Transrectal ultrasound not only verifies the status of the pregnancy, but can be used as early as 10 or 11 days post-ovulation. A transrectal ultrasound provides the following information to your veterinarian:
Confirmation of whether or not your mare is in foal Estimated foaling date, which is particularly helpful if breeding dates are unknown
Visualisation of the foetus and its heart beat at 24 days or more following ovulation In the early stages of pregnancy, problems can arise that place your mare or unborn foal at risk.
Transrectal ultrasound also indicates any problems with the pregnancy, which can be dealt with immediately by your veterinarian.
There are several blood tests that can be performed by your veterinarian to determine pregnancy status if transrectal ultrasound isn’t used.
While some blood tests are more favourable than others for accuracy, each allows mare owners to test for positive pregnancy at different stages of gestation. These include:
Day 12-14: measure progesterone levels
Day 35-140: measure equine chorionic gonadotropin (eCG) levels
Day 80: measure oestrogen levels
At Day 12-14, progesterone levels will often remain elevated in pregnant mares for the duration of their pregnancy. However, elevated progesterone levels aren’t a reliable indicator of pregnancy in all mares. If progesterone concentration is less than 1 ng/ml, the mare is likely not pregnant.
Equine Chorionic Gonadotropin (eCG)
Following Day 35, eCG levels will rise and remain elevated until Day 100-140 of gestation. While elevated eCG levels are a reliable indicator of a positive pregnancy, this test can only be performed between Days 35 and 140 post-ovulation.
At Day 80, oestrogen starts being produced by the foetus and the placenta. An increase in conjugated or total oestrogen levels indicates a positive pregnancy. However, oestrogen levels can’t be tested prior to Day 80 of gestation.
For many, breeding a mare represents a sizeable investment in time, money and resources.
A qualified equine reproductive veterinarian will be able to give you the most definitive answer on your mare’s pregnancy status, so you spend less time guessing and more time preparing for the arrival of a healthy newborn foal.