There are several ways to diagnose pregnancy in the mare:

  • Ultrasound scan
  • Rectal palpation
  • Blood test

Ultrasound scan

The most common method of diagnosing pregnancy used by vets is ultrasonography. Timing for this is crucial. There are several important factors to consider:

  • When was the mare either inseminated or covered
  • When she ovulated

These two pieces of information are important as these can change the timing of the first ultrasound scan by several days. 

  • The first scan is usually performed 14-15 days after ovulation (16-17 days after insemination).
    • The reason for the difference in these dates is because the mare usually ovulates 1-2 days after insemination/covering at the end of her oestrous cycle.
    • This scan is important for detection of twins, and this time is the most successful period for the removal of twins. If the mare is scanned empty it is worth re-checking her at 19-20 days as sperm can fertilise oocytes up to 7 days after insemination. 
  • The second scan is 28-32 days after ovulation, this is to check for a positive heartbeat scan, and again that a twin is not present. 
  • A third scan is recommended 45-60days,
    • It may be possible to determine the foals sex at 60 days. 

Rectal palpation

  • Rectal palpation can be performed  from mid pregnancy onwards when ultrasound is unreliable at this stage. 
  • The uterus can be palpated to check its size, position and tone. The foal can also be palpated from mid pregnancy onwards.
  • This cannot always differentiate between single or twin pregnancy, only if the mare is pregnant. 

Blood tests

  • Endometrial cup development begins around 35 days, and blood tests can be performed to test for eCG from 45 – 90 days. This test is 90% accurate, occasional false positives can occur because eCG can continue to be produced if the foetus dies. 
  • Oestrone sulphate is produced by the foetus. Serum levels from mares can be tested from 120 days, levels fall a couple of weeks prior to foaling, this is the most frequent test used for pregnancy testing mares.  

There are lots of ways to find out if your mare is expecting. The dates for when the mare conceived are very important to enable the whole team to pick up on any issues before they become serious.