Three ultrasound examinations are advised:
The first ultrasound examination should take place at 14-15 days after insemination (or the last date of covering). At this stage the embryonic vesicle is not fixed in the uterus and is mobile. It is an ideal time for identification of twin pregnancies
The second ultrasound examination should take place at approximately 21 days. The conceptus will have implanted at day 17, and will usually be found in the base of one of the uterine horns. The embryo proper can usually be identified at this stage. This scan checks that the conceptus has implanted properly into the uterus and that the embryo is developing.
Finally a third ultrasound examination is recommended before day 34 of pregnancy. This scan is often referred to as the ‘heartbeat’ scan as after approximately day 24 the heartbeat of the embryo can be seen on the ultrasound scan. After day 35 endometrial ‘cups’ are formed and if the mare loses the pregnancy after this time, it is unlikely that she will come back into oestrus during the same breeding season.
Further or additional scans may be advised if twins are identified and one conceptus manually reduced, to check that only one pregnancy remains.
If only one pregnancy scan is to be carried out then a scan between 21 and 34 days of pregnancy is advised, although if twins are identified at this stage it is much more difficult to treat and much more likely to result in the loss of both embryos if this is attempted.
Later scans can be carried out but after day 90 the pregnancy begins to drop down in the abdomen and transrectal ultrasound is much less useful
Manual Pregnancy Diagnosis
In later pregnancy (four to five months onwards) it is possible to diagnose pregnancy by manual rectal palpation. This cannot identify twins.
In later pregnancy we can monitor the developing foal and placenta by trans-abdominal ultrasound examination. This can allow identification of problems in late pregnancy such as infection (placentitis).
Once the pregnancy is established then it is possible to take blood from the mare to see if she is pregnant. There are two main hormones that are measured depending on the stage of pregnancy:-
Oestrone sulphate – this detects pregnancy from around 110 days to close to term. It is produced by the developing foal so a positive result indicates a live foal.
PMSG – can detect pregnancy from around day 45 – day 90. This is produced by the mare from the endometrial ‘cups’. If the mare loses the pregnancy then this hormone will remain high for some time, therefore it does not necessarily identify a live foal.
There is a time gap between day 90-120 when none of the blood tests are very accurate and false negatives may occur if mares are blood sampled in this window.