Foetus to Foal

This article is from the August 2019 Horse Deals magazine.

Dr Elizabeth Barter BVsc (Hons) graduated from the University of Sydney in 2012 and commenced her first veterinary role in a mixed practice at Macleay Valley Veterinary Services and Macleay Valley Equine Reproductive Services. To further her interest in equine reproduction, Liz moved to Newmarket in the UK working at Rossdales as a stud assistant, then later at Twemlows Stud in Shropshire. Liz joined Scone Equine Group in 2017 where she continues her interest in equine reproduction and medicine and is now a permanent part of the ambulatory team at Scone Equine Hospital.

Following the successful breeding of the mare, the real miracle starts to take place. With advances in reproductive knowledge and ultrasound, the foal can be assessed from a very early stage and at many times successful interventions can occur to ensure a happy and healthy foal is born. If you are concerned about your foal or mare at any stage during pregnancy contact your equine veterinarian.

Day 6 - Embryo Flushed
Equine embryos can be flushed from the uterus from day 6. The embryo at this stage is approximately pin head size, just visible to the naked eye.

Day 12 - Embryo Vesicle Visible (early scan)
The embryo vesicle can be seen from day 12, however, routine examination is normally delayed to day 15 post-ovulation to confirm pregnancy. At this stage, the vesicle moves around the uterus sending signals to the mare, so she recognises she is pregnant.

Day 17 - Twin Embryos
The embryo stops moving around the uterus and implants at approximately day 17. It is important for mares at risk of twin embryos to be examined by an experienced veterinarian with ultrasound before day 17 to detect twins.

Day 21 - Heart Beat Scan (mid scan)
A heartbeat can be seen from day 21. Unfortunately, some pregnancies are lost between the early scan at day 15 and the heartbeat scan. The mid scan helps assess for a healthy embryo and allows mares to be rebred if there are problems.

Day 45 – Foetal Scan (late scan)
A foetal scan at approximately 45 days allows mare owners to prepare for the management of a pregnant mare such as vaccination schedules. There is little harm to mare and foal from repeat ultrasound examinations. The sex of the foetus can be determined by experienced veterinarians from day 59 to 68. The day of foetal sexing is dependent on veterinarian preference.

Mid Gestation – Late Sexing Opportunity
From day 90 – 120 it is possible for an abdominal ultrasound to be performed to identify the sex of the foal. To perform this requires patience and experience as the foal moves around the uterus. It is important to keep pregnant mares happy and active in this early stage. Mares can remain in high-level training up to 120 days as the foetus is smaller than a rabbit. From 120 days onwards exercise can be slowly decreased as the foal continues to grow.

Day 250 - Last Trimester
In the last three months of gestation, the foal grows enormously from 5kgs to 50kgs. This places large demands on the nutrition of the mare and it is important to increase the mare’s feed as she is now eating for two. The foal at this stage is no longer within the pelvic canal and can be difficult to image. Rectal ultrasound can identify the placenta and assess for placentitis (inflammation of the foetal membranes). Placentitis can be caused by many different reasons and is a common cause of sick foals and later-term abortion.

Foal at Term
The gestation of a mare can vary from 300 to 400 days with an average of 340 days. At birth, the foal is required to undergo a change in position to turn themselves around into the correct position. Once mares go into labour the foal should be on the ground within 20 minutes. If you are concerned your mare is having trouble foaling, please contact your equine veterinarian urgently for advice.

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