An abortion is when the foetus dies and is expelled before 10 months of pregnancy. The foal is stillborn if it survives to 10 months but is dead at birth.
What to do if your mare aborts;
- Call the practice to arrange for the mare to be checked and samples of the foetus to be taken.
- Isolate aborting mare immediately and collect aborted foetus and membranes in leak-proof containers. These material must be handled hygienically.
- If the mare has aborted in the field, corner off any contaminated ground.
- Stop movement off the stud/yard pending diagnosis of the cause of the abortion. Do not allow any pregnant mare onto the stud until EHV-1 has been excluded.
- Disinfect and destroy contaminated bedding, and clean and disinfect premises, equipment and vehicles used for horse transport.
Signs of impending abortion;
- Unexpected enlargement of the udder, dripping or running milk. Especially before 320 days of pregnancy.
- Vaginal discharge; mucous staining in tail.
- Coming into season.
Infectious causes of abortion
Equine Herpesviruses 1 and 4 (EHV-1 & EHV-4)
A majority of mares will be dormantly infected with EHV. The infection is likely to re-awaken at times of stress. Abortions caused by EHV happen quickly and can spread rapidly through a herd; they are sometimes known as “abortion storms”.
Steps to prevent and minimise transmission of the disease;
- Vaccinate mares (a course a three injection at the 5th, 7th and 9th month of pregnancy).
- Minimise stress in late pregnancy. Try not to move mares during last month of pregnancy.
- Minimise contact between mares in late pregnancy and avoid new introduction – especially younger horses (eg filly out of training).
Equine Viral Arteritis
This is a notifiable disease but is seen more commonly in continental Europe. Transmission can occur at teasing mating, insemination and contact with aborted material. Along with abortion, the mare may show conjunctivitis, neurological signs and peripheral oedema (eg swelling of lower limbs).
Although there is a vaccine available it is usually reserved for stallions. It is recommended that mares are regularly screened for EVA each year; this is done with a blood test. Stallions and semen should also be declared EVA free before use.
Bacterial and Fungal Infections
This can occur at any point from 3 months of pregnancy. They can be treated, so please call the vet if there are signs of vaginal discharge, matting of the tail or rubbing/itching of the behind. However, prognosis can be guarded in these cases.
Non-infectious causes of abortion
Non-infectious causes are the most common reasons for mares aborting. Some of which are, unfortunately, unpreventable.
Congenital and developmental abnormalities
Umbilical cord abnormalities account for approximately a third of all abortion within the UK. Excessively long or twisted cords can result in a lack of blood supply to the foetus, resulting in the death of the foal and subsequent abortion.
The conception of twins present a problem for mares as they do not have the uterine capacity to support the normal development of more than one healthy foetus. If twins become established one or both are likely to die in the uterus resulting, usually, in an abortion or premature foaling. Not only is the pregnancy wasted, the health of the mare may also be compromised.
Natural reduction has a limited efficiency at reducing twin pregnancies, therefore it is very important to recognise twins at the earliest stage possible and carry out effective treatment to achieve a healthy singleton pregnancy.
Best way to ensure a singleton pregnancy is to scan the mare between 14 to 18 days after ovulation. This is before the embryo has time to be fixed within the uterus. One of the pregnancies can be manipulated and crushed, leaving only one pregnancy. It is possible to reduce a twin pregnancy after this stage but they are generally more difficult and carrier a greater risk of losing the remaining pregnancy.