Equine Abortion

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.

Twin pregnancy

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.

Equine Herpes Virus

Equine Herpes Virus (EHV) is an incredibly infectious virus and is much more common than many horse owners believe.
There are several forms of the disease, however the most serious are EHV 1, 3 and 4.

Type 3 is a sexually transmitted disease which is rare in the UK.

Types 1 and 4 are common and cause respiratory disease, neurological signs and abortion in pregnant mares. The respiratory form circulates continually in the equine population and your horse may become infected and show very few, if any, signs and then become a carrier. Occasionally a much more serious respiratory form is noted where horses have very high temperatures, glandular swelling and a clear nasal discharge.

They generally feel very unwell and will stop eating.
Treatment includes supportive care and occasionally anti-viral drugs.

Rarely a neurological form is seen where horses become wobbly on their back legs, have difficulty urinating and eventually may be unable to stand. Some horses may not recover from this form of the disease.

Mares may abort up to 12 weeks after exposure to EHV type 1 (which may be from a carrier or a horse not showing signs of illness) The abortion is usually sudden and generally in mid to late pregnancy.

A vaccine is available for this disease (EHV types 1 and 4) which should be used alongside good disease prevention measures. It reduces the spread of the disease and gives protection against respiratory disease caused by EHV, it also reduces the chance of abortion occurring due to EHV Infection.

Vaccination involves two initial doses 4-6weeks apart followed by 6 monthly boosters.

Pregnant mares are vaccinated at 5, 7 and 9 months of pregnancy. We strongly recommend vaccination of all pregnant mares and horses which are competing or mixing with other horses regularly.