Abortion caused by Equine herpesvirus 1 (EHV1) has occurred sporadically in horses in Australia for some time. The virus is found and known world-wide. It is a serious and highly contagious disease that all horse breeders should be aware of.

There are five different strains of Herpes virus affecting horses and donkeys in Australia. Only EHV1 can cause abortion. It is also a common respiratory disease in young horses and has been known to cause neurologic disease.

What you should be looking out for

  • Abortions between 7 and 11 months of gestation, occasionally as early as 4 months
  • Abortions occur suddenly, with no prior warning
  • Foetus may be expelled still covered in placenta
  • Mares affected late pregnancy will have weak foals, may be jaundiced, difficulty breathing
  • Early foal death (may only survive for a few days)
  • Mare will seem normal otherwise (they do no exhibit any other signs of disease)

After aborting, the virus may still be shed for up to 2 weeks. The virus may remain infective in the environment, horse particles e.g. hair for up to two weeks in cool and moist conditions if cleaning and disinfection are not adequate.

What if I find an aborted foal?
If there is no cause of abortion that is obvious, it is important to make sure the virus does not spread out further than the property.

  • Isolate the aborted mare- no contact between her and any of the horses on the property
  • Leave her halter and head rope on her
  • Any equipment in her stall or paddock should be left with her as these may contain viral particles too
  • Do not move any horses into her direct environment
  • Call your veterinary surgeon
  • Wear gloves to pick up the foetus and placenta and put it in a strong plastic bag. Keep this package cool for the veterinarian to examine when they come to the property. Do not throw it out as it may contain valuable information and/or specimens that your veterinarian may need.
  • If the pasture has been contaminated with foetal fluids and/or tissue please treat the area (and a large margin around it) with lime and fence it off.
  • Provide quarantined mare with her own feed bin and water container, do not use these for any other horse
  • Keep mare completely isolated until a diagnosis has been made

Disinfection of people that have been contaminated

  • Disinfect hands and boots with a good surface disinfectant e.g. Iovone scrub, Chlorhexidine, etc (your veterinarian will give you details when you call)
  • Shower and change clothing
  • Clothing should be washed with a disinfectant and sun-dried
  • Restrict access to mare, and limit the number of personnel allowed in (maybe designate one person to care for her). This person should disinfect themselves after every time of contact with the mare and her environment.
  • 5% formalin foot bath and a scrub brush should be placed outside her stall for disinfection of boots

What if EHV1 is confirmed on your property?
There is unfortunately no significant treatment for this infection. Most foals will die within a few days if born alive despite any treatment.

Our main concern is limiting transfer of disease to other horses within the property and in neighbouring properties. Isolation of the infected mare will last for at least 30 days, after which she can be treated as a dry mare and breed. Please consult your veterinarian about a vaccination program for EHV1 and EHV4. This does not induce 100% immunity to the viruses, however does reduce the severity of virus shedding, and hence the risk of infecting other horses on your property.

Communication between you and other stud farms is essential. Simple precautions will reduce the spread of disease and minimise disruption of horse movements during the season and hence productivity.

How can I prevent this disease outbreak?
Disease introduction can be minimised by employing good management practices such as the following:

  • Keeping weanlings and yearlings and non-breeding stock on a separate portion of the farm
  • Separate pregnant, non-pregnant mares and mares with foals
  • Isolate visiting mares on the stud for at least 3-4 weeks, and keep them in smaller groups of 2-3
  • Minimise stress factors which can affect immunity
  • Establish proper isolation and quarantine facilities and protocols
  • Train staff in understanding quarantine measures
  • Clean and disinfect floats after every journey
  • Vaccinate mares in 5th, 7th and 9th month of pregnancy

If there are any concerns please call your veterinarian. It is a team effort to ensure that this disease does not impact on the breeding season.


  • There is a vaccine available for use as an aid in the control of EHV-1 abortion when used in conjunction with appropriate management practices.
  • Primary Course: 2 injections after 5 months of age 4-6 weeks apart.
  • Pregnant mares: (that have been previously primed) should be vaccinated during the 5th, 7th and 9th months of pregnancy with a single dose on each occasion. Infected, pregnant mares vaccinated with this product may still abort.