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EHV Shortage - ADVICE

The New Zealand Thoroughbred Breeders' Association (NZTBA) has initiated the following advice for all broodmares owners.

Suggested management of non-vaccinated mares against EHV

As mare owners you will now be aware of the shortage of EHV (Equine Herpes Virus) Pneumabort K or Pneumequine vaccines and many mares are now unvaccinated. The NZTBA thought it was timely to send some reminders and advice on Herpesvirus. As with any animal health issue, we always suggest you discuss your particular situation with your Veterinary surgeon, however guidelines are as follows:

  •  STRESS is a major contributor to the spread of ANY virus and with the forthcoming Broodmare sales, foals being weaned, the mixing of mobs and some stock being wintered off farm into new environments, it is essential to minimise the stress associated with these events.
  •  It is not just broodmares that carry the EHV virus therefore; prudent management of ANY particularly new horses/ponies on your farm is always wise even with vaccinated mares.
  •  The virus replicates and is shed from horses' upper respiratory system and is commonly spread by exhaled droplets in the air. Once infected, most horses harbour the virus in their lymph nodes for life.
Some reminders and advice regarding Herpesvirus:

  •  Management of pregnant mares is of primary importance for control of abortion caused by EHV-1.
  •  Carrier horses show no external signs of disease when the virus is inactive, or latent. They are capable of shedding virus, with or without clinical disease, particularly at times of stress, for the rest of their lives.
  •  Primary indications for use of equine herpesvirus vaccines include prevention of EHV-1 induced abortion in pregnant mares, and reduction of signs and spread of respiratory tract disease (rhino pneumonitis) in foals, weanlings, yearlings, young performance and show horses that are at high risk for exposure. Many horses do produce post-vicinal antibodies against EHV, but the presence of those antibodies does not ensure complete protection. Consistent vaccination appears to reduce the frequency and severity of disease and limit
    the occurrence of abortion storms but unambiguously compelling evidence (that vaccination will prevent all signs of disease) is lacking. (American Association of Equine Practitioners)
  • This means even horses that are up to date with their EHV 1 vaccination programme may still be at some risk, so good management, infection control, and quarantine approaches are essential to lowering this risk of infection on your stud.
Guidelines in the case of Abortion:

  •  Cases of abortion triggered by the disease usually occur without warning, typically late in pregnancy – after seven months. Occasionally, abortion can be triggered as early as four months. EHV abortion can occur from two weeks to several months following infection.
  • If you come across an aborted foetus immediately remove other paddock mates to another paddock but do not mix them with new horses. Treat the mare, foetus and placenta as highly contagious and ring your veterinary surgeon. Practise STRICT personal hygiene protocols including farm vehicles, dogs and gear. Dispose of all aborted product judiciously, eg. by burning or deep burial after your vet has completed his investigation.
  •  Mares infected with herpes virus very late in gestation may give birth to live but very weak foals which are highly contagious so undertake thorough disinfection after handling all new born foals especially if they are weak or sick.
  •  Rigid quarantining of the sick animal until the risk of transmitting the infection has passed. Separation of any horse that has aborted or shown signs of fever, respiratory disease, or neurologic disease from healthy horses. Ideally, sick horses should be moved into a separate building. If they are to be left in the paddock ensure they do not share water troughs and that they remain at least 15 metres away from other horses.
  •  Do not share equipment among horses on the property, given that the virus can be spread through contaminated objects such as water and feed buckets, even bridles.
  •  It is important that people in contact with the horses use proper biosecurity measures. They should wash their hands after handling one horse and before handling another. They should also change their clothes and footwear after working with a sick horse.
  •  It is essential that our industry grows its understanding of the effect of EHV 1 virus in New Zealand, so for all abortions work with your local equine veterinarian to establish a diagnosis and ensure you are minimising the risk of disease spread.
Owners should take extra precautions in the absence of adequate vaccination cover:

These include:

  •  Group maiden mares separate from multiparous mares
  •  Isolate all newly arrived mares from resident mares
  • Aim to run mares in as small a group as possible and avoid mixing.
  • Ideally, a person caring for a sick horse should not work with healthy horses. When this is not practical, healthy horses should be handled first and sick horses last.
  • Wearing gloves and using disinfectant to sanitize footwear can also help minimize the risk of people spreading the virus between animals.
More points to note:

  • All forms of herpes viral disease have now been documented in New Zealand and outbreaks are likely to occur annually.
  • Stress of transportation and new environments are one of the most likely triggers for reactivation of the latent form.
  • A period of isolation post arrival on farm is advisable. The duration of this is debatable but not less than 10 days would seem prudent.
Prudent management can help to reduce the risk to your mares and unborn foals. At this stage there is NO set date for the release of more vaccines, but hopefully this will be before foaling, as the risk increases significantly in the foaling paddocks.