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Placentitis can be a devastating problem in mares leading to abortion, stillbirths or weak & premature foals.

It is the single most prevalent cause of premature delivery of foals and accounts for nearly one third of late term abortions and foal deaths in the first day of life.

Placentitis is an infection/inflammation of the placenta, the temporary organ that forms to support the foal while it is in the mare during pregnancy.

A variety of causes for placentitis exist, but by far the most common cause is a bacterial infection of the uterus that enters via the vagina and breaches the cervical barrier.

There is also a risk of infection entering the placenta via the mares blood stream. As many of us horse owners know, hairy caterpillars are strongly linked to abortion in mares. The hairs of the caterpillars get ingested or inhaled by the mare. The barbed hairs, covered in bacteria, are then able to travel through the mare and may lodge in the placenta where they cause infection and inflammation.

Mares suffering from placentitis may show a range of signs including a cloudy white to yellow or brown discharge from the vulva and milk dripping or running from the teats. Mares that show these external signs already have significant damage to the placenta and to the foal they are carrying.

Be aware that some mares with placentitis have no noticeable symptoms at all.

Also keep in mind your risk factors:

  • mare has had placentitis previously
  • known area for hairy caterpillars (tent caterpillars, processionary caterpillars, etc – depending on your location)
  • another mare on the property showing signs of placentitis

Recent studies suggest that the inflammatory process involved with the infection releases prostaglandins that stimulate the contraction of the uterus – resulting in abortion of mid/late term foal or premature delivery.

Mares suspected or at high risk of placentitis should be examined and monitored by a qualified veterinarian. Mares with placentitis can be treated with appropriate antibiotics, anti-inflammatory’s and progestagens to help maintain the pregnancy.The key is to catch it as early as possible. The earlier intervention is started the better the outcome for everyone.

Untreated, the foal is usually born premature, under-developed, and often septic. Some mares suffering from placentitis show no external signs and simply deliver a premature or a stillborn foal.

Recognising placentitis AFTER the foal is born is also very important and can improve survival rates for the foal.

We will discuss placenta assessment in another article.

Healthy placenta.

Photo from http://loriequinesection.blogspot.com/

Infected placenta.

Photo courtesy of Becky Hendrix NZ 2019.

Information from:

McKinnon, Angus O., et al. Equine Reproduction. 2nd ed., Wiley-Blackwell, 2011.

image of mare - used for placentitis description

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