Judy Cawdell-Smith & Julianne Farrell The University of Queensland
There are many causes of abortion in mares , and these can be categorised into infectious and non-infectious . Non-infectious causes of abortion include : twinning , twisted umbilical cord resulting in loss of blood flow to the foetus , foetal abnormalities and maternal abnormalities such as other diseases of the mare . Infectious agents ( bacteria , viruses , fungi and protozoa ) can gain access to the uterus via the blood stream as in viral abortion caused by Equine Herpes Virus ; via the vagina and cervix , known as ascending placentitis but in many cases the route of infection is unknown .
More recently , a form of abortion known as equine amnionitis and foetal loss ( EAFL ) has been identified in Australia . Bacteria that are not usually associated with disease in the horse , but are present in their gut and in the environment , are isolated in confirmed cases of EAFL . The identification of setae ( microscopic hair like structures Fig . 1 , Fig . 2 ) of the Processionary caterpillar in uterine and placental tissues suggests that these bacteria are carried from the gut into the uterus and placenta by the setae , resulting in infection of the foetus .
It is important to recognise that when a mare aborts it is not necessarily as a result of exposure to Processionary caterpillars . Unless there is an obvious cause of the abortion e . g . twins , then the diagnosis of the cause of abortion requires a full autopsy , not only of the foetus but also the placenta ( both the white sac as well as the red sac ). If your mare aborts you should collect the foetus and the placenta , place them in a garbage bag and then into a garbage bin and keep as cool as possible ( preferably refrigerated – not frozen ) until you are able to talk to your veterinarian . Remember that viral abortion is easily spread to other mares so biosecurity measures should be put in place to ensure that your other pregnant mares are not exposed to the aborted material as well as the mare which has aborted . Information on what to do if your mare aborts can be accessed at https :// www . daf . qld . gov . au / animal-industries / animal-healthand-diseases / a-z-list / equineherpesvirus / abortion .
Current knowledge about EAFL . Caterpillars have been recognised as a cause of abortion in mares since the outbreak of two conditions : Mare Reproductive Loss Syndrome ( MRLS ) in Kentucky , USA in 2001- 2002 and Equine Amnionitis and Foetal Loss in Australia in 2004 . The caterpillars that have been identified as the agents that cause these types of abortions are the Eastern Tent Caterpillar ( Malacosoma americanum ), associated with MRLS and the Processionary caterpillar ( Ochrogaster lunifer ) ( Fig . 3 ) with EAFL . The Eastern tent caterpillars do not occur in Australia .
The name Equine Amnionitis and Foetal Loss reflects one of the unusual findings associated with this type of abortion ; ‘ amnionitis ’ refers to inflammation of the amnion ( the white sac surrounding the foetus ). The umbilical cord is also often affected and bacteria are commonly isolated from the amnion , umbilical cord and foetus . There are a diverse range of outcomes to this condition : acute abortion in which little change to the parts of the placenta is seen and diagnosis is based on laboratory findings ; chronic cases where there
Figure 1 . Scanning electron microscope image of a seta from O . lunifer . Note the scale the seta is about 0.1 mm in length Image : Bronwen Cribb .
Figure 2 . Electron microscopy of mirrors on a Processionary caterpillar , Ochrogaster lunifer , a ) bundles of setae held within 2 mirrors ; b ) enlarged image of the setae bundled together Image : Bronwen Cribb
Page 18 • The Australian Quarter Horse Magazine • July • August • 2017