Plants that poison horses

There are a number of native plants that can poison horses in remote areas. Horses born and bred in the area are less likely to have problems with poisonous plants than animals that are new, presumably because old hands are more likely to know what to steer clear of (those that scoffed into it didn’t live to breed on). There can be an increased chance of deaths during a drought when stock eat plants they’d normally avoid, but the risk is highest when the drought breaks and a particular poisonous plant flourishes. Parts of the Kimberleys have a lot of trouble with horse poisoning and it has always been particularly difficult to prevent deaths in the Alice Springs region. This is perhaps the main reason why motorbikes replaced horses much earlier in the Alice Springs area — something that sped up during a run of good seasons in the late 1970s, when indigofera plants flourished.

Pyrrolizidine alkaloids are found in Heliotrope and native ‘rattlepod’ (Crotalaria) plants as well as in introduced Paterson’s Curse/Salvation Jane. Too high a consumption results in liver damage and death, and there is no cure. Common names for the illness are ‘Kimberley disease’, ‘walkabout disease’ and ‘Chillagoe disease’.

Birdsville Indigo (Indigofera Linnaei) is a hardy native plant that is found across northern Australia but it is most common south of Tennant Creek. The indospicine contained in Birdsville Indigo is toxic to horses but not to cattle, and horses that consume quantities will develop the eventually fatal Birdsville disease. Birdsville Indigo plants contain the indospicine toxin all year round but poisoning is most common after Spring and Summer rainfall, because Birdsville Indigo responds to rain faster than other plants. A close eye needs to be kept on what is growing in horse paddocks, and feeding protein supplements high in arginine can help prevent the disease.

Swainsona species such as Darling Pea are winter-growing plants that poison horses and cattle due to Swainsonine, an indolizidine alkaloid that is poisonous to livestock. Ingestion causes similar symptoms to Birdsville disease. Swainsona poisoning is typified by loss of co-ordination and hoof dragging, which wears down the front surface of the horses hooves, especially the hind hooves. Apparently if horses and cattle have only been grazing on the poisonous plants for 4 weeks or less, symptoms can be reversed – but if any longer damage is permanent and eventually fatal. Horses become too dangerous to ride as they lose control of their hindquarters, and they die in a matter of weeks if they continue to have access to the poisonous plants. Unfortunately horses and cattle seem to become addicted to Swainsona and Birdsville Indigo plants and will deliberately seek them out once they get a taste for them.

Ironwood and Whitewood trees can also cause poisoning in horses, camels and cattle as well as Georgina gidyea at certain times of the year, when the latter contains a lot of fluoroacetate (1080).

The Horse Federation of South Australia has a useful list of southern plants that can cause problems and there is a detailed discussion by Dr Ross McKenzie about poisonous Australian natives at Australian Plants Online. (It’s enough to make you realise that trying unfamiliar bush tucker would be very unwise.)

Tags: ,