Warning issued after horses die from eating toxic plant

A TOOWOOMBA equine veterinarian has issued a warning for people to check their paddocks after two horses died from eating a toxic weed this week.

Equine Veterinary Services Toowoomba Practice Manager Carol Smith, 60, said the two horses were on the same Darling Downs property and had been spotted by the owner eating Malva parviflora, also known as marsh mellow.

Dr Smith, based in Hodgson Vale, outside of Toowoomba, said symptoms of poisoning from the toxic weed mimicked symptoms presented by the Hendra virus and came on rapidly.

The two horses, who Dr Smith declined to share more information about due to client confidentiality, had to be euthanized only 36 hours after the symptoms appeared.

"Clinical signs can develop quite rapidly and include weakness, muscle tremor, recumbency, heart failure and death," a warning post on the equine vet's Facebook page said.

"As many of these signs also resemble Hendra virus, any unvaccinated horses are unlikely to be hospitalised for intensive support, without first performing a Hendra exclusion test, a potentially fatal delay."

Equine Veterinary Services Toowoomba have issued a warning for horse owners to be aware of a deadly weed. Picture: Equine Veterinary Services/Facebook
Equine Veterinary Services Toowoomba have issued a warning for horse owners to be aware of a deadly weed. Picture: Equine Veterinary Services/Facebook

Other signs also included a horse appearing weak, struggling to breathe, hanging its head, and repeatedly lying down and getting up before staying down.

Dr Smith said an effected horse could die or have to be euthanized within two days of eating the marsh mellow plant as there was no antidote for severe cases of toxicity.

"There is anecdotal evidence of a couple of horses surviving, but it's often severe," she said.

"We can give them supportive treatment and fluid but there's no antitoxin for this toxin."

The treating vet had to approach the now deceased horses as if they had the deadly Hendra virus, she said.

"You can't differentiate whether it is or not, so you have to initially treat it as if it is Hendra virus by taking all the precautions."

"If it's Hendra virus the property is quarantined until it is ruled out.

"So you have to do an exclusion test on these horses."

Equine hospitals do not accept horses exhibiting clinical Hendra-virus like symptoms, until the special exclusion test results have been returned.

By the time negative exclusion tests came back for the two horses this week, it was too late.

The Hendra-virus can be fatal to both animals and humans.

Dr Smith said drought conditions were the likely cause of the marsh mellow outbreak.

"We've had prolonged drought and then we had rain in late autumn, which brought on a flush of weeds in the bare paddocks," she said.

"Now you've got owners thinking they have a bit of green in the paddock, but it's mostly weed.

"That's why we've put out a warning as it's not a problem that happens every year."

Equine Veterinary Services Toowoomba have issued a warning for horse owners to be aware of a deadly weed. Picture: Equine Veterinary Services/Facebook
Equine Veterinary Services Toowoomba have issued a warning for horse owners to be aware of a deadly weed. Picture: Equine Veterinary Services/Facebook

Dr Smith said horses would not generally eat the weed if they had enough other food and grass.

"Horses can eat a small amount of weed and be OK if they're still eating a good diet," she said.

"But when there's a situation where there's no other grazing, they'll eat large volumes of weeds.

"It's a fairly rare condition but if you get the right set of circumstances it can be bad."

She said the drought had also increased the price of hay, contributing to farmers struggling to feed their horses.

Livestock owners are now being encouraged to remove any of the marsh mellow weed from their paddocks.

Dr Smith said horses should be fed good quality hay, cubes and have access to good pasture.

"If owners notice the weed they should remove the horse from that paddock and try to remove the weed as it will help reduce a reinfestation the following year," she said.

Sheep and cattle were also susceptible to getting sick from the weed if large amounts were consumed, though cattle were the least susceptible.

Katherine Jones posted under the vet's Facebook warning post that her pony died after eating marsh mellow.

"My mini pony ate it and it killed him worse death he was so ill and now it's nowhere near my paddocks (sic)," she wrote.

Lesley Mcdowell and Amy Brooks both posted under the vet's Facebook warning post that they had goats fall ill and recover after treatment or sheep died after eating the same weed.