Equine owners have been urged to be vigilant, as an invasion of subtropical grasses lead to an 'unprecedented' number of horses getting big head across South East Queensland.
Hyperparathyroidism, commonly known as 'Big Head', is a calcium deficiency disease induced by a diet with a persistent lack in calcium, excess in phosphorus or imbalanced calcium to phosphorus ratio.
Horses cannot access grasses such as Setaria, buffle, Kikuyu, and Signal grass due to the high level of oxalates, and long term grazing can result in a severe calcium deficiency.
The disease can have severe and debilitating effects on horses including difficulty breathing, painful movement, lameness, enlarged facial bones and may even cause death.
Logan equine dentist and veterinary nurse Anna Minogue services horses across south east Queensland.
Ms Minogue is warning horse owners to be vigilant, after seeing an unprecedented number of horses with bighead this year, many in quite serious trouble.
"I'm based in Logan, and I'm seeing a lot of big head cases around my area and I'm also seeing it a lot on the coast, which is not like abnormal," she said.
"I've been called out to see dozens of horses who 'have trouble eating', with owners believing they need a dental.
"On arrival, I discover the entire skull is so swollen the horse cannot close its mouth. Teeth can also become loose.
"They will often drop feed or not be able to graze at all. Unfortunately without very swift action, these horses can starve to death."
Anna said a significant rainfall in recent months, has caused subtropical pastures like Setaria to spread like wildfire across the region.
"We've had such a very wet summer, it's made the setaria go bonkers," she said.
"My property's never had Setaria, and this year it does. I think it's just growing more. It's always something that I've seen, but horses don't have any idea about it."
One area suffering from the spread of the invasive plant is the Lockyer Valley, with some parts of the region receiving close to 500mm of rain since the beginning of November.
Setaria may contain anywhere between 30 and 80 grams of oxalate per kg of (90pc dry matter) pasture, which translates to a huge amount of calcium being needed to balance the calcium to oxalate ratio to prevent bighead.
Ms Minogue said horse owners can avoid big head by moving their horses out of high oxalate pastures and supplementing the adequate nutrition.
"The issue that I'm finding is that a lot of big head affected horses are stiff, they're not right in the gaits.
"It doesn't present as big head until they're like 30 per cent calcium depleted, so there's a huge process that goes on before the actual swelling of the head happens.
"If you have a horse in southeast Queensland, just give them supplement, or just make sure you're giving Lucerne and low oxalate hay such as Rhodes. Avoid high oxalate feed such as bran and pollard.
"I've used Jenquine Bone Formula Forte and had success with it and I've had clients that have had success with it as well. A tropical grass blend works as well."
Full recovery time for horses may take three months, with improvement seen as little as two weeks, however, Ms Minogue warned some horses will never improve if they are not treated early.
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