Matt Boon from Prime Livestock Veterinary Services is a vet based in Mansfield who specialises in livestock. Mr Boon saw his first case of the disorder last week.
“There is always someone new to cattle, particularly post-Covid, there is a lot of people moving to country areas who may not be aware of it,” Mr Boon said.
“We’re going to start seeing more of it through winter and early spring.”
Grass tetany, also known as hypomagnesemia or grass staggers, is a metabolic disorder that affects grazing livestock, including cattle. It occurs when there is a deficiency of magnesium in the diet, leading to low levels of magnesium in the spinal fluid.
“Because of the seasonal conditions there is not a lot of magnesium in the grass — rapid growth dilutes the magnesium,” Mr Boon said.
Green, lush grass is high in protein and energy, making it an appealing option for cows, but the dry and stalky grass characteristic of summer is much higher in magnesium and calcium.
“Temperature comes into it, frost is damaging to most grasses, so the grass protects itself by pulling its nutrients down out of the leaves and into the root systems, which means there is even less in the edible portion as its draws the minerals down into the roots,” Mr Boon said.
“When there’s frost overnight followed by a day of clear skies, good weather, there isn’t time for the plants to put the nutrients back in the leaves for photosynthesis, so the cows start grazing the grass before the nutrients are back in it.
“So, it’s that specific order of bad weather, good weather, bad weather, which we see at this time of year, that is the specific risk for low magnesium.”
Although preventable, grass tetany progresses fast — with serious consequences.
“Unless you get on top of it really quickly you can end up with calves that no longer have a mum,” Mr Boon said.
Symptoms include muscle twitching, staggering gait, weakness, progressing to an inability to stand, sudden onset nervousness and excitement and most commonly, aggression.
Although there is not one specific breed more prone to tetany, identifying high-risk animals makes the potentially fatal illness easier to prevent, Mr Boon said.
Grass tetany is particularly common in calves and lactating cows at this time of year, as well as older or fat cows.
“Autumn calving cows or cows that are lactating are putting resources into their milk and losing more nutrients,” Mr Boon said.
“Once cows hit third or fourth calf, at around six or seven years old, the internal systems that help to control the balance of minerals become sluggish.
“So older animals aren’t as equipped to pull minerals from other areas of the body to manage that imbalance.”
Often, considering the make-up of the paddocks themselves is one of the best forms of prevention.
“Grasses-dominant paddocks have the lowest magnesium, and will have less magnesium than say a clover-dominant paddock,” Mr Boon said.
“In a pasture-based beef system, everything that they are being fed is from the paddock, whereas in the dairy system they will be fed while they are being milked.”
Mr Boon recommends feeding out hay that has a higher magnesium content and spraying with a mix of causemag (Magnesium sulphate), molasses and water, feeding the causemag at a rate of 50 grams per head per day.
Finally, Mr Boon warns that grass tetany is a herd problem. There needs to be focus on the entire mob if a single animal becomes affected, he said.
For assistance or advice on managing and preventing outbreaks, contact Prime Livestock Vets on 0447 496 428.
