Widespread cases of cattle deaths in north-east Victoria

Several deaths of lactating cows have been reported to veterinarians throughout Seymour, Ruffy, Euroa and Mansfield, as the regions endure cold, wet and windy weather conditions.

Seymour Central Veterinary Clinic veterinarian Freya Worne said a "perfect storm" for lactating cows experiencing inclement weather and minimal access to clover, had led to cases of hypomagnesemia.

Dr Worne said one client had reported death in a cow with an autumn-drop calf at foot earlier this month, followed by a lethargic and weak appearing cow last week.

"It was confirmed hypomagnesemia on blood (test) and that's what she had and that is what killed her," Dr Worne said.

"The remainder of this herd has been offered a loose lick containing a high level of Mg and calcium, which they have aggressively been attacking, as well as increased hay supplements and lick blocks.

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"Before this outbreak, this mob of cattle had been moved to a paddock with predominantly ryegrass and the farmer had been supplementing with hay throughout this period, however, we suspect that poor weather last week combined with the move to a new paddock had reduced the feed intake sufficiently in some individuals to cause a significant drop in Mg levels."

A cow in peak lactation needed a constant source of Mg to replace the large amount lost from the body in milk, she said.

Grass tetany occurred when Mg losses in milk exceeded the amount consumed in the pasture, with the highest risk period occurring from calving through to the first few months of lactation.

"Weather and feed conditions have been conducive to increase cases," Dr Worne said.

"Mg levels in the animal rely almost entirely on dietary intake of Mg, unlike calcium that can be sourced from large stores within their bones.

"Anything that causes a reduction in feed intake will put cows at risk of low Mg, including transport, yarding and movement to a new paddock or an unfamiliar feed type and cold wet windy weather."

Farmers reported nervous signs, aggressive cattle behaviour and ultimately death.

"The acute and the per-acute forms present and progress to death incredibly fast," Dr Worne said.

"Sometimes a cow can show classic tetany signs, staggering, seizures, grinding teeth, hyposalivation and frothing at the mouth.

"If farmers are finding unexpectedly dead stock, especially signs of struggle on the ground, and they're unsure if Mg is involved, there are some really simple lab tests we can do on animals up to 24 hours after they've died."

However, she said there had also been reports of more chronic and slower forms, with cattle appearing dull and lethargic but hypersensitive to sound, light, and aggressive.

"If you can safely approach the animal - bearing in mind seizures or tetany animals can be extremely agitated and dangerous to approach - one of the liquid products containing Mg and calcium should be injected under the skin," she said.

"If the animal is down or affected, this may need to be injected intravenously.

"This is best achieved by a vet due to the risk of excess treatment and the dangers of excess calcium and Mg."

But Dr Worne said prevention was best and urged supplementary feeding of recently calved cows if cold, wet and windy conditions continued and if animals or paddocks were at high risks.

Providing Mg supplementation in the form of loose lick or lick block is recommended in periods or paddocks of high risk.

"When the supplement is provided it is recommended two to three weeks pre-calving to allow the gut to adapt and ensure optimum Mg uptake in the post-calving period when demand is highest," she said.

Agriculture Victoria livestock extension officer Alison Desmond said grass tetany was most common during winter, with peaks during times of cold, wet and windy weather conditions.

"Older cows, which are pre calving or lactating and are overly fat or very thin are most susceptible to this metabolic disease," Ms Desmond said.

Lush rapid growing pastures and grazing cereal crops are generally high risk due to low Mg and calcium levels, and also pastures excessively high in potassium can inhibit the uptake of Mg by cows.

"Grass tetany usually occurs when cattle graze these types of pastures after calving through to the first few months of lactation," Ms Desmond said.

"Cows in overly fat condition, combined with a period of windy, cold and wet conditions, things can go wrong.

"Lactating cows are most at risk, as they lose magnesium in milk, and they need a constant source of Mg to replace the large amount lost from the body in milk. When cows are using a lot of magnesium but not bringing it back into the system is when grass tetany rears its head."

She said early treatment was critical to recovery and the chance of saving the animal.

"If you can get it early enough, they will be standing on their own, jittery, they can fall over easily because it affects their nervous system so they're very sensitive to sound and movements," Ms Desmond said.

"If you find them and can get them in a paddock or yard, or they are down and still alive, you can give them a 4 in 1 mineral solution pouch (Mg and calcium solution) ."

She said good management was essential to prevent and manage grass tetany.

"With ongoing overcast, wet and cold weather, I'd suggest a good idea is increasing the MG intake of at risk mobs of cows," she said.

"This includes feeding hay and providing lick blocks - it is a small price to pay with cattle worth a lot of money at the moment. It's a small investment to prevent a big problem.

"Producers need to be forward-thinking and identify their trigger points."