Tick eradication not Theileria silver bullet
Ensuring young stock are sourced from areas caught up in the outbreak of Theileriosis is still the best defence for farmers’ in areas where the disease is prevalent, says Bay Of Islands vet Garth Riddle.
In some cases the ikeda strain, identified in New Zealand for the first time last autumn, has left cows dead while others have resorted to once-a-day milking to ease the stress on affected animals.
In May, after a spate of cases in Northland, MPI, Beef + Lamb, DairyNZ and New Zealand Veterinary Association warned the hot dry autumn may have increased tick populations. Now it seems the warm spring combined with calving stress is causing a spike in cases across Waikato and Bay of Plenty.
DairyNZ put out a warning to producers last week to be alert for symptoms: anaemia, as indicated by pale mucous membranes, exercise intolerance and increased respiratory and heart rates. Affected cows are lethargic, likely lagging behind mobs when moved, if not recumbent.
“There have been a number of cases and a growing number of cases,” DairyNZ’s chief scientist Eric Hillerton told Rural News.
“Ticks transmit the disease and it’s been such a devastating spring in terms of tick numbers,” he added.
Colleague John Bluett, an animal husbandry specialist with DairyNZ and a Waikato dairy farmer, said cases are happening “exponentially” in the Waikato at the moment.
“The weather and long grass have been ideal for the tick that carries it.”
The ticks infect cattle with the Theileria protozoa when they attach to the animal, then the protozoa destroys red blood cells, causing the anaemia and other symptoms. Cattle will develop immunity after exposure to the disease but if stressed before that immunity develops, they can go down with milk fever-like symptoms and even die.
“If you think you’ve got it, get the vet in straight away and get a test done,” urges Bluett, who had a cow go down with the disease on his farm last week.
“These cows have to be nursed very gently. Give them plenty of high energy feed because they’ve not got the energy to go and get their own, and it will take them a while to recover.
“Some farms that have had quite a few cases have put them on once-a-day milking.”
Hillerton says keeping an eye-out for ticks around the tail head, base of udder and inside the legs – “basically wherever the tick can get close to the skin” – is a good idea, but warns the ticks are hard to spot as the immature forms are only the size of a pinhead, and even the adult is only 2.5mm across initially.
“It grows to about the size of a pea before they drop off.”
Cattle movements, and possibly other animals including birds, spread the ticks.
“They’ll go on virtually anything warm blooded and are well recognised on deer,” says Hillerton.
Other strains of Theileria have been present in New Zealand for at least 30 years. There is no animal-to-animal risk of spread in the absence of ticks, nor is there a human health or food safety risk associated with the disease.
