A disease that can kill cattle is worse this year than others, a Northland farmer says.
The disease, called theileria, is caused by a blood-borne parasite that only affects cattle and is usually transmitted by ticks. It causes anaemia and can be deadly.
The disease is widespread across the northern half of the North Island, but in previous years cases have been found on the West Coast of the South Island.
Sheep, beef and dairy farmer Douglas Conn, who farms near Dargaville in Northland, has lost about 15 calves to theileria so far this year.
Mr Conn buys hundreds of calves each year and rears some of them on nurse cows instead of milk powder, and it's these which have died.
He said the disease had been on his farm for about two years.
"And it's getting worse ... normally the theileria comes a bit later but it's come a lot earlier this year.
"[They're] just anaemic, they [calves] can't walk, they're lethargic, the odd one dies - and they are big calves, not little pot bellied runts... they're all white in their eyes and gums, they've got no energy and drink a lot of water."
Anything that gets the disease seems to eventually die, and the problem is also on his neighbour's farms, Mr Conn said.
"Another beef farmer he had 150 breeding cows and he lost 15 calves last year.. there's a local guy selling drenches and products, and when he was going around some of clients, they're giving up running breeding cows."
Mr Conn said he was now thinking about moving away from using nurse cows.
"I just need to revisit the whole exercise, certainly the losses have just been too high.
"A lot of these cows are all bought in as nurse cows ... so maybe there are ticks and a good mix of parasites coming in. If you had a closed environment it wouldn't be so bad."
The number of cases of the disease has steadily increased since a new strain of theileria orientalis called ikeda was first identified in Northland in late 2012, brought in to the country from historically stored serum.
The Dargaville Veterinary Centre is used to dealing with the disease, and senior veterinarian Donald Thomas said one recent case had killed several calves being reared on their mothers.
"The calves we were seeing were lethargic, slow ... and basically they died shortly after.
"Applying an effective tick treatment may work, but quite often we are too late treating."
Mr Thomas said exposure to ticks could happen from late July before farmers saw them on the animals.
"Do not buy cattle from outside tick areas in New Zealand, that'll be probably somewhere south of Taupō.
"If the cattle come from a tick-free area then don't send them into a tick area, because more than likely they'll come down with theileria."