Animal health experts are mystified by anaemic calves dying in Northland with suspected infection by theileria, a protozoan cattle parasite spread by ticks.
Ministry for Primary Industries readiness and response adviser Andre van Halderen said yesterday the ministry had received about 20 reports of suspected theileria infection on its pest and disease hotline and from veterinary laboratories, and was looking into each case.
"Based on feedback from local vets, it would appear there is an increase in the numbers of animals presenting with these symptoms this year," Mr van Halderen said.
The ministry was working with vets to gain an understanding of the risk factors at play and to exclude other causes.
The Veterinary Association's Northland regional chairwoman, Meredith Love, of Ruawai, said theileria had been discovered in Northland in the 1980s.
The number of calves that died in the past couple of months was low, but the way the disease presentation had changed was puzzling, she said. Vets were working with the Ministry for Primary Industries, Fonterra, DairyNZ and Beef+LambNZ to identify the infection, then control it, Ms Love said.
Broadwood beef farmer and Beef+Lamb Northern Region farmers' group chairman Laurie Copland said theileria had been around for a long time, but the difference this year was that calves were dying.
"A lot of farmers haven't reported it because they have had only two or three animals going down with it, but half a dozen calves have died on some farms."