Article By: Emma Tankersley Date: 9/07/2002 09:18:36 Source: Rural News

A NATIONAL survey to gauge prevalence of Johne’s disease in deer herds is essential, according to a paper by AgResearch, Invermay.

The paper was presented at last month’s New Zealand Society of Animal Production conference as part of a focus session on the disease.

The first confirmed case of Johne’s disease in deer was in the mid-1980’s and has since been found in over 300 deer farms. The paper said the disease appeared to be spreading rapidly and the number of serious outbreaks in yearlings and sporadic losses in adult deer is increasing.

Deer are susceptible to both cattle and sheep strains of the bacteria causing Johne’s disease. The paper said Johne’s could one day affect most deer farms because of the movement of deer between farms, the use of cattle and sheep to graze excess pasture on deer farms and because deer farms are usually created or expanded by taking on land grazed by sheep or cattle.

The paper advises farmers with herds not yet infected with Johne’s to keep a closed herd, avoid buying in animals and use artificial insemination to bring in new blood lines. It recommends farmers only buy animals from “low risk” herds and avoid grazing sheep and cattle unless they are known to come from “low risk” flocks or herds.

Control of Johne’s disease on infected farms is limited to management options like culling infected stock and test-positive animals, or depopulating and restocking after two years.

Vaccination is likely to be the most cost-effective method of long-term control.

The paper said a market assurance programme might be a way to identify and certify “free” or “low risk” farms and provide the industry with “clean” animals.

The programme would be an essential step to reduce spread of the disease from infected farms. Farmers would know their status and manage their herd accordingly, a “low risk” status could enhance the value of the farmer's flock, and “low risk” farms might be able to export venison to a lager range of markets overseas in the future.

However some farmers might not want to know their status because of the stigma from having an infected farm, the report said.

Until effective control or eradication measures are developed there is little incentive for farmers to join a market assurance programme unless there is a very large premium for “low risk” animals or animal movement restrictions are placed infected or untested herds.

The report said the actual prevalence of infected herds would determine a market assurance programme viability because if true prevalence was too high, few farmers would be interested in joining the programme because they would be unlikely to be free of the disease.

There are over 300 deer farms - about 5% of the national herd - on which Johne’s had been confirmed but the true prevalence is likely to be greater, the report said.