Johnes Disease

Johnes Disease is a chronic gut disease of cattle, sheep, goats and deer. In cattle it results in diarrhea, weight loss and eventually death.

Animals are usually infected in the first few weeks of life but do not develop clinical disease until they are 18 months or older.

Although wild life (e.g. rabbits) can act as a reservoir of infection the main source of spread is from the faeces of clinically infected animals (a cow scouring with Johnes disease can contain 100,000,000 organisms per gram of faeces). The organism can survive for a long time in the environment. Some calves can also be born carrying the infection and colostrum may contain Johnes disease organism.

Diagnosis of Johnes disease depends on 4 methods, blood tests, individual cow milk tests, culture of faeces or post mortem examination. Cows that are incubating Johnes disease are only likely to test positive on a milk or blood test in the few months before they become clinical.

There is no effective treatment for Johnes disease although vaccines are available to assist in the control of the disease.  Factors contributing to the increase of this disease include:-

1. Farms re-stocking after Foot and Mouth disease purchasing animals from several sources some of which may have been infected with Johnes.

2. The practice of feeding pooled colostrum to calves on dairy farms to reduce the incidence of calf scour. If some of the colostrum was contaminated this would be a very effective way of spreading the disease.

3. Larger herd sizes and fewer farm staff resulting in more cows being kept in larger calving areas and calves been left on cows for over 24 hours after calving.

For farms infected with Johnes disease the options of control and eradication were discussed. The advent of individual cow milk testing for Johnes disease (only picking up positives in the few months before becoming clinical) has made possible herd screening every 4 months. Any cows testing positive on a milk test should then be blood sampled at drying off to confirm the presence of the disease. Infected cows could then be culled or calved in separate calving boxes so as not to contaminate others and if served again they should be put to a beef bull. If necessary, animals of high genetic merit could be flushed to produce “clean” embryos.

VACCINATION

Vaccination can be used in heavily infected herds to reduce the number of clinical cases arising. Animals would usually be vaccinated in the first month of life but animals of any age can be vaccinated. Although vaccination does not eliminate the infection it will greatly reduce the number of clinical cases.