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Johne’s Disease: Cause, how it spreads and financial losses

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Ingestion of Johne’s bacteria via colostrum or milk from an infected dam is a primary source of infection for calves, writes Stephen Gilkinson, dairying technologist at the College of Agriculture, Food and Rural Enterprise (CAFRE).

Ingestion of faeces from infected bedding material in calving pens, is also a risk, hence hygiene around calving is extremely important.

A calf may also get infected in the wombdepending on how advanced the disease is in the dam. Replacement heifers that get infected in utero, via infected colostrum/milk, or via the ingestion of faeces from their environment, can subsequently pass the bacterium on to their herd mates through faecal shedding. By so doing, ensure that the disease persists in a herd and the cycle from dam to calf continues.

Calf disease prevention will be explored during the final CAFRE Calf 2020 webinar on Thursday, December 3rd, starting at 8.00 pm. Full details of the webinar and how to join are available from the News and Events section of the CAFRE website.

Causes of Johne’s Disease 

Johne’s disease is a bacterial disease of ruminants and other (mainly) mammals, for which there is no cure. The organism has been found in wildlife as well as domesticated animals.

It is caused by the bacterium Mycobacterium avium subspecies paratuberculosis or MAP for short.  It can survive in the environment in waterways, slurry, soil, dust, etc., but needs a host animal to multiply in.

Impacts 

Johne’s disease results in a financial loss to the farmer:

  • Lower milk yields;
  • Higher somatic cell counts;
  • Increased mastitis;
  • Reduced fertility;
  • Increased susceptibility to other diseases;
  • Increased culling for all the aforementioned reasons;
  • Lower cull cow value;
  • Eventually death in animals that are in the final stages of the disease

The cost of the disease per unit of livestock is very difficult to ascertain, as it can often be masked in some, or all of the parameters just mentioned.

What can farmers do?
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Herd testing for the disease is a must to ascertain prevalence level.  This can be an annual blood test or quarterly milk sampling from milk recording.

Because these tests are poor at picking up positive animals in the early stages of the disease, repeat testing is necessary to determine the likelihood of an animal being positive, before any culling decisions are made. Faecal testing can be used as another tool to aid positive diagnosis.

Cows with an uncertain Johne’s diagnosis should be marked, (red ear tag or similar). If these animals are in-calf, they should be calved away from the main herd.

The calf removed immediately and fed colostrum from a cow that is negative for the disease.  (Have a stock of frozen colostrum for this).

Cows considered Johne’s positive, (as determined by at least two positive tests by whatever method(s)) should be culled. They are likely to be ‘spreaders’ and potentially infect their offspring, either in utero or in colostrum at birth.

Veterinary advice should be sought and followed regarding this disease.

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