Johne’s disease in dairy cattle
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, (MAP for short). It can survive in the environment in waterways, slurry, soil, dust, etc., but needs a host animal to multiply in.
The disease has a worldwide prevalence and has important economic implications for farmed livestock. It is estimated that over one third of UK dairy herds are infected to some extent, but within herd prevalence is difficult to ascertain, due to the relatively low sensitivity of most available tests, (ability to diagnose presence of the disease).
Johne’s disease results in financial loss to the farmer in terms of 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 and 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.