PCR which takes 1-2 days. It is a sensitive test, but fairly expensive. An ELISA detecting antibody response has been validated for cattle, and is useful for the testing of suspect clinical cases. However this test is only of value in animals more than 2 years of age and even then only detects 80% of clinical cases and 20% of subclinical cases. A bulk milk tank ELISA is valuable as a herd screen to test of the presence of Johne’s disease. The cost is modest and so it is worth doing on a regular basis.
Controlling disease
As it is not possible to detect 100% of infected cattle with confi dence, the aim is for damage control.
Hygiene and management are important control measures. The idea is to reduce exposure to the bacterium (to reduce infection) and to reduce stress (to reduce the development of clinical disease).
Recommended practise is:-
• Avoid faecal contamination?! • Clean calving pens thoroughly • Keep young stock separate from adults • Only feed dam’s colostrum or use artifi cial free-dried colostrum. • Do not feed pooled colostrum of waste milk. • Avoid contact with sheep, deer and rabbits.
Biosecurity
When purchasing animals it is diffi cult to prevent buying in Johne’s disease. There are very few certifi ed clean herds. Testing individual animals is not especially useful given the low sensitivity of most tests. In pedigree herds in which there are no clinical cases of Johne’s disease, individual testing of animals and culling positive ones may be
feasible and lead to accreditation. Vaccination is now an option. The vaccine (Gudair) is not licensed in this country, but can be imported. In a herd in which Johne’s disease is prevalent, many calves will be infected at birth, so we will be vaccinating infected animals. Therefore the vaccine will not be preventing disease, rather modifying the clinical outcome of infection, reducing clinical signs and reducing bacterial shedding in the faeces and thus reducing the bacterial load present on the farm. In herds in which clinical Johne’s disease is regularly seen, it is recommended that all adult cattle on the farm are vaccinated and then all replacement animals between the fi rst 2-3 weeks and 6 months of life. The benefi ts of vaccination are a reduction in mortality and clinical disease, a regression of lesions with a reduction in shedding of Map and extension of productive life with an improvement in milk yields. One of the disadvantages of vaccination is that tests cannot tell vaccinated animals from animals with natural infection. There is also potential for interference with the interpretation of tuberculosis testing. In the future, with improvements in the understanding of genetics, we may be able to breed for resistance to Johne’s disease, but this would be a long term control measure and the decrease in disease prevalence would be slow.
Reliable cost effective options for
Milk Recording and Disease Testing with integrated management tools
Contact us on 01923 695319 Email:
info@thecdi.co.uk www.thecdi.co.uk
THE JOURNAL OCTOBER 2009 00
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