Johnes Disease and your Dairy Herd
What is Johnes Disease?
Johnes disease is a bacterial infection that causes severe diarrhoea and wasting in adult cattle. Cows are infected at a young age and incubate the disease over several years shedding bacteria and infecting other cattle and pastures. As they get older the disease develops to an end stage where the cow will develop severe watery diarrhoea and lose dramatic amounts of weight and need to be euthanased on welfare grounds. Calves often are infected either by eating infected faeces or when they suck an infected cow shortly after birth. It is a slow disease to develop and a particularly difficult bacteria to eradicate – it can live for 2-4 years on the pasture and for 9-12 months in slurry.
Often you will only see the end stage disease in which a cow develops liquid diarrhoea and rapidly loses weight and requires euthanasia. However remember that this is only the tip of the iceberg. It has been suggested that for every end stage clinical case there are 18- 25 subclinical cases in the herd! Clinical disease tends to be seen in older cattle but remember they tend to be infected as a calf so one clinical case can indicate a bigger potential problem under the surface.
Infected animals are also much more prone to other diseases.
If you have ever had Johnes disease diagnosed on your farm it is likely you have several other cows infected sub-clinically in your herd. It was estimated in a recent study that 34.7% of UK dairy farms had been exposed to Johnes disease.
Estimates are around £30 per cow per year in an infected herd. This is through replacements, loss of production and increased susceptibility to other diseases. That is around £4500 per year for an average 150 cow dairy herd. Remember this can be much worse if infection is widespread.
Johnes Disease is diagnosed via either a faecal or blood sample from clinically sick animals or more simply and usefully individual milk samples can be taken to test for the presence of Johnes disease in your herd before the cow becomes clinically ill. It is essential to test regularly as levels of antibody fluctuate in infected cows. The more often you test the more likely you are to find it.
There is no treatment for Johnes disease. Attempting to eradicate the disease from your farm is probably the most effective way of control.
Cows with clinical Johnes disease will not survive and need to be euthanased for humane reasons.
Animals can be vaccinated against Johnes disease. However the vaccination is dangerous to humans and can interfere with the interpretation of TB tests. It is also expensive and doesn’t tend to significantly reduce the number of infected animals. Eradication from the herd is therefore a sensible way to control johns on your farm.
How can you control Johnes disease? It does take some effort but the following measures should help keep the disease under control.
- Identify Johnes positive animals through regular testing. Placing a red management tag in their ear or freeze branding them with a letter J or both.
- Keep Johnes positive or inconclusive animals away from calves- keep them away from your usual calving shed and avoid calves coming into contact with their milk and faeces.
- Put Johnes cows on an accelerated cull list- don't hang onto them if they have problems!
- Don’t retain calves for breeding that have come from infected stock– they will also be likely to be infected.
- Keep cows and calves environment as clean as possible and try to reduce faecal contamination.
- Keep food and water troughs clean and free from faecal contamination.
- Provide mains water and fence off other water sources
- Spread dung on arable land not used for grazing and don’t graze ground which has had slurry spread on it for at least 1 year
- Pooled colostrum can act as a source of infection for many calves – discuss with your vet the best colostrum strategy.
- Continually test and monitor and remove infected animals. Your vet will be able to discuss with you a suitable testing regime