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Symptoms
Johne’s disease in cattle is a chronic wasting disease
with long lasting diarrhoea and weight loss despite good appetite,
which results in eventual death. It is usually seen in cattle
aged 3-5 years and often older, but rarely in younger cattle.
Incubation
The incubation period is long (from one to many years). This
means that some cattle can be infected and never develop symptoms
of the disease, but they are still capable of spreading infection
through the herd. Johne’s disease can therefore be present
and spreading within the herd long before the farmer is aware
of it. Often cattle develop symptoms after a period of stress
such as calving, or movement to another farm, or a period
of work in the case of bulls.
Susceptible animals
Calves up to 30 days old are extremely susceptible and then
they slowly develop a resistance as they get older. After
12 months they become increasingly resistant so it is rare
for adult cattle to pick up the infection.
Introduction of infection to a herd
Buying an infected animal that is not yet showing signs of
disease is the usual way infection is introduced to a herd.
Herds Affected
Because of the long incubation period and the fact that young
cattle are the most susceptible to infection, the impact of
the disease in beef herds is greatest in those which breed
their own replacements. Once infection is introduced to such
a herd, the disease will become more firmly established as
years go by with an increasing number of losses, unless control
measures are taken.
Spread of infection within the herd
Cattle are infected by ingestion (taking in by mouth) of the
organism which is present in the faeces (dung) of an infected
animal. One gram of faeces from a clinically affected cow
can sometimes contain over 5 million Johne’s bacteria
and less than 1000 of these bacteria are necessary to infect
a young calf. Calves are at risk when sucking contaminated
udders and when exposed to contaminated water or food sources.
Modern husbandry methods of loose housing large numbers of
cows and calves together can increase the spread of the disease.
The bacteria can survive on pasture for up to 12 months and
in water up to 17 months. Some infected cows shed the bacteria
in their colostrum and milk and sometimes calves can be infected
through the uterus prior to birth. Therefore an infected cow
is highly likely to pass the infection on to her calf.
To prevent introduction of infection
to a herd
It is most important to avoid buying in infected cattle. This
means cattle of unknown status should be isolated and tested
before being introduced to the herd. However because the tests
will not pick up every animal in the early stages of incubation,
knowing the disease status of a herd is of more value than
the test results of an individual animal. Therefore the safest
cattle to buy are those from herds which are ‘Accredited
Monitored Free of Johne’s disease’.
Control of Johne's disease
The basics of control are to identify and cull infected cattle,
(any offspring of infected cows should not be retained for
breeding either) and new infections must be prevented. Therefore
elimination of Johne’s disease from a herd requires
a thorough understanding of the disease by the farmer, close
co-operation with his veterinary surgeon and regular blood
testing of the herd. Half-hearted attempts at control will
generally fail.
Identifying infected animals
All animals 2 years of age and older are blood-sampled and
the samples are laboratory tested (ELISA test) for Johne’s
disease. All animals that test positive should be culled or
separated from the rest of the herd until they can be culled.
The blood test will not always pick every animal in the earlier
stages of incubation, but as they become nearer to showing
signs of the disease the detection rate increases up to 90%.
So, after culling positive animals there can still be infected
animals in the herd. However these animals in the early stages
of disease are not shedding such large numbers of organism
and are a lower risk, as a source of infection to other cattle.
Nevertheless it is important to understand the risk that
these infected test negative animals present in prolonging
the infection in a herd. Because of this it is essential to
introduce measures to prevent new infections. It also means
that a test and cull programme will of necessity take several
years.
Prevention of new infections within
the herd
This is based on reducing the risk as far as possible of calves
under 1 year old, especially the youngest calves, being exposed
to Johne’s disease organisms which are being shed in
the faeces of an infected animal.
Isolate immediately any animal showing symptoms suspicious
of Johne’s disease (scouring and weight loss) and test.
Isolate and test bought in animals unless they come from
an accredited monitored free herd.
Good isolation premises are essential and animals should be
kept there until all results of tests are known.
Cull or separate from the rest of the herd all animals positive
to the ELISA test.
Cull or do not retain in the breeding herd any offspring
of positive cows.
Fence off any areas of stagnant or slow moving water which
can become fouled and is used as a drinking source and provide
piped water. If this is not possible avoid grazing any suckling
calves which are potential breeding stock in areas where such
water is to be found.
All water troughs should be checked for signs of fouling
by adult cattle and cleaned out regularly.
Winter housing should be looked at to reduce the risk of calves’
water or food sources becoming fouled by adult cattle. Water
troughs can be raised to a level which will prevent access
by young caves and reduce the risk of fouling and the calves
can be given a separate water trough in their creep area.
Lying areas for cows should be as clean/well bedded as possible.
Cows that will not lie in cubicles will have very dirty udders
and should be housed elsewhere.
Calving pens should be cleaned or well bedded with fresh
straw between occupants.
If possible change calving period so that cows calve outside,
otherwise turn calves out as soon as possible after calving.
Suckling calves should not be grazed on land which has recently
had cattle manure spread on it.
Manure from isolation premises which have contained a confirmed
case of Johne’s disease should never be spread on the
land (should be burnt etc.).
Of lesser risk is possible infection from sheep, goats, rabbits,
deer etc. – it is more likely for them to become infected
from cattle than vice-versa.
Avoid grazing sheep and suckling calves together.
Do not house cattle and sheep together in the same shed.
Do not spread manure from the sheep shed on pastures to be
grazed by suckling calves.
Work closely with your veterinary surgeon seeking his advice
in relation to the above measures and any other steps he/she
may consider appropriate in your case.
Vaccination
Advice must be sought from your veterinary surgeon regarding
the use of vaccine.
In heavily infected herds vaccination is a useful method
of reducing the number of clinical cases and therefore reducing
the amount of infection in the environment.
Calves should be vaccinated in the first week of life and
vaccination should continue until no clinical Johne’s
disease has occurred for at least 2 years. When combined with
good husbandry and hygiene measures (ie. care in preventing
spread of infection as outlined above) it can be an effective
method of control. Vaccinated animals are less likely to develop
clinical symptoms of Johne’s disease but they can still
become infected and shed the infective organisms and therefore
there is a danger of the disease remaining in the herd albeit
at a lower level.
Salvage of genetic material
Serious attempts to control or eliminate Johne’s disease
can involve the culling of valuable breeding stock. Genetic
material can be saved by the use of artificial breeding. Both
semen and embryos are considered to be low risk of spreading
infection. Clean recipients are obviously necessary for this
approach.
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