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JOHNE ’ S D I SEASE
WINTER 2011 ISSUE
LIVESTOCK MATTERS
24
Testing for Johne's disease
Keith explains: ‘Unlike other infectious
diseases - BVD, IBR, etc - the aim with
Johne's disease is, initially, simply to establish
whether it is present or not.’
A variety of laboratory tests are available to
test for Johne's disease, and on dairy farms,
whole herd antibody screening can easily
be carried out on milk samples. Animals
suspected of being clinically affected should
be tested as a priority.
‘The nature of the disease means that
evidence of the bacterium is not always
present in infected animals, all of the time,’
explains Keith. ‘Hence ongoing testing is
important. Targeted routine screening should
be carried out and include animals which
are not performing to their potential, and
any cull animals.’
The risk factors which increase the likelihood
of Johne's disease being present are shown
in Table 1.
If the presence of Johne's disease is
confirmed in a herd, then a control
programme needs to be put in place to
prevent the infection spreading.
‘Repeated testing of adult animals can
identify individuals which are likely to be
infected allowing them to be managed
differently to reduce the threat they pose
to other animals, particularly young calves,
on the farm.
‘Ideally, all infected or suspect animals will
be culled before signs of clinical disease
are seen so that they are not spreading the
infection into the farm environment.
However, in the early stages of a control
programme, there may be too many high
risk animals to make culling them all an
economic option.
‘So where the number of infected cattle is
high, then high risk cows should be calved
separately from the herd,’ see Table 2.
‘Feeding a good quality milk replacer
rather than pooled colostrum and waste milk
will further reduce the risk of transmission.
In heavily infected herds, then 'snatch
calving' reduces the risk of newborn calves
being infected by their dam - they can
either be given powdered colostrum or
colostrum from known donor cows of high
health status.
‘The calf is most vulnerable to infection in
its early life. So once in the rearing
accommodation, it is vital to maintain good
hygiene to reduce the level of challenge
as much as possible.
‘Calves should also be kept away from
the faeces of older animals. Ideally, when
calves are turned out in the summer, they
should not be grazed on land onto which
slurry or dung from older animals has
been spread.’
Disease control strategies
Table 1: Risk factors for
Johne's disease
l
Intensively managed herds
l
History of bought-in animals
l
Communal calving yards
l
Feeding pooled colostrum to calves
l
Contracting out heifer rearing
l
Spreading of slurry/FYM from
other farms
Weight loss and scouring are the classic signs of clinical Johne's disease
but there is also reduced productivity in the pre-clinical phase.
Cattle can become infected with Johne's disease
at any age, although infection in the first few
weeks or months of life is most common.
Biosecurity protocols
Whether Johne's disease is present or not,
biosecurity protocols should be instigated
to protect the herd.
‘Due to the long incubation period of the
disease, buying-in policies should give
preference to animals bred and reared
in herds which have an active Johne's
disease surveillance and management
policy. The longer such a surveillance and
management policy has been followed,
the better.’
Know your herd's
Johne's disease status
Keith concludes: ‘In the case of Johne's
disease, ignorance, most definitely, is not
bliss. Determining whether your herd is
infected requires a different tack to testing
for BVD or leptospirosis. Farmers should
talk to their vet about investigating the
herd's Johne's disease status, if it is not
known. If the disease is confirmed, then
they can advise a control strategy to
reduce the spread of infection and limit
production losses.
‘If the herd tests free of the disease, then
biosecurity protocols to safeguard the herd
from future infection will be needed along
with an ongoing screening programme.’
Table 2: Action plan for high
risk Johne's disease cows
l
Calve cows in isolation from others
l
Clean and disinfect pens between use
l
Clean cows' teats before calving
l
Feed colostrum only to their calf
l
Do not feed waste milk to other calves
l
Consider pasteurisation of colostrum