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Mycotic
dermatitis (Dermatophilosis) of sheep
E-mail contact: Dr
Ray Batey
Austbreed's
veterinarians are contactable through: frontdesk@austbreed.com.au
or visit
our website: http://www.austbreed.com.au
Ovine dermatophilosis
('lumpy wool', 'dermo') is well known to Merino sheep producers
in higher rainfall areas of Australia. It is mainly recognised
by scabs and matted wool, usually over the back, which makes shearing
difficult and predisposes animals to blowfly strike.
There are many misconceptions
about this disease, and some of the following points may help
with understanding it.
- Dermatophilosis
is seldom recognised in its milder form which includes small
scabs on the non-wool areas of the ears, face and legs. However,
these chronic lesions are important as the reservoir of infection
in a flock.
- New infections occur
via spores which are released when infected scabs become wet.
These then infect wet wool or skin on new hosts. Thus, moving
or yarding wet sheep together, favours transmission.
- Older sheep may
be immune in infected flocks, and young sheep tend to be more
susceptible.
- Many mild to moderate
cases of true 'lumpy wool' self cure, and there is no need for
treatment.
- Our experience is
that lambs may become infected from their mothers, but these
lesions often heal without treatment.
- Some wool types
might be more prone to infection- especially the broader more
open types. However, such animals are generally not suited to
higher rainfall regions.
- Susceptibility to
'lumpy wool' is NOT inherited, and therefore, culling affected
ewes or rams will not reduce the occurrence in the flock.
- The only effective
means of reducing prevalence of infection is for the whole flock
to be dipped with cetrimide-zinc sulphate. This can be used
alone or mixed with organophosphate or synthetic pyrethroid
chemicals. An alternative is to use a magnesium fluorosilicate-sulphur-rotenone
dip which is available commercially in Australia. Contact
us or your local vet for further advice on these products.
- Treatment with zinc
sulphate will NOT cure cases of 'lumpy wool'.
- Treatment with antibiotics
is ONLY of value in enabling infected sheep to be shorn. In
most situations, there is NO other reason to administer antibiotics
to 'dermo' sheep or lambs.
- Treating affected
individual sheep does not reduce prevalence
- Treating with antibiotics
has included the use of penicillin-streptomycin at high dose
rate. Not only is this unnecessary in many cases, it also presents
the risk of prolonged tissue residues of streptomycin. Injectable
streptomycin is no longer permitted to be used in food-producing
animals in many countries and has been withdrawn from the market
because of these concerns. Contact
us or your local vet for advice on alternative treatments
for individuals to enable shearing.
- Mycotic dermatitis
needs to be approached as a management problem- with emphasis
on effective risk management.
We can provide advice on this.
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