Clinical Examination of Farm Animals - CYF MEDICAL DISTRIBUTION

Clinical Examination of the Skin
coli septicaemia. Hair loss may appear to be getting
worse as the calf recovers from the primary
disease. Lesions, which may be seen on the head,
neck and limbs, are non-pruritic. Underlying nonpigmented
skin may appear pinker in colour than
normal. Visible hair growth resumes after a few
weeks.
Special diagnostic procedures
A firm diagnosis may have been made at this point,
but if not, further investigation may be required by
the use of special diagnostic techniques.
Bacterial culture
The normal bovine skin has a large population of
bacteria and fungi. The bacterial population rises in
wet weather and also in areas of the body where
sebuminous secretion occurs. The bacterial flora normally
live symbiotically with their host, but can be
opportunist pathogens if the body’s defences are
lowered in any way. Staphylococci, streptococci,
Arcanobacterium pyogenes and coliforms are commonly
found on the normal bovine skin, but heavy
growths of these organisms especially in pure culture
may be significant. Swabs from suspicious
lesions should be taken with care to avoid contamination
and processed quickly. Pustular material from
abscess may be aspirated by sterile needle and syringe
for culture. Skin biopsies may also be cultured.
Skin scrapings
These are particularly useful in the diagnosis of
mange infestation. They should be taken, if possible,
in the early stages of the disease. Later on very few
mites may be present as they encounter the skin’s defence
mechanisms. The scraping is best taken with a
scalpel blade to a depth at which signs of capillary
bleeding just appear. The scraping may be examined
microscopically directly or after treatment with
potassium hydroxide.
Skin biopsy
This is the most useful of the special diagnostic tests.
For good results it should be taken early on in the
disease process before secondary and possibly nonspecific
changes have occurred. Fully developed primary
lesions are particularly useful, and multiple
biopsies may also be helpful. If the biopsy is to prove
useful it must be taken with care. Asmall piece of skin
should be removed either by excision or by punch
biopsy. Before removal, hairs should be clipped short
and the skin gently cleaned with 70% alcohol, after
which local anaesthetic is instilled around and under
the proposed biopsy site. The biopsy should be
at least 5 mm in size and should be fixed in 10%
buffered formalin as soon as it has been taken. The
volume of fixative should be at least ten times that of
the biopsy.
Other diagnostic tests
Numerous other tests are available, including electron
microscopy for virus infections such as bovine
papular stomatitis. In other virus diseases with skin
lesions, serial serological samples may provide evidence
of recent infection.
CLINICIAN’S CHECKLIST
Have signs caused by the following causes of skin disease
been seen?
Parasitic causes
Bacterial causes
Fungal causes
Viral causes
Neoplastic causes
Nutritional causes
Toxic causes
Physical causes
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