6 CUMBRIA FARMER May 2009VetsTalk
Hidden lamb menace
difficult to diagnose
Vet Colin Lindsay explains why sheep farmers
need to keep a wary eye out for border disease
B
order disease is a
viral condition of
sheep that was first
reported in the bor-
ders of England and Wales
in the 1950s. Since then, the
disease, which shares a lot
of characteristics with BVD
in cattle, has been recog-
nised worldwide.
It can cause a variety of
problems, the main one being
infertility, abortions and
abnormalities in lambs
(`hairy shakers').
The number of reported
outbreaks in the UK are low.
There were 18 outbreaks in
2000. This shot up to 37 in
2004, but dropped to 24 in 2007.
However, within the prac-
tice this lambing season alone
we have had two confirmed
outbreaks and five suspected.
Often, the first sign of the
disease is a low scanning per-
centage; this can then be fol-
lowed up by abortions.
On a national scale, the
number of outbreaks is signif-
icantly less important than
toxoplasmosis or enzootic
abortion, which account for
more than 75 per cent of abor-
tions. But on an individual
farm basis, it can be devas-
tating.
In one outbreak this year,
scanning percentages were
reduced from 180 down to 125
per cent.The subsequent
lambing was also fraught with
problems, including abortions
and weak, non-viable lambs
that couldn't stand. This
accounted for another 20 per
cent of the lamb crop. This
brought the lambing percent-
age down to around the 100
percent mark.
Some of the lambs that did
survive have uncontrolled
tremors. These can vary from
a barely detectable fine trem-
bling of the head, ears and tail
to violent, rhythmic contrac-
tions of the muscles of the
hindquarters. Abnormalities
of the fleece are characterised
by fine coats and longer guard
hairs. These lambs are known
as hairy shakers.
Some of them also have a
dished face or long legs and a
short body, looking more like
a goat kid than a lamb.
These tremors can resolve
with time, but do reappear
during periods of stress, such
as gathering.
With the fullness of time,
some of these lambs will fail
to thrive, develop a severe
scour and die.
Border disease is spread by
close contact from sheep to
sheep � in saliva and nasal
secretions.
If a healthy, non-pregnant
animal is infected, they will
develop a slight temperature,
and, over a period of one to
two weeks, rid themselves of
the infection. During this
period, however, they will be
excreting the virus.
The most serious problems
arise when pregnant animals
are infected. The outcome of
this depends upon the stage of
pregnancy when the infection
occurs.
The unborn lamb's immune
system starts to function
around day 85 of the pregnan-
cy. If infection occurs after
this, as the virus crosses the
placenta into the lamb, the
lamb's immune system is
active and reabsorptions or
abortions are rare.
If, however, the virus cross-
es the placenta before day 85,
there can be a variety of out-
comes, including the reabsorp-
tions, abortions and hairy
shakers discussed earlier. The
real menace are the lambs that
look normal but are carrying
the virus for life. They are a
constant source of infection to
the rest of the flock and are
called persistently infected
lambs or PIs for short.
Flocks that have never
experienced border disease
are particularly vulnerable to
the buying in of PIs in the
form of breeding tups or
gimmer replacements.
Diagnosis can be difficult,
particularly if the key signs,
such as hairy shakers, aren't
recognised.
Poor scanning percentages
can be confused with infertile
tups, mineral deficiencies,
poor ewe condition, fluke or
even inexperienced tup lambs,
so it is easily missed.
Abortions can be confused
with enzootic abortion and
toxoplasmosis. Weak lambs
can arise from enzootic abor-
tion, toxoplasmosis, mineral
deficiencies, poor live weights,
and poor ewe condition.
As we progress through to
scour and ill thrift, again this
can be confused with mineral
deficiencies, coccidiosis,
worms, fluke, bad breeding etc.
Diagnosis is achieved by
blood samples or post
mortems. But do take care
and speak to your vet first.
Control consists of blood
sampling and eradicating any
PIs. There is no licensed vac-
cine on the market for its con-
trol or prevention.
Prevention consists of main-
taining a closed flock, buying
from a clean source or blood
sampling replacements before
mixing with your own flock.
Again, speak to your vet.
Hairy shaker: A lamb with border disease
PRACTICE NOTES
CAPONTREE Veterinary Practice at
Longtown, Brampton and Haltwhistle
has grown over the years to provide a
dedicated service to farm, equine and
companion animals with vets
specialising in each of these areas.
It aims to provide a whole farm approach
to improve health, profitability and
productivity.
The practice always works to provide a
personal and professional service for all of its
clients, with a 24-hour emergency call-out
provided by the veterinary surgeons working
in the practice.
`The menace are the lambs that
look normal but are carrying
the virus for life. They are a
constant source of infection to
the rest of the flock'

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