13June 2009 CUMBRIA FARMER FlockHealth
What causes sheep to abort?
T
his is a busy time of year
at Merrythought, with
examination of ovine
abortion material form-
ing a large part of our work.
As always, it is advisable to sub-
mit material when more than two
per cent of ewes in a group have
aborted or when abortions occur
in clusters. Both scenarios sug-
gest an infectious cause.
A range of tests are undertaken
on samples from the foetus and the
placenta. It is important that both
are submitted where possible. Rea-
sons for not reaching a diagnosis
include decomposition and failure
to submit both samples.
This season, a diagnosis was
made in 67 per cent of cases sub-
mitted � above the national average.
Where the cause has been deter-
mined, it is important to discuss
with your vet whether any spe-
cific action should be taken to pre-
vent future outbreaks. This may
include advice on vaccination,
feeding practices and sourcing
replacement breeding stock.
As always, despite availability
of good vaccines, chlamydophila
abortus (EAE) and toxoplasma
gondii remain the most commonly
diagnosed causes of abortion in
our flocks, accounting for more
than two-thirds of diagnoses.
There have been surprisingly
few diagnoses of campylobacter
abortion in the region this year.
Campylobacter has been the third
most common cause of abortion in
the UK for the past nine years,
typically accounting for about 12
per cent of diagnoses reached.
A possible explanation for this
decrease is the widespread use of
snacker systems to feed ewes.
Gatherings of carrion crows
around troughs have been asso-
ciated with the mechanical spread
of this disease. Closed flocks also
have less risk as the disease is
usually introduced by healthy car-
rier ewes, shedding the bacteria
in their faeces.
Border disease (BDV) has been
diagnosed more frequently as a
cause of abortion this year.
BDV is caused by a virus, relat-
ed to the bovine viral diarrhoea
virus, and can cause a variety of
signs depending on the stage of
pregnancy at which ewes are
infected. Early in pregnancy,
infected ewes may be detected by
an increased barren rate at scan-
ning.
Lambs born from ewes infected
before day 85 of gestation are per-
sistently infected. They may have
subtle fleece changes and may
tremble, the so-called `hairy shak-
ers'. Some will appear normal, but
shed high levels of virus, making
them a source of infection for the
rest of the flock.
Lambs born from ewes infected
after 85 days of gestation have
usually developed antibodies and
are healthy.
This year, we have seen BDV
causing abortions in flocks with
poorer lambing percentages than
usual.
We have also seen lambs born
with hairy fleeces, abnormal con-
formation of the heads and low
birth weights in persistently
infected lambs. BDV is usually
introduced into flocks by pur-
chase of persistently infected (PI)
rams or replacement females. Pre-
purchase testing is advisable. A
simple blood test can determine if
a sheep is a PI.
There are many bacterial caus-
es of abortion and this year we
have seen an increase in abortion
due to e-coli. In previous years
this has been diagnosed as a spo-
radic cause of abortion within
flocks. This year, we have diag-
nosed it in submissions from 12
holdings, most of which were low-
land flocks.
Many of the common causes of
abortion have zoonotic potential �
that is they can cause disease in
humans � so great care should be
taken when lambing sheep and
handling live vaccines for EAE
and toxoplasmosis. In particular,
pregnant women should not come
into contact with lambing ewes.
Rebecca Mearns, of the Veterinary Laboratories Agency, near Penrith, looks at the
diagnoses made from submissions to the agency in the first four months of the year
Happy outcome... But not all ewe pregnancies result in healthy lambs like this pair

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