Infectious causes of abortion are most common after day 100 of
pregnancy. While sporadic losses are variably attributed to
handling procedures or movement, an abortion rate in excess of two
per cent is suggestive of an infectious cause and veterinary
investigation is essential at an early stage. Enzootic abortion of
ewes, Toxoplasma gondii and Campylobacter species cause
over 80 per cent of abortion outbreaks in the UK. The cost of
abortion is variably quoted as £85 per aborted ewe.
General principles - Biosecurity and
Biosecurity and biocontainment are
buzz words in agriculture but are often forgotten during a trip to
the market or on a busy day at lambing time. Such sound principles
are integral to the success and profitability of your farm and must
never be dismissed as interference.
Fig 1: All abortions should be thoroughly
investigated - each costs you around £85
Fig 2: The most common causes of abortion are
readily prevented by vaccination
introduction of new diseases onto your farm from outside
Freedom from most infectious
causes of abortion is best achieved by maintaining a closed clean
Reduce/prevent the movement
of infectious diseases on your farm.
In common with all infectious
causes of abortion, aborted ewes must be isolated and aborted
material and infected bedding removed and destroyed to prevent
spread of disease on your farm. Ewes that give birth to dead/weakly
full-term lambs should also be isolated. Ewe lambs fostered on to
aborted ewes should not be retained for future breeding.
Fig 3: All aborted ewes must be isolated and
aborted material removed and destroyed
The potential of many
abortificacient agents to infect humans (zoonotic infection) must
be stressed to everyone attending sheep on your farm. Appropriate
hygiene precautions must also extend to all households where
infection could arise from farm workers' contaminated clothing and
Diagnosis of the cause(s) of
The minimum requirement for
laboratory submissions for abortion diagnosis includes the
fetus(es) or fetal stomach contents, a piece of placenta, and a
maternal serum sample collected by a veterinary surgeon as part of
their investigations. While the first submission may identify a
recognised cause, it is important to continue collecting aborted
material during the outbreak as more than one agent may be present
within the flock and such knowledge is essential when formulating
treatment, control and prevention strategies.
Fig 4: Purchase accredited stock and vaccinate them
against EAE and Toxoplasmosis - a small insurance premium on an
likely outlay of £120
plus for top quality ewe lambs in
COMMON CAUSES OF ABORTION
Enzootic abortion of ewes, Toxoplasma
gondii and Campylobacter species cause over 70 per
cent of abortion outbreaks in the UK.
Chlamydial abortion, Chlamydophila
abortus, enzootic abortion of ewes (EAE),
Pregnant women are at serious
risk from C. abortus infection (zoonotic infection).
Despite the availability of a highly efficacious vaccine, EAE is
still the main cause of ovine abortion in the UK. Disease is
acquired from exposure of susceptible sheep to high levels of
infected uterine discharges and aborted material. Infection does
not result in abortion during that pregnancy unless the ewe is more
than six weeks from her due lambing date rather infection remains
latent in the sheep until the subsequent pregnancy then causes
Fig 5: Mummified fetus
in an abortion caused by Toxoplasma gondii.
Fig 6: All sheep feed should be stored in
vermin-proof facilities to prevent contamination by cats and other
Infection typically results
in the abortion/birth of fresh dead and/or weak lambs during the
last three weeks of gestation. The ewe is not sick and may only be
identified by a red/brown vulval discharge staining the wool around
the tail/perineum, and a drawn-up abdomen. Live lambs rarely
survive more than a few hours despite supportive care.
Whole flock long-acting
oxytetracycline injection (20 mg/kg) is an emergency measure that
may reduce the number of abortions from C. abortus
infection, but such treatment cannot reverse placental damage with
the result that lambs are carried closer to term but remain weak at
birth with consequent high mortality. Antibiotic use in agriculture
is coming under intense scrutiny and whole group injection can only
be justified as an emergency measure then vaccination must be
In common with all infectious
causes of abortion, aborted ewes must be isolated and aborted
material and infected bedding removed and destroyed. Ewes that give
birth to dead/weak full-term lambs should also be isolated. Lambs
fostered on to aborted ewes should not be retained for future
Freedom from C.
abortus infection is best achieved by maintaining a closed
clean flock with strict biosecurity measures although there have
been rare situations where infected material has been transmitted
between neighbouring farms by birds/foxes.
Various accreditation schemes
are operating which offer breeding female replacements from flocks
monitored free of C. abortus infection.
Vaccination offers an
excellent means of control for farms buying breeding replacements
from non-accredited sources, and in those flocks with an endemic
C. abortus problem. Vaccination of sheep already infected
with C. abortus will not prevent all abortions but can
reduce the incidence.
The "gold standard" would be
to purchase accredited stock and vaccinate them against C.
abortus. Vaccination against C. abortus costs £2-3
per dose but this cost must be divided over the ewe's productive
life (three pregnancies at least). The cost of abortion is
variably quoted £85 per aborted ewe.
Fig 7: Campylobacter species are a common cause of
abortion particularly where sheep are managed intensively leading
to heavy pasture contamination during late
People with an
immunosuppressive illness are at risk of illness. Infection of
susceptible women during pregnancy can result in infection of the
fetus causing serious eye and brain damage.
Fig 8: Sheep grazing a field where run-off from a
cattle midden has collected posing a significant disease
Toxoplasmosis results from
infection of susceptible sheep with the protozoan parasite
Toxoplasma gondii. The sexual cycle takes place in cats
while the asexual cycle can occur in a range of species including
sheep. Infection during early pregnancy may be manifest as
embryo/early fetal loss with an increased number of returns to
service after an irregular extended interval or an increased barren
rate, often above 8 to 10 per cent. Often the highest number of
barren sheep is in the youngest age group. Toxoplasma infection
during mid pregnancy results in abortion or production of weakly
live lambs near term often with a small and leathery mummified
Fig 9: Seabirds can be a significant source of
certain Salmonella species - feed on a clean
area of the field every day
Diagnosis of toxoplasmosis is
usually based on identification of spefic changes in the placenta
in combination with the detection of high levels of antibodies in
ewe blood. Antibody may also be present in the fetal fluids and can
also be detected in newborn lambs before they have sucked
colostrum. Blood sampling of the ewe alone is not sufficient as a
positive result merely indicates past infection not that the
current abortion is due to toxoplasmosis.
All sheep feed should be
stored in vermin-proof facilities to prevent contamination by cats
and other vermin. Vaccination provides excellent immunity to
natural infection and should be administered at least three weeks
before the breeding season. Care should be taken when administering
the vaccine; the detailed safety instructions provided by the
manufacturer should be followed closely. The vaccine costs £3 per
dose but as a single vaccination effectively provides lifelong
immunity this amounts to a cost of 50 to 60 pence per
subspecies fetus and Campylobacter jejuni are
common causes of abortion, particularly where sheep are managed
intensively leading to heavy contamination and unhygienic
environments during late gestation. The main source of infection is
purchased carrier sheep. The common presentation is abortion during
late gestation although some lambs are carried to full-term and are
born weak and succumb soon after birth.
All aborted ewes must be
isolated immediately and the main flock moved to other
accommodation/pasture whenever possible. Treatment options are
limited because infection has already spread rapidly through the
group by the time the first abortions are recognised.
Sheep should be managed in
clean environments and not subjected to unhygienic conditions
especially during late gestation. Particular attention should be
paid to the feeding troughs/areas. Purchased sheep must be managed
as a separate group until after lambing. Following infection, ewes
are immune to further challenge and will not abort. A vaccine can
be imported into the UK under licence.
Montevideo, Salmonella Dublin and Salmonella
Typhimurium have been associated with abortion and death in
pregnant ewes. Sheep may simply be found dead with rotten lambs
still present in the womb.
There are many potential
sources of salmonellae in a group of sheep including contaminated
feedstuffs and water courses, sewage effluent overflow, carrier
cattle, and carrion. All feed must be stored in vermin-proof bins
but this is rarely achieved on many farms. Sheep should be fed in
troughs that are tipped over and moved immediately after feeding.
When sheep are fed using snackers, a clean area of the field must
be used every day but this advice is often ignored. Wherever
possible, water should be supplied from a mains supply with ponds
and surface water fenced off. If possible pregnant sheep should be
managed separately from cattle.
There is a significant
zoonotic risk from suspected/confirmed cases salmonellosis, so it
is essential that strict personal hygiene methods are used during
and afterhandling sick sheep:
Minimise the number of
people with contact with such sheep.
Remove and disinfect outer
clothing after handling.
Wash and clean thoroughly
hands, arms and face after handling
Under veterinary advice,
whole group long-acting oxytetracycline injections (20 mg/kg ) may
reduce the number of abortions during an outbreak of salmonellosis
in sheep but this is an emergency procedure only and all other
means of prevention must be adopted. Antibiotic use on farm must
only be used when all other means of prevention have been