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Monday, 11 May 2015

Abortion in Ewes
Infectious causes of abortion are most common after day 100 of pregnancy. When abortion rates are above 2% it is likely that an infectious cause is to blame, whereas in sporadic cases the cause is usually down to handling procedures or movement. Enzootic abortion of ewes is attributed to Toxoplasma gondii and Campylobacter species causing over 70% of abortion outbreaks in the UK. The cost of abortion is variably quoted as between £20 and £65 per ewe.

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 should never be dismissed.

Biosecurity-
reduce/prevent the introduction of new diseases onto your farm from outside sources.

Biocontainment
- reduce/prevent the movement of infectious diseases on your farm. In keeping with most procedures for infectious diseases, sheep that have suffered from infectious abortion should be isolated from the main flock and all abortion material disposed of correctly. Any ewe lambs fostered on to aborted ewes should not be retained for breeding in future. The potential for zoonotic transfer should be stressed to all persons in contact with any aborted ewes or abortion material.


Diagnosis Requirements:
the minimum articles needed for laboratory submission for abortion include… foetus(s) or foetal stomach contents, a piece of placenta and a maternal serum sample collected by veterinary surgeon. While one submission may identify an infective agent it is important to look for other infective agents in other cases.

Common Causes of Abortion
Enzootic abortion of ewes, Toxoplasma gondii and Campylobacter species cause over 70% of abortion outbreaks in the UK.

Chlamydial Abortion / Enzootic Abortion of Ewes (EAE):
Pregnant women are at serious risk from C. abortus infection. The infective agent is a bacteria, Chlamydophila abortus. Despite a widely available and highly efficacious vaccine, EAE is still the main cause of ovine abortion in the UK. The disease is transmitted by ingestion following exposure of susceptible sheep to high levels of infected uterine discharges and aborted material. Infection does not result in abortion in pregnancies where the ewe is less than 6 weeks away from lambing; rather, the infection remains latent in that ewe until further seasons and then causes abortion.
Infection typically results in the abortion/birth of the fresh/dead and/or weak lambs during the last 3 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 possibly a drawn up abdomen. Live lambs rarely survive more than a few hours despite supportive care.
Whole flock long-acting Oxytetracycline injection (20mg/kg) may reduce the number of abortions but such treatment cannot reverse placental damage and often lambs will still be born weak and will consequently die soon after birth. While this does not save lambs at risk, it does allow ewes to hold lambs closer to term, therefore become available to foster lambs (only male) at a closer time to their own natural lambing; this means they are more likely to be carrying sufficient milk to take on an orphan lamb.

Toxoplasmosis
*People with an immunosuppressive illness are at risk of illness. Infection of susceptible women during pregnancy can result in infection of the baby which may cause serious eye and brain damage*
This disease results from infection of susceptible sheep with protozoan parasite (Toxoplasma gondii). The sexual cycle takes place in cats while the asexual cycle can occur in range of species including sheep.
Toxoplasma infection during early pregnancy may be manifest as embryo/early foetal loss with an increased number of returns to service after an irregular extended interval or an increased barren rate, often above 8-10%. 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 mummified foetus. The foetus has a dark brown leathery appearance and is about 10cm long.
Diagnosis is usually based on identification of specific changes in the placenta in combination with the detection of high levels of antibodies in ewe blood. Antibody may also be present in the foetal fluids and can also be detected in new born lambs before they have sucked colostrum. Blood sampling is not sufficient on its own as it only shows that the ewe has been infected with the parasite; it does not show the current cause of the abortion.
Prevention/Control: minimal contact from cats is promoted. Vaccination provides excellent immunity to natural infection and should be administered at least 3 weeks before breeding season. Care should be taken when administering the vaccine. The vaccine costs £3 per dose, but does provide life-long immunity.

Campylobacteriosis
Campylobacter fetus and Campylobacter jejuni are common cause 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 or pasture whenever possible. By the time the abortions are recognised, the infection has already spread through a large proportion of the flock so treatment options are limited.
During late gestation the flock should be managed in an environment as clean as possible. 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.





Salmonella Abortion
Salmonella Montevideo, -Dublin and –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. If possible, feed should be kept safe from vermin. Water sources 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 significant zoonotic risk from suspected/confirmed cases of salmonellosis so it is essential that strict personal hygiene methods are implemented.
Whole group long-acting Oxytetracycline injections (20mg/kg) may reduce the number of abortions during an outbreak of salmonellosis in sheep.

SUMMARY
  • Many infectious causes of abortion can also infect humans (zoonotic infection)
  • An abortion rate in excess of two per cent is suggestive of an infectious cause and veterinary investigation is essential
  • All aborted ewes must be isolated immediately
  • Aborted material and infected bedding must be removed and destroyed to prevent spread of disease on your farm
  • Maintain a closed flock wherever possible
  • Purchased all flock replacements as maiden sheep whether ewe lambs or gimmers
  • Never buy old pregnant ewes - they are seldom a bargain and always a great disease risk
  • The cost of abortion is ranges from £20 to £65 per aborted ewe
  • Vaccinate all flock replacements against EAE and Toxoplasmosis (costs around £1 per pregnancy)
  • All feed must be stored in vermin-proof bins
  • Sheep should be managed in clean environments
  • 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.


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