Sheep Abortion in Ewes

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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 70 per cent of abortion outbreaks in the UK. The cost of abortion is variably quoted as £20 to £65 per aborted ewe.

General principles - Biosecurity and Biocontainment
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 £20 to £65


Fig 2: The most common causes of abortion are readily prevented by vaccination
Biosecurity
Reduce/prevent the introduction of new diseases onto your farm from outside sources.

Freedom from most infectious causes of abortion is best achieved by maintaining a closed clean flock.

Biocontainment
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 footwear.

Diagnosis of the cause(s) of abortion
The minimum requirement for laboratory submissions for abortion diagnosis include 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 2010
COMMON CAUSES OF ABORTION

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.



Fig 8: Sheep grazing a field where run-off from a cattle midden has collected posing a significant threat
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 mummified fetus. The mummified fetus has a dark brown leathery appearance and is about 10 cm long



Fig 9: Seabirds can be a significant source of certain Salmonella species - feed on a clean area of the field every day
Diagnosis


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

Management/Prevention/Control measures

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 pregnancy.

Salmonella Abortion
Salmonella 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. 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
Whole group long-acting oxytetracycline injections (20 mg/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.
NADIS hopes that you have found the information in the bulletin useful. Now test your knowledge by enrolling and trying the quiz. You will receive an animal health certificate for this subject if you attain the required standard.

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