Ovine Observer

Infertility and abortion in ewes

Anna Erickson
Department of Agriculture and Food, Western Australia – Narrogin
Email: anna.erickson@agric.wa.gov.au

DAFWA’s Animal Health Labs investigate infertility or abortion in sheep every year. There are multiple possible causes of both infertility and abortion, but making a definitive diagnosis is often very difficult. This is for several reasons:

• Testing is often retrospective. Diagnosis of infertility is often only made at scanning while the cause of the problem was earlier, at joining. Similarly, investigation of foetal loss, abortion or early lamb deaths may only be instigated at marking.
• Incomplete sample sets are often submitted. For extensive testing a wide set of samples is required. This includes blood from both the ewe and her flock mates, vaginal swabs, and samples from the placenta and aborted foetus. These last two are often not available.
• A number of non-infectious factors can cause infertility including nutrition, trace element deficiencies, management problems and severe weather events.

It is important to distinguish between infertility and abortion. Causes of infertility (failure to conceive) include ram and ewe factors. Selected issues are discussed below.

Ram factors:

• Brucella ovis infection results in epididymitis and reduced sperm production. Producers should buy rams only from B.ovis accredited flocks, and run young rams separately from older or suspect rams in the off season. Maintain good boundary fences to keep out strays. Check all rams for any signs of testicular and epididymal disease before joining and cull any suspect animals.
• Testicular inflammation. Several infections including Corynebacterium pseudotuberculosis (cheesy gland), Actinobacillus seminis and Histophilus somni can cause abscesses or inflammation that decrease sperm production. Rams should be vaccinated against cheesy gland and checked for testicular disease (see B.ovis above).
• Any condition which causes a fever or rise in body temperature can damage sperm. As sperm production takes at least six weeks, infertility will continue until maturation of new healthy sperm. Temporary infertility can result from: 
  • Shearing – increased susceptibility to heat stress during the summer, as well as infection of shearing cuts.
  • Dipping – apart from infection, dips may produce fever for a short period.
  • Droving – fast droving in hot weather can cause a significant rise in body temperature. Many breeders prefer to deliver the rams to the joining paddock by truck.
  • Flystrike – flystrike is invariably associated with fever. It is good practice to jet the polls of rams prior to joining.
  • Over-fat rams – over conditioned rams are more likely to be affected by hot weather and droving, and can get a high temperature when going straight into work.
  • Some drugs can suppress sperm production. Always check with a vet before giving medications.

All management procedures such as shearing and dipping should be done well ahead of joining. The six week sperm production period should also be considered in other aspects of pre-joining ram management, including for supplementary feeding and examination.

Ewe factors:

• Brucella ovis. Ewes infected with B.ovis at mating usually abort at a very early stage and return to oestrus. They are a source of the infection for rams during this time. Most ewes will not remain infected for more than two oestrus cycles but this can cause a prolonged lambing period. For those using a very short joining period it can result in very low pregnancy rates.
• Clover disease. Sheep grazing pastures with more than 30% of Trifolium species clovers early in the growing season may show reduced conception rates. Mature pastures are less risky.
• Ewe condition. Ewe condition at joining is strongly linked to flock fertility, ewe condition at lambing and lamb and dam survival. Greater than 85% of the ewe flock should be in BCS 3 or higher at joining to maximise flock fertility.

Abortion is defined as the termination of a pregnancy. It is normal for 1.5–2% of ewes to abort in any one year, but abortion ‘storms’ with rates above 5% should be investigated. These can occur at any stage of the pregnancy but later term abortions are more often noticed. Even in later abortions, scavengers will often remove the foetus and afterbirth before producers notice it, so an issue with abortions may only be diagnosed retrospectively. Monitoring of the flock for evidence of abortion allows early detection and the best chance of obtaining diagnostic samples. A firm diagnosis allows implementation of the most cost effective intervention and best advice on avoiding the problem in subsequent seasons.

Infectious causes of abortion include:

• Toxoplasmosis. This causes late abortions and stillbirths. The source of the infection is feed or pastures contaminated by cysts and shed in the faeces of infected cats. There is no effective treatment. Control mainly consists of controlling feral and domestic cats’ access to sheds used to store sheep feed. During an outbreak, prompt removal of any aborted material may help reduce the extent of the outbreak.
• Listeriosis. This causes abortions five to six weeks before the expected date of lambing. It can also cause stillbirths and increased death rates in the first few days after birth. Abortion rates can be up to 20%. Some apparently healthy animals carry Listeria but the most common source of the infection is damp or spoiled feed, especially hay or poorly prepared silage.
• Campylobacter infection. This causes late abortions and weak or stillborn lambs. Campylobacter survives in the digestive system of some sheep and cattle and is shed onto pasture. Antibiotics may help reduce the extent of an abortion storm due to Campylobacter, along with hygiene and prompt removal of any aborted material. There is a vaccine available for Campylobacter in sheep which may be useful in protecting naïve flocks (flocks where the infection is not currently present, based on blood test results) or when introducing maiden ewes into a flock where infection is known to be present. However, independent advice should always be sought from a veterinary surgeon before starting a vaccination programme.
• Other infectious causes of ewe abortion include Q fever (Coxiella burnetti), leptospirosis, opportunistic bacterial infections and the Akabane and Border disease viruses.
• Non-infectious causes of abortion may include ergotism, metabolic disorders and nutritional deficiencies. 

Several of the above infections are zoonoses, that is, they can cause disease in people. All producers should exercise extra hygiene when handling ewes that have aborted or the aborted material itself, including wearing gloves and washing hands and tools in soap or detergent. Toxoplasmosis and listeriosis are particularly a concern for pregnant women. Pregnant women should avoid handling aborting ewes until a diagnosis is made.

Enzootic abortion of ewes, caused by Chlamydophilia abortus, is exotic to Australia. This infection causes abortions, systemic illness with fever, and stillbirths. It is also a zoonosis. It is important to our export markets to be able to demonstrate continued freedom from enzootic abortion and therefore abortion storms in sheep should always be investigated.

Recently, sheep exports were disrupted by blood samples testing positive for Chlamydophilia abortus. These appear to be false positives, but sheep which test positive are excluded from export consignments. The exact reason for false positives is not clear but there may be cross reactions occurring with another strain of the bacteria, C pecorum, which is present in Australia and can cause pink eye, arthritis and pneumonia.

Producers with infertility or abortion should:

• undertake a thorough investigation of all likely causes before trusting one intervention to solve the issue
• consider other recommendations for maximising lambing percentage (Lifetime Wool/MLA – flock size, lambing condition, nutrition, shelter).

If you notice abortions in your sheep, or find your stock unexpectedly sick or dead, the Subsidised Disease Investigation Pilot Program can help you get the issue fully investigated by a veterinarian at reduced cost. The pilot program, funded by Royalties for Regions, subsidises the cost of full investigations into stock deaths or disease to increase surveillance and testing for exotic animal diseases in WA.

This testing supports the WA livestock industry but the added benefit is that, for reduced cost, you can find out the cause of the disease on your farm. This gives you the opportunity to put control measures in place to minimise losses. Contact your private or DAFWA veterinarian to request a subsidised disease investigation.