The Department of Primary Industries and Regional Development (DPIRD) investigates cases of infertility or abortion in sheep every year in order to support Australia's export markets by testing for and ruling out trade-sensitive exotic diseases such as enzootic abortion of ewes, caused by Chlamydophilia abortus, and Salmonella abortus. Investigating abortion and infertility may also show a zoonotic disease (one that can infect people) is causing the problem, which is important so that farmers can take steps to protect their health.
There are multiple possible causes of both infertility and abortion, but making a definitive diagnosis is often difficult 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)
Causes of infertility include ram and ewe factors. Selected issues are discussed below.
Brucella ovis infection results in epididiymitis and reduced sperm production
Prevention: 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.
Several infections including Corynebacterium pseudotuberculosis (cheesy gland), Actinobacillus seminis and Histophilus somni can cause abscesses or inflammation that decrease sperm production.
Prevention: Rams should be vaccinated against cheesy gland and checked for testicular disease (see B. ovis above).
Fever/increase in body temperature
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 maturition 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 - overconditioned 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.
Prevention: 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.
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. See Ovine brucellosis for more information.
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 at joining is strongly linked to flock fertility, ewe condition at lambing and lamb and dam survival. More than 85% of the ewe flock should be in body condition score 3 or higher at joining to maximise flock fertility.
For more on management processes and disease management during the joining period see Joining – setting the potential of your ewe flock.
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 by a vet. 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, when low marking percentages are noticed. Monitoring of the flock for evidence of abortion allows early detection and the best chance of obtaining diagnostic samples. A confirmed diagnosis allows cost-effective intervention and best advice on avoiding the problem in subsequent seasons.
Infectious causes of abortion
Reportable diseases (diseases exotic to Australia)
It is important to Australian sheep export markets to be able to demonstrate continued freedom from enzootic abortion and exotic brucellosis and salmonellosis. Investigating abortion storms in sheep can provide this evidence and increases trading partner confidence in our claims of freedom from these significant diseases of sheep.
Enzootic abortion of ewes, caused by Chlamydophilia abortus, is exotic to Australia. This infection causes abortions in the last couple of weeks of pregnancy, stillbirths, weak lambs and a persistent vaginal discharge. It is also a zoonosis (can infect people).
Brucella melitensis is exotic to Australia. It causes abortion storms in the second half of pregnancy when first introduced to a flock. Abortions are generally followed by a vaginal discharge. B. melintensis is zoonotic.
Samonella abortus is also exotic to Australia. It causes abortions in mid to late pregnancy, stillbirths, weak lambs and fever associated with metritis and peritonitis in ewes.
All of the following disease occur in Australia and are zoonotic.
- Causes late abortions and stillbirths. The source of the infection is feed or pastures contaminated by cysts shed in the faeces of infected cats. There is no effective treatment.
- Causes abortions 5-6 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 and excrete it in their faeces but the most common source of the infection is damp or spoiled feed, especially hay or poorly prepared silage.
- Causes outbreaks of acute disease characterised by blood in the animals' urine, jaundice, and death (usually in lambs), and abortions. It may also cause stillbirths and weak lambs.
- Causes abortions. Few other clinical signs are seen in infected sheep.
Since a number of diseases which cause abortions in sheep are zoonoses, all producers handling lambing and aborting ewes should observe hygiene precautions. Always wash hands with soap or detergent after handling aborted material and affected ewes. Producers working with sheep should discuss Q fever and leptospirosis vaccination with their doctor. Toxoplasmosis and listeriosis are particularly a concern for pregnant women. Pregnant women should avoid handling aborting ewes where possible until a diagnosis is made.
Other endemic infections
Infection causes late abortions and weak or stillborn lambs. Campylobacter survives in the digestive system of some sheep and cattle and is shed onto pasture. Once a flock is infected the majority of the flock develops immunity. There is a vaccine for Campylobacter available in Australia.
Salmonella typhimurium causes abortion due to the high fever associated with infection. During an outbreak other clinical signs include diarrhoea with blood and ewe deaths. Salmonella infections are more common in confined, high stocking density such as feedlots or when stock are drinking from dams contaminated by sheep faeces after heavy rain.
Border disease (pestivirus) also known as hairy shaker disease
Infection causes abortions when the ewe is infected in early pregnancy. In later pregnancy it can cause undersized lambs, stillbirths, and abnormal fleece, skeletal abnormalities, and nervous signs in surviving lambs. Clinical signs of border disease will only been seen when virus is first introduced to the flock, normally by an introduced sheep that is persistently infected.
Infection causes mid- to late-term abortions. It can also cause weak full-term lambs and nervous signs. Abortions due to Neospora are more common in cattle than sheep. Neospora caninum can be introduced to a flock through dog faecal contamination of feed sources.
Non-infectious causes of abortion can include:
- trace element deficiencies: copper, selenium
- toxins including annual ryegrass toxicity (ARGT).
Producers with ewe infertility or abortion issues should:
- call a vet to undertake an investigation - see below for information about subsidised testing
- consider other recommendations for maximising lambing percentage through nutrition and management (Lifetime Wool/Meat and Livestock Australia – flock size, lambing condition, nutrition, shelter).
Targeted surveillance of ewe abortions and lamb deaths
The Department of Primary Industries and Regional Development conducts a surveillance program for ewe abortion and newborn lamb deaths to assist sheep producers to identify the cause of abortions and newborn lamb losses in their flocks.
The program provides important surveillance and testing to support WA’s sheep markets.
More information is available at: Ewe abortion and newborn lamb deaths surveillance program
If you see unusual disease signs in your stock, call your private vet, a DPIRD vet, or the Emergency Animal Disease hotline on 1800 675 888.