If an abortion occurs late in pregnancy dead lambs will likely be seen in the paddock. Earlier in pregnancy, the fetus may be reabsorbed with no obvious sign of pregnancy loss. These are more likely to go unnoticed until a high number of dry ewes are found after lambing.


A ‘normal’ lamb loss rate of 1-2% from scanning to birth is reported on most sheep farms in New Zealand. However, an ‘abortion storm’ can result in 25-40% of ewes aborting in a single flock. In any one year 3-5% of sheep farms will experience an abortion storm. Diagnosis of the cause of an abortion storm usually requires lab testing.sheep and lamb

Campylobacter

Campylobacter is a bacterial disease and is one of the most common causes of abortion diagnosed in New Zealand. Ewes of any age or breed can be affected by Campylobacter and the disease has been reported in most areas of the world where sheep are farmed. Abortions generally occur in the last three months of pregnancy. To confirm diagnosis call your vet to discuss your situation and have samples sent to a laboratory for testing.

In a typical Campylobacter outbreak one or two ewes abort around 3-4 months into pregnancy and this is followed by a spike in abortions or an abortion storm 2-3 weeks later. Infection can spread very quickly within a flock by contact with aborted lambs, after-birth or birth fluid. The time between infection and abortion can range from 13 to 113 days but is often within a month.

Campylobacter can be found in vaginal discharge for up to six weeks after abortion. However, some animals will become carriers and maintain the bacteria in their gut. They will usually look completely healthy and may be present on farm or arrive with recently purchased ewes.

Campylobacter abortion storms can be prevented with vaccination. We recommend Campyvax 4. Maiden ewes should be vaccinated twice, 4 -8 weeks apart, prior to tupping with a booster vaccination given yearly prior to tupping. Contact your local Franklin Vets team to discuss the timing of vaccination in your flock and ordering your vaccine.

Toxoplasmosis

Toxoplasmosis is the second most commonly diagnosed cause of abortion in sheep in New Zealand. Toxoplasma is a small parasite that has a complicated lifecycle and problems in sheep arise when susceptible ewes become infected during pregnancy.

Ewes are infected when they eat pasture or hay contaminated with cat faeces containing Toxoplasma oocysts (the egg-like stage). When cats are infected they will shed millions of Toxoplasma oocysts in their faeces and these eggs survive in the environment incredibly well, becoming a source of infection for sheep for many years. The timing of infection determines what is seen by the farmer.

  • Not pregnant – no visible signs of infection. Immunity is likely to develop.
  • Early pregnancy – the foetus is reabsorbed and there are no visible signs that pregnancy has been lost.
  • Mid-pregnancy – abortion, dead, possibly mummified, lambs may be found in the paddock.
  • Late pregnancy – stillborn lambs or weak lambs that die shortly after birth or fail to thrive.

Ewes that have been infected with Toxoplasmosis will be infected for life but will develop ‘immunity’ and generally will not have Toxoplasma abortions in the future.

Controlling feral cats on farm is an important part of preventing Toxoplasma abortions in ewes. This is also important as Toxplasma can cause illness in people, particularly children and pregnant women. However, because feral cats can be very difficult to control and because the oocysts last a very long time, vaccination needs to be a crucial part of your control plan. Toxovax is the only vaccination available to prevent Toxoplasma abortions in sheep. You only need to give one shot for life, but vaccination needs to be given at least one month before the start of mating. You will also need to pre-order Toxovax as it is only made to order and has a very short shelf life once it is made. Contact your Franklin Vets team to discuss ordering Toxovax for your flock.

Other Causes of Abortion in Sheep

Salmonella Brandenburg is known to cause sheep abortions mostly in the eastern and southern parts of the South Island. It is a bacterial disease that can also result in severe illness or death in ewes. Vaccination is available.

Hairy Shaker Disease is a viral cause of abortion which is again more common in the South Island. There is no vaccine available, but control can be achieved through appropriate management.
Listeria and fungal abortions are usually associated with feeding poor quality or mouldy silage. Silage that has spoiled is not an appropriate feed source for pregnant stock.

Abortion outbreaks in sheep should be investigated as soon as possible by your vet give the best chance of an accurate diagnosis and control plan. If you are concerned about abortions in your sheep flock, contact your Franklin Vets Clinic to discuss the best way forward for your farm.