printStock Journal Technical Article: May 2026
Author: Jim Walsh, Coopers Animal Health
With lambing underway or approaching on many properties, now is an ideal time to review results and plan monitoring. Assessment of lambing outcomes helps determine how well management practices and interventions were delivered, and highlights opportunities to improve next season’s results.
Monitoring during pregnancy and lambing may include lamb post-mortems to assess signs of mismothering or dystocia, and veterinary investigations into abortion causes. Pregnancy scanning and lambing results should also be reviewed carefully to identify any contributing factors behind suboptimal performance.
Several key areas influence lambing success and foetal survival. These include ram health, condition and management, including the 5 Ts, joining percentage, length of joining, ram age and paddock management. Ewe condition score and nutrition at joining and throughout pregnancy are also critical. Pregnancy scanning to identify of single- and multiple- bearing ewes allows the best allocation of nutrition. Lambing mob size and lambing paddock management are important, as are animal health treatments and paddock preparation.
A useful place to start is by comparing pregnancy scanning results with marking results. Is there a large difference between the two? Are maiden ewes significantly behind older ewes? A difference of around 20% may indicate an issue worth investigating.
The best diagnosis of foetal loss comes from veterinary post-mortem examination and laboratory testing of the foetus and/or placenta. Early abortions or foetal resorptions are often missed, and aborting ewes may show no obvious signs of illness before recovering.
Potential causes of abortion include stress, such as extreme heat, transport stress or unusual handling such as shearing. Toxins, including plant and environmental toxins, should also be considered. Infectious abortion should be suspected when no other clear cause is found.
Common infectious causes include Campylobacteriosis (vibriosis), toxoplasmosis and listeriosis. Less common causes include brucellosis, leptospirosis, salmonellosis, Border disease and chlamydia. Blood tests can detect exposure to some infectious agents, but testing should be targeted at sheep that have lost lambs after scanning.
Campylobacter fetus fetus is considered the most common cause of infectious abortion in Australian sheep. Healthy carrier ewes can shed the bacteria in faeces, contaminating feed and water. Infection can then spread to pregnant ewes, with bacteria reaching the placenta and foetus and causing abortion.
Aborted materials, including the placenta, fluids and foetus, are highly infectious and can increase exposure to other animals in the mob. C. fetus may persist in uterine discharge for up to six weeks. In severe cases, this can lead to an abortion storm, with 40–50% of ewes affected.
Abortions or resorptions may be detected at scanning, while infection can also show up later as premature lambs, stillborn full-term lambs, weak lambs or lambs that die within a few days of birth. Maiden ewes, particularly ewe lambs, are often naïve to Campylobacter. Foetal losses in these groups are commonly low-level and endemic, with average losses over time estimated at 9–12%. Older ewes may also become high-risk, even after previous exposure or vaccination, if immunity is overwhelmed.
High stocking rates, trail feeding, containment feeding and cell grazing during pregnancy can increase faecal exposure. Stress and nutritional challenges may also reduce immune response. In high-risk flocks, vaccination with Campyvax prior to joining, or early in joining, is strongly recommended to help minimise losses.