Pregnancy Diagnostics in Ewes

Yesterday, I had the opportunity to assist with pregnancy diagnostics on 80 ewes. My previous experience has primarily been with cattle, where trans-rectal ultrasound is commonly used to identify a fetus. In contrast, sheep are typically scanned using a trans-abdominal ultrasound approach to determine pregnancy status (Figure 1).

On this farm, the ewes had been exposed to two rams for approximately 60 days. This timing placed most of them in the 60–90 day window of gestation, a period when fetuses are generally easy to visualize. However, as we progressed through the herd, we were only able to identify 4 pregnancies out of 80 ewes—a concerningly low rate.

Given the poor conception rate, the veterinarian and I began to consider possible infectious causes. One likely suspect was enzootic abortion of ewes (EAE), caused by Chlamydia abortus. This pathogen is highly contagious and can be spread through contaminated fetal membranes and placentas. It is easily transmitted between ewes and may also be spread by rams through mating.

To investigate further, we collected blood samples from both pregnant and non-pregnant ewes to submit for a reproductive disease panel. This panel will test for common infectious causes of reproductive failure, including chlamydia and toxoplasmosis.

Our working hypothesis is that Chlamydia abortus may be circulating within the herd. While it would be preferable for the disease to be introduced and spread primarily through the rams (which are fewer and easier to manage), it is more likely that horizontal transmission is occurring among the ewes.

Depending on the results of the diagnostic tests, the producer will have to decide on an appropriate management strategy. Options may include treatment with antibiotics, implementation of vaccination protocols, or more drastic measures such as culling the affected animals and rebuilding the flock with replacement stock.