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Barrenness or abortion in sheep flocks earlier this year was likely caused by an insidious disease such as toxoplasmosis, according diagnostic results analysed by... Blood tests highlight need for pre-tupping vaccination

Barrenness or abortion in sheep flocks earlier this year was likely caused by an insidious disease such as toxoplasmosis, according diagnostic results analysed by MSD Animal Health.

Blood samples from sheep farms were tested when the subsidised FlockCheck diagnostic service was made available to vets in practice between February 2021 and June 2021.

Data from 375 UK sheep farms suggest two-thirds of flocks had one or more ewes testing positive for the Toxoplasma gondii parasite, which causes toxoplasmosis, said MSD animal health livestock veterinary adviser Kat Baxter-Smith.

The continued high national level of exposure of UK sheep to Toxoplasma gondii highlights the importance of vaccinating ewes against what is a productivity-damaging parasite, said Dr Baxter-Smith.

“We consistently see about two-thirds of UK sheep units testing positive for this serious, productivity-limiting parasite. Consequently, we urge all sheep producers to discuss their farm situation with their vet.”

Toxoplasmosis also causes reabsorptions, mummified fetuses, stillbirths and weakly lambs ­– as well as barrenness and abortions. But its impact on flock profits is often significantly underestimated.

“The industry focus should be on preventing infection in breeding ewes and the best way to do that is to vaccinate replacements well before they go to the ram. The clear industry advice is to ensure every ewe is vaccinated before she breeds.”

Normal biosecurity measures are not enough to control the disease, said Dr Baxter-Smith. Infected cats were one way the parasite spread to sheep, shedding toxoplasma eggs in their faeces which were then ingested by sheep on contaminated pasture.

Sheep producers who recorded a flock barren rate greater than 2% during the 2021 lambing season should talk to their vet for advice well before tupping this year, even if diagnostic blood samples had not been taken.

Dr Baxter-Smith said the Toxovax toxoplasmosis vaccine was known to protect ewes for at least two lambing seasons and could be given to breeding females at any time between four months and four weeks before tupping.

Another underlying disease problem that often manifests itself as significant early lamb losses is enzootic abortion (EAE). This disease can cause devastating abortion storms affecting approximately 30% of ewes.

“Once a flock has the disease it is likely it will never disappear due to its persistence in carrier sheep. The disease often arrives on farm through bought-in replacements and is passed on from ewe to ewe at lambing.”

An infected unvaccinated ewe would more than likely abort, said Dr Baxter-Smith. But the Enzovax vaccine could protect ewes for at least three years.