Abortion diseases often remain hidden until significant losses occur
Report Shows Abortion Vaccines Could Save £8000 Per 100 Ewes In A Flock
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Sheep farmers could prevent annual losses by up to £8,430 in a 100-ewe flock by vaccinating against common sheep abortion pathogens, according to new research1.
A report by veterinary surgeon Dr Laura Worsley¹, made possible through the MSD Animal Health research bursary scheme, examined the financial impact of vaccination programmes in flocks affected by enzootic abortion of ewes (EAE) or toxoplasmosis, and in naïve flocks.
Using partial budget analysis to assess a range of flock scenarios, the study found that vaccination delivered a clear financial benefit in every case evaluated.
For a 100-ewe flock, the average annual increase in net revenue was £1,932 and £2,514 for EAE and toxoplasmosis, respectively, where flocks were already infected and the diseases were endemic¹. However, the greatest gains were seen in naïve flocks, where vaccination acts as insurance against a potential abortion storm. In these cases, the research showed that annual savings of £5,640 for EAE and £8,430 for toxoplasmosis could be made when considering the losses that would reasonably be expected following an initial flock breakdown1.
The modelling was designed to reflect a wide range of GB flock systems, making the findings applicable across different management, husbandry and biosecurity practices.
Dr Worsley, who previously worked in clinical farm practice, says the upfront cost of vaccination is often what discourages uptake.
“The headline cost can put farmers off,” she explains. “But what this study clearly demonstrated is that across more than 10,000 modelled outcomes, vaccination never resulted in a financial loss, even when lower lamb prices were factored into the calculations. Every scenario showed a positive return1.”
She believes timing also influences decision-making. Abortion vaccines must be administered prior to tupping, months before lambing, when abortion losses are not front of mind and the following season’s lamb price is still unknown.
“Farmers are making that decision at the point furthest away from seeing the consequences,” she says. “But the modelling shows that regardless of lamb sale price, vaccination remains financially beneficial.”
While lamb price had the greatest influence on the financial model1, meaning pedigree and high-value flocks stand to gain the most, abortion rate, neonatal mortality and barren ewe rates (in toxoplasmosis-affected flocks) also significantly affected returns. Farms already experiencing higher losses in endemic scenarios saw the strongest financial improvement from vaccinating.
Dr Worsley stresses that the true cost of abortion disease goes beyond the obvious loss of lambs.
“It’s not just the abortion that needs costing in,” she says. “Barren ewes carried through the season or higher replacement ewe costs (depending on a farmer’s culling policy for aborted ewes), weaker lambs, labour, diagnostics and higher neonatal mortality all add up. When you look at the full picture, the economic impact is much greater than many farmers realise.”
And national data highlights the risk posed to farms, with the Animal and Plant Health Agency (APHA) identifying enzootic abortion and toxoplasmosis as the two most common causes of sheep abortion in Great Britain2.
Despite this, the Agriculture and Horticulture Development Board (AHDB) has reported only about half of flocks vaccinate against enzootic abortion3, while uptake for toxoplasmosis remains lower at just 26% in 20243, suggesting considerable scope for wider protection.
Further insight from the subsidised FlockCheck programme run by MSD Animal Health4 found that among 400 flocks tested last year, 79% had been exposed to Toxoplasma gondii and 35% to Chlamydia abortus, the bacterium responsible for enzootic abortion.
MSD veterinary adviser Dr Kat Baxter-Smith warns that abortion diseases often remain hidden until significant losses occur.
“Once established, they are extremely difficult and costly to manage, making prevention through vaccination vital,” she says. “Given the high exposure levels across GB flocks, vaccination should form a core part of flock health planning, particularly for replacement ewes.”
Enzootic abortion is highly contagious, with infected ewes frequently showing no signs until late pregnancy, and some becoming lifetime carriers. Toxoplasmosis commonly results in early embryo loss, barren ewes and weak lambs, with infection typically occurring via pasture, feed or water contaminated by cat faeces.
With margins under continued pressure, the research1 suggests that preventing abortion losses may be one of the most straightforward and consistent ways to safeguard flock productivity and profitability.
Farmers are encouraged to discuss testing for abortion and low barren rates, as well as vaccination plans, with their vet to help safeguard their flock, with the subsidised 2026 FlockCheck scheme, available through veterinary practices until 30 June 2026.
References
- Worsley, L. Investigating the Financial Impact of Implementing Vaccination Programmes for Enzootic Abortion of Ewes and Toxoplasmosis Infection Using Partial Budget Analysis. MSD Animal Health Research Bursary Report
- K. Baxter-Smith, E. Thornley, O-073 Seroprevalence of enzootic abortion and toxoplasmosis in sheep flocks experiencing reproductive losses, Animal - science proceedings, Volume 14, Issue 1,2023.
- Pages 109-110,2025 AHDB Vaccine Uptake Report for Cattle and Sheep Vaccine uptake report for cattle and sheep | AHDB
- MSD 2025 FlockCheck results from 400 farms.
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