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Avoiding losses between scanning and lambing make a big impact on live lamb numbers. Abortion can be attributed to a few causes and protection from EAE and Toxoplasmosis is essential, we discuss causes, treatment and some useful vaccinator tips and suggestions. Get the facts and protect your flock.
Abortion prevention in breeding flocks Most sheep flocks experience a few sporadic losses in late pregnancy which can be attributed to high stress situations. Ensuring staff know the correct handling procedure and adequate feeding trough space can mitigate this risk somewhat. This does not explain however higher losses that can occur and a recent study observed one third of losses between scanning and lambing1. They have been attributed to a more sinister cause of abortion. At worst this can be an abortion storm2 affecting a largely clean and uninfected flock and veterinary investigation is essential as soon as possible to save as many lambs as possible3.
The three main infectious causes of abortion observed and recorded by AHDB4 over the last five years, are:
Enzootic abortion of ewes (EAE) caused by Chlamydia abortus
Toxoplasmosis
Campylobacter spp.
The epidemiology of these three infections is very different, any one of them can cause outbreaks of abortion in flocks. In an outbreak, up to 40% of ewes may either abort or produce weak, poorly viable lambs estimated at a cost of between £11–48m per year in 20055 for enzootic abortion alone to the UK flock.
Enzootic abortion (EAE) EAE is caused by a bacteria-type organism called Chlamydophila abortus and usually arrives on farm from bought in breeding replacements. Wildlife can also carry infected placentae. EAE is passed on infected afterbirth from ewe to ewe, on new lambs and in vaginal discharges which can occur for up to two weeks post-lambing. Lambs can also be born already infected6. If there is EAE on farm therefore, there is also a risk of breeding replacements becoming carriers too.
The Chlamydophila abortus spreads to the womb and afterbirth fluids of an unprotected ewe and kills the developing lambs. The signs of EAE however, may not show in newly infected animals during that same lambing season and there is no test to reveal them. This dormancy breaks approximately three weeks before the next lambing the placenta becomes inflamed and abortion in the ewe occurs.
Toxoplasmosis
Toxoplasma eggs are most commonly spread by cat faeces after ingesting rodents infected by Toxoplasma cysts. Eggs can survive on-farm for over a year. Toxoplasma is not commonly passed from sheep to sheep but exposure is almost 100%7.
Losses from Toxoplasmosis occur both during and after pregnancy with reabsorptions in early pregnancy abortions later on, mummified fetuses, stillbirths and weak live lambs. Barrenness and impacts on flock fertility.
Campylobacteriosis
Campylobacter is a bacterial infection often observed in highly intensive flocks in unhygienic environments during late gestation. Bought in sheep are often the source of infection. Abortion in late gestation or weakly lambs whom often die are typical outcomes.
Good hygiene practices around feeding areas and managing any bought in animals separately can lessen the risks. After any infection, ewes are immune to a further challenge and will not abort.
Salmonella Abortion
Various Salmonella strains including; Salmonella Montevideo, Salmonella Dublin and Salmonella Typhimurium have been linked with abortion and death in pregnant ewes8. Sheep may simply be found dead with rotten lambs in the womb. Infection routes include contaminated feedstuffs and water courses, sewage effluent overflow, carrier cattle, and carrion. Feed should be in vermin-proof bins but this is rarely achieved on many farms. Feed troughs should be tipped and moved after feeding. Trailed Snackers need to be used on clean ground each day to minimize risk. Water ideally should be mains supplied.
Abortion management
Isolate aborted ewes need to be immediately separated as they can spread disease for some time after aborting. They need to be marked or EID numbers recorded for future blood sampling or culling. All bedding etc. should be burned and pens thoroughly disinfected.
Aborted lambs need to be collected together with all afterbirth material and submit via the local vet to the regional veterinary laboratory for diagnosis. A number of fresh samples may need to be sent to ensure a definitive diagnosis.
Avoid fostering ewe lambs onto aborted ewes who may be kept as replacements as a strong chance of infection and possible abortion issues when they join the breeding flock.
The use of antibiotics to control enzootic abortion is not considered best practice responsible use.
Table 1 Main vaccination options
Effective vaccines available against EAE & toxoplasmosis; Source AHDB | Enzovax | Live vaccine for the active immunisation of breeding female sheep against C. abortus infection |
| Cevac® Chlamydia | Live vaccine for the active immunisation of breeding female sheep against C. abortus infection |
| Inmeva Suspension | Inactivated vaccine for the active immunisation of breeding female sheep against C. abortus infection and Salmonella enterica subsp. enterica serovar Abortusovis |
| Mydiavac | Inactivated vaccine for the active immunisation of breeding female sheep against C. abortus infection |
| Toxovax | Live, concentrated vaccine containing tachyzoites of the S48 strain of Toxoplasma gondii |
Pregnant women are at major risk for both diseases & avoid all contact with ewes at lambing time
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As cited in the recent NOAH vaccination Guide as Category One, abortion vaccination is highly important for flock management and regarded as a default unless a vet/farmer led justification to not vaccinate with this strategy position regularly reviewed9.
When administering vaccines even at a low dose volume, equipment needs to be simple and reliable ensuring confidence and efficacy delivering an unfailing accurate dose.
Ensure vaccinators deliver the required volume required and follow all instructions carefully
Injectors must be in good working order, are clean with no accumulated debris in the draw off tubes and chamber
Ensure free barrel movement so the correct dosage is drawn up each time, re-lubricate with vegetable (NOT mineral) oil after cleaning if necessary
Calibrate all equipment beforehand including Selectable ‘dial-a-dose’ or fixed dose devices
Bottle mount devices remove the need for delivery tubes and are easier to prime
On tube fed injectors ensure delivery tubes allow free flow of product without kinks or blockages
Make sure adequate handling systems allow sufficient restraining for accurate and stress free treatment
The new generation of injectors such as the Simcro™️ VS with a vertical chamber is ergonomically designed and balanced and can be used comfortably over extended periods of time. This fixed dosage device is extremely accurate. Air is more easily purged as well as any debris which can be spotted and removed easily with clear easy view inlet and outlet chambers. A lockable needle guard minimises accidental needle stick injury. The devices can be broken down and reassembled in seconds for quick cleaning including boiling so are compliant with the most stringent on-farm hygiene regimes. Chambers and valves on the VS range are replaceable and are self-contained with no small components. EID readers from the Tru-Test range and Prattley mobile handling systems assist with identification and more accurate record keeping.