Focus lambing: Dealing with an abortion storm

Supplies of the three vaccines available against Chlamydial abortion, or what is commonly known as enzootic abortion, were all affected to various degrees last autumn.

The two most commonly used vaccines, Enzovax, manufactured by MSD Animal Health and Cevac Chlamydia, manufactured by Ceva, were unavailable for the majority of the season.

While supplies of the third vaccine Inmeva, manufactured by Hipra, provided a reprieve for many flocks but were unable to service all of the additional demand.

As a result some flocks on a vaccination programme were not in a position to vaccinate replacements while some other unvaccinated flocks with issues last spring were unable to adopt vaccination.

It is worth noting that many flocks vaccinating for years may not see any knock on consequences of not vaccinating for one year if the disease challenge is at a low level in the environment.

The likelihood of further cases in flocks which experienced issues at the last lambing is much higher.

This is due to the fact that disease can spread rapidly in an unvaccinated flock from aborted material, with chlamydia infection present in discharge for two weeks and bedding for up to six weeks.

Ewes that suffer from the disease in one year are unlikely to abort in later years (depending on the level of prevalence in the flock) but act as a disease reservoir.

The disease can remain silent in ewes until the following lambing with affected ewes possibly aborting at day 90 of gestation. The prevalence as outlined in Table 1 can be anywhere from 5% to 30%.

The first task once an animal aborts is to isolate the ewe from the lambing flock and remove the aborted material and contaminated bedding from the pen. Vets also major on the importance of thoroughly cleaning and disinfecting the area before bringing in more sheep.

Also, do not foster potential replacement ewe lambs onto ewes that have aborted as this will develop a reservoir of disease for future years.

Record the tags numbers or mark aborting ewes to allow easy identification for future treatment or blood sampling, if required. Refrain from mixing ewes that have aborted with pregnant sheep or next year’s replacements until you have a diagnosis of the cause of abortion and have taken advice on the best course of action.

Always remember that aborted material is an infection risk – therefore ensure you use gloves and protective clothing and transport samples in leak-proof containers. It is also vital to be mindful of the fact that many abortion-causing diseases in sheep are zoonotic and are harmful to pregnant women, the young and elderly and those on drugs that cause immunosuppression (e.g. cancer chemotherapy).

There are no treatment options per se for enzootic abortion but strategic use of antibiotics can lessen its impact. Administering oxytetracycline to remaining pregnant ewes on the back of veterinary advice can increase the number of live lambs born. The success of this will be influenced on timing of administration.

Ewes should be treated at day 100, or after a diagnosis has been made, and again at day 120, or 20 days later. This response is most useful in a spread out lambing pattern with the majority of abortions likely to have already taken place in a tight lambing flock.

Losses due to abortion of over 2% suggest an infection is present but failing to take action until losses reach this level is strongly advised against.

A prompt response can limit the spread of infection for that lambing and for subsequent years.

As there are several causes of abortion an accurate diagnosis is vital.

The best samples to achieve a diagnosis of abortion is a foetus, along with the placenta, and a blood sample.

The Regional Veterinary Laboratories advise that multiple abortions may occur around the same time and submitting a number of samples achieves a batch rate and greatly increases the chances of identifying the cause.

The main infectious agents causing abortion, the timing of when they are likely to hit and the likely occurrence rate are detailed in Table 1.

Some causes of abortion are often sporadic and hit for a year and can then disappear.

A good example is Listeria which is caused by feeding poorly preserved silage that has typically been saved in wet conditions that caused soil contamination.

The damage caused by toxoplasmosis in ewes is dependent on the timing of infection and immune status of the ewes, with previously infected ewes developing immunity for life.

Where a naïve pregnant animal is infected in the first 60 days of gestation the result is usually absorption of the foetus and the ewe identified as barren.

A higher than normal barren rate can be a tell-tale sign of issues.

Where infection occurs between day 60 and day 120 of gestation the disease, toxoplasmosis, manifests in abortion in late pregnancy and mummified foetuses or the delivery of stillborn lambs or weak lambs which succumb to high levels of mortality.

There is a lag phase from infection in the ewe to expression of clinical symptoms of approximately six weeks but this can be reduced to four weeks where there is a high challenge in the environment.

Therefore the damage is already likely to be done when the disease manifests itself.

Therefore if concerned farmers were to fully avoid risks from feeding hay there is only a short window in late pregnancy where such forage could be fed with full confidence that it will not be related to issues.

While the incidence of enzootic abortion is on the rise, the agent responsible for the highest level of abortion seen by the veterinary laboratories has traditionally been caused by toxoplasmosis.

Clinical symptoms are similar to enzootic abortion, with cases of abortion in late pregnancy, the birth of mummified foetuses and the birth of weak lambs that struggle to survive.

There is nothing that can be done in the case of an outbreak, while the time period to put preventative measures in place has passed for a high percentage of flocks.

This is due to the manner in which the disease spreads.

Cats are the main route of infection, with toxoplasmosis oocysts shed for a short period of time during the transition from weaning to young cats first starting to hunt.

The infection in cats is caused by the ingestion of infected rodents, with oocysts multiplying rapidly and exponentially in the cat.

The cat will become immune after a few weeks and cease shedding of oocysts, but during this period oocysts can be shed on feed, pasture and the wider environment.

Young cats urinating on hay or straw that ewes consume is the greatest threat.

It should also be pointed out that there can still be sporadic issues, even where hay is not fed, as the source of infection for toxoplasmosis can extend further, with oocysts picked up from other sources, such as feed being contaminated before feeding and pasture, but these sources are less of a risk, with cats defecating on hay and straw that sheep are eating by far being the highest risk.

Control options include keeping the population of rodents at bay and breeding management in farm cats, while the most successful control option is administering the Toxovax vaccine to replacements entering the flock.

The timeframe for this has passed as the vaccine must be administered three weeks pre-breeding.

Not all cases of abortion are caused by toxoplasmosis as detailed in Table 1. Listeriosis, which is commonly associated with feeding poorly preserved silage that has been saved in wet conditions that caused soil contamination.

The causative bacteria, listeria monocytogenes, has the highest risk of being present where silage has preserved poorly and soil contamination is caused by the harvester picking up soil or swards becoming contaminated by traffic in wet weather.

It can also occur despite feeding good-quality silage with issues arising from bad pit face / bale management or allowing feed to go stale and topping up feed on silage that has spoiled or gone mouldy.

The classical symptoms are paralyses on one side of an animal’s face with saliva dripping from an animal’s mouth in advanced cases (inability to chew or swallow).

An animal’s head will generally be tilted to one side with its ear dropped downwards. Animals are also likely to be unsteady on their feet and appear to propel themselves to one side resulting in a circling motion due to paralyses.

Early detection will influence the success of treatment and includes administering a course of antibiotics prescribed by a veterinary surgeon. Ewes in late pregnancy should be given glucose or glycerol supplements to maintain energy intake and help prevent dehydration or twin lamb disease. Ewes will typically abort lambs as a consequence of treatment or the disease while ewes contracting twin lamb disease as a result is also another trigger for ewes to abort lambs during treatment.

Campylobacter and salmonella will also trigger abortion but both are much less frequent in ewe flocks.

The range of causes shows the importance of making an accurate diagnosis.

Sporadic cases of abortion can also be linked to management practices. Ewes with insufficient feeding space can abort due to injuries picked up when competing for space at the feeding barrier while injuries due to rough handling can also trigger problems. As mentioned already twin lamb disease is another management-related issue.

In short