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Prevention key to avoiding sheep “abortion storm”

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Abortions happen in all livestock species, but with sheep, a lambing season can under some circumstances turn into a full-blown “abortion storm.”

The reason, said Dr. Chris Clark, an assistant professor at the University of Saskatchewan, is that 80 per cent of sheep abortions are caused by highly infectious agents, and character traits that tend to make the problem worse.

“In cattle, it’d be unlikely to see a five per cent abortion rate. In sheep, get the wrong bug at the wrong time and you can up to 60 per cent abortions,” said Clark, in a presentation on sheep biosecurity at the recent Manitoba Sheep Association annual general meeting.

“In my whole career, that has only ever happened once. But it can be very bad.”

Ewes just before lambing will crowd around and lick a dead fetus and amniotic fluid due to maternal instincts. If a bug is present in that material, they ingest it and pass it on to the entire flock.

The most common cause of sheep abortions in Western Canada is chlamydiophila abortus, also known as enzootic abortion in ewes or EAE.

“Chlamydiophila is really in a category all by itself. This is a pure abortion disease. It is common, easy to get onto your farm, very hard to control, and can cause problems for years,” said Clark.

Typically occurring in the last two weeks of pregnancy, it has very clear characteristics. Ewes look “100 per cent” healthy, but go into labour early and abort the fetus. Lambs look normal, if somewhat small, and some may survive for short periods in a very weakened state due to inadequate lung development.

The placenta may provide clues. Normally, it looks like clear poly wrap covered with “buttons.” With chlamydiophila, the area between the buttons may be cloudy or thickened, leathery and yellow in about 30 per cent of cases.

Both fetus and placenta must be sent to the lab for effective diagnosis, he added.


Typically, the disease plays out over two years. No signs are evident until lambing time, when one of the new replacement ewes aborts. That’s because the ewe can carry the bug in a dormant state through breeding and pregnancy up until two weeks before lambing.

The pathogen is then spread to the rest of the flock via contact with the infected fetus or placenta, and through vaginal discharge for up to two months afterwards. The other sheep pick up the bug, but go on to lamb normally that year.

The next year, 10-15 per cent of the flock may abort. The good news is that apart from that one abortion, infected ewes develop lifelong immunity to the disease.

“If a ewe aborts, get the ewe, the lamb and placenta out of the pen, and if you know where she lambed, dig that bedding up,” said Clark.

If an operation is at risk for EAE, a vaccine should be given to new ewes before breeding. For older ewes, a booster is enough. It doesn’t work on already infected ewes, because they will still abort.

Buying replacements in the form of young, virgin ewe lambs is not a fail-safe, because they may have picked up the disease while young and abort on their first pregnancy.

Don’t panic

For producers in the midst of what seems like a disaster, he advises them not to panic. Even if 30 per cent of the lamb crop has been lost to abortions two weeks ahead of the anticipated lambing date, as the rest of the ewes come to full term, live lambs will start arriving.

“That two weeks before lambing when ewes are aborting is soul-destroying, but things will improve,” he said.

For flocks of less than 50 head, an abortion storm may be “dampened” by injecting long-acting oxytetracycline every five days. The drug is not registered for sheep, so a veterinary prescription is necessary. Larger flocks are better treated with medicated feed.

Rams don’t get infected, but could spread it on their penis from an infected ewe to another ewe.

Chlamydiophila is transmissible to humans, so pregnant women and small children should avoid contact with sheep at risk. Don’t bring weakened lambs into the kitchen for nursing, he added.

Biosecurity is critical to profitable shepherding, said Clark. Lambing out replacements their first year in a separate pen is a good idea, if economically possible.

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