Enzootic abortion (chlamydiosis) is generally caused by Chlamydia psittaci germs. It occurs countrywide and the germs may be found in the intestines of healthy sheep.
They can even cause miscarriages in pregnant women who handle sick sheep or lambs.
The disease usually spreads among sheep during lambing. Sheep pick up the germs by mouth when they graze in an area contaminated by infected afterbirth or infected uterine fluid of lambing ewes. Lambs can be infected at birth too.
Chamydial infection can remain dormant in the ewe lamb until it aborts during the first pregnancy. Outbreaks usually occur within a year or two of bringing infected sheep onto the farm.
The ewe shows no signs of illness, but a flock infected for the first time may have an abortion rate as high as 70%.
Abortions can occur as early as three months, but the foetus is then usually re-absorbed. Ewes may abort in the last month of pregnancy, or give birth to small, weak lambs that die shortly after birth.
Spots of blood above the udder and on the hocks may be the only sign of abortion. Needless to say, you will have a poor lambing rate.
C. psittaci can be treated with prolonged, high doses of certain antibiotics, but this is often impractical or too expensive. Ask your animal health technician or state vet for advice.
Because of lamb deaths and the poor growth of lambs that survive, it is essential to vaccinate. Onderstepoort Biological Products (OBP) produces an oil-based, inactivated vaccine to prevent abortions caused by chlamydial infection.
Pregnant ewes can safely be inoculated, if necessary.
Vaccinate before the breeding season, because the vaccine will not provide protection against abortion once the foetus has been infected. The ideal time is four to six weeks before the breeding season.
Source: Mohale, D: ‘Abortions and causes of death in newborn sheep and goats’ (ARC).