A late-night call recently was from a farmer who was having difficulty with a ewe lambing.

The ewe was passing an unusual discharge and was not progressing with labour; she had been scanned in-lamb with twins. On examination, she had a lamb which was presented upside down. After correcting the lamb’s presentation and delivering it, I went looking for the second lamb.

This lamb turned out to be dead, decomposed and dried out. The interesting thing in this situation was that the first lamb was alive and appeared to be in good condition.

A sample was taken from the dead lamb for laboratory analysis, which showed that the lamb was infected with toxoplasmosis.

Diagnosis of the cause of the abortion is very useful when deciding what to do with the rest of the flock.

The fact that this ewe was infected with toxoplasmosis meant that our choices for treatment of the rest of the flock were limited.

However, we did advise the farmer that the replacement ewes in the flock next year should be vaccinated against toxoplasma .

We have had other cases of aborted or weak lambs where samples from the foetus showed that Chlamydia abortus or enzootic abortion was the cause of abortion.

In this situation, we advised treating the remainder of the flock with long-acting antibiotics, isolation of any aborting ewes and vaccination of all ewes before going to the ram in the following season.

Additionally, ewe lambs which come into contact with ewes which abort with enzootic abortion should not be kept for breeding.

There are several causes of infectious abortion in sheep. However, toxoplasmosis and enzootic abortion account for approximately two thirds of all diagnosed cases.

Accurate diagnosis of the cause of abortion as early as possible in the outbreak can assist greatly in the management of the disease.

John Gilmore is a practising vet and managing director of Farmlab Diagnostics, an animal health testing laboratory. See www.farmlab.ie.