ONE of the biggest causes of abortion in ewes may be passed down from generation to generation.

Cats and their faeces have always been blamed as the main source of toxoplasma, but a meeting in Wensleydale last week heard there was now evidence that some sheep families may be susceptible.

Dr Judith Smith, from Leeds University, accepted it was a highly radical idea, but one she intends to fully investigate. If it proved correct, she suggested some farmers may even consider culling out susceptible ewes.

She stressed the theory was at a very tentative stage, based on trials involving just one flock.

"But it is something we really need to look at seriously," she told the meeting, organised by Carr's Billington, at the Fountain Hotel in Hawes. "It could turn around the way we think of controlling this disease."

Dr Smith carried out a study in Worcestershire where she was looking at the level of toxoplasma among aborted and live Suffolk X lambs.

The results showed far higher levels than expected - 94pc of aborted lambs were toxoplasma positive and 42pc of umbilical cords from live lambs were infected. "The transmission of the parasite was very high, and when we looked at others they were all similar,"

In Charollais sheep the figures were 96pc and 43pc respectively and 100pc and 36pc.

Dr Smith chose the pedigree flock because of its detailed records going back ten years. "We could trace each ewe and if we did have this vertical transmission from the ewe to the daughter to the grand-daughter we would expect some families to have a higher rate and others a lower rate," said Dr Smith.

"Looking at individual families was quite shocking; we had everything from 36pc, which was extraordinarily high, to 7pc and nil. Within this flock there was a link between abortion and toxoplasma."

Dr Smith said the cat was still an important route for the infection. "But I think we have to open our eyes and do a bit more work on whether this second congenital track is a key."

Dr Smith believed much wider research could be done using pedigree flocks and their records. If further research supports the initial findings, farmers may decide not to keep ewes that abort to avoid keeping a susceptible animal and susceptible genes.

She had earlier explained that toxoplasma was the commonest parasite in the world, occurring in all mammals, including 20pc of humans, and birds worldwide. It originated in cats whose faeces passed it on to pasture. They had always been regarded as the major source of infection with vets advising farmers not to keep them on the farm.

It was then picked up by other animals which developed flu-like symptoms before their immune system kicked in. At that point the toxoplasma forms cysts in brain cells and muscles and remained in the host for life.

Earlier, John Naylor from Carrs Billington spoke about staggers in sheep, which was caused by a lack of calcium: at its worst a ewe could not stand and went blind.

It occurred during the last three to four weeks of pregnancy, was caused by stress and often occurred when the ewes were moved, eg to better pasture. The age of the ewe and the number of lambs she was carrying also increased the danger.

"I have seen it a lot more in Swales than any other breed but I have also seen it in Mules and Blackies, " said Mr Naylor, who said farmers could minimise the risk by minimising stress during the last few weeks before lambing.

Good nutrition was essential . If there was an historic problem with staggers, a concentrate should be used, balanced with forage. The higher the phosphorous/calcium level the better, but the magnesium level should be minimised during pregnancy as it inhibited calcium absorption. However, it should be fed post-lambing.