The seven-year experiment, being run by the Central Veterinary Laboratory, involves 630 cows, half of them born to mothers showing signs of BSE, or mad cow disease. It is due to end next year but Sheila Gore, of the Medical Research Council's bio-statistics unit, says that public health requirements mean the results should be checked earlier.
She says the growing number of cases of the degenerative brain disorder Creutzfeldt-Jakob Disease (CJD) among young adults (see table) means data about whether any of the "spongiform encephalopathies" - the class of disease to which CJD and BSE belong - can be passed from mother to child should be made available now. One of the victims of CJD died shortly after giving birth.
"The data about maternal transmission aren't that good in most species," said Ms Gore. "But doing this is not being alarmist, it is acknowledging that this is a question which must properly be asked, and we should get the data to answer it. Presently, we have virtually no data."
In the past two years 10 people aged under 42 have died in Britain from a new strain of CJD. Scientists advising the Government have said that their best hypothesis is that the disease was contracted by exposure to BSE-infected materials. But there is so far no evidence of an epidemic of CJD. Figures from the National Surveillance Unit show the number of suspected cases so far this year is no higher than in 1994.
To date, more than 40 of the calves in the experiment have died of BSE. But the Ministry of Agriculture, Fisheries and Food (MAFF) said this could be because they had eaten infected feed while young.
The experiment is being carried out using a "double blind", so that neither those working on it, nor those monitoring it know which calves came from infected mothers. This data is contained in codes which will be broken at the end of the experiment.
The answer could also affect the culling policy being decided now by Douglas Hogg, the Minister of Agriculture, because if BSE can be passed on in the womb but not between cows, then the present policy of killing any cow aged over 30 months will wipe out many healthy cows while allowing infected young cows to survive, and pass the disease on.
The ministry said yesterday that to end the experiment early would "reduce its power" and could lead to a "false negative", suggesting that the disease could not be passed on where in fact it could. MAFF also dismissed suggestions by researchers in the United States that BSE might not have come from sheep but might instead be a disease particular to cattle.
A ministry spokesman said: "We think it's most likely that BSE originated from scrapie- infected feed."
Meanwhile, Japanese researchers say they have found the role of the cell protein which becomes abnormally shaped in BSE and CJD. Experiments in mice which could not produce the normal form of the protein, known as PrP, showed that it helps keep key brain cells - known as Purkinje cells - alive. Without PrP, the mice lost control of limbs.
This suggests that it is not build up of the abnormal form of PrP - which leads to "plaques" in victims' brains - but the lack of the normal form which leads to the brain disorders typical of CJD and BSE.Reuse content