BSE is believed to be linked to CJD in humans
The research by one of the government's top advisers on the disease has found it is virtually impossible that BSE can be passed from an infected cow to her calf.
Professor John Wilesmith fears that as there has been a ban on feeding cattle meat and bone meal in Britain since 1996 any contamination must be coming from another source - possibly infected cargo.
In Professor Wilesmith's experiments, embryos from cows that had the disease were fertilised with semen from infected bulls and put in the womb of surrogate cows. None of the calves or the surrogate mothers contracted BSE.
Experimental results
The BBC reporter Sarah Mukherjee said: "This research is seen as good news by the Department for Environment, Food and Rural Affairs (Defra).
"But it begs the question why cows are still getting the disease - about 500 last year in Britain and hundreds across Europe."
Professor Wilesmith, from the Veterinary Laboratories Agency, told BBC Radio 4's Farming Today programme: "If maternal transmission is occurring, then we have no idea how because everything we have looked at in terms of excretions and secretions from cows have all proved negative.
"My working hypothesis is that we are still dealing with cross contamination but not from a British source but from ships importing [feed] into Britain."
Banned feed
Professor Wilesmith's theory of bone meal contamination is supported by a report presented to the European Parliament earlier this month.
That study said farmers in member states were still feeding their cattle meat and bone meal, which was banned by the EU in 1994.
BSE in cattle is believed to be linked to variant Creutzfeldt-Jacob Disease (CJD) in humans, which is invariably fatal.
Many scientists believe the disease can be passed to humans through infected meat.
According to the UK Creutzfeldt-Jakob Disease Surveillance Unit in Edinburgh, there have been 104 vCJD deaths in Britain since 1995 and nine people have the disease at present.