The two-and-a-half-year-old animal, called Brainstorm, is the daughter of a pedigree Jersey cow, Birthday, which was confirmed in a post-mortem examination as having contracted BSE. The case therefore raises the possibility that the disease could have been passed by 'maternal transmission' - either at birth or genetically.
Contaminated feed is thought to be the cause of infection in the majority of BSE cases, but government scientists have not been able to rule out maternal transmission as one route of infection. This could alter the Government's predictions over the numbers of infected animals, and the timing of any fall-off in the number of confirmed cases.
In two animals, officials have been unable to identify a link with feed. Both were born after the ban in July 1988 on using ruminant protein in feed for other ruminants.
This latest case will be particularly embarrassing for the ministry because its officials have quarrelled once before with the farmer who owns Brainstorm, Mark Purdey, over his controversial theories on BSE. He believes pesticides against warble fly infestation can weaken the immune response of cattle, making them susceptible to BSE.
Mr Purdey, of Elworthy, Somerset, was unhappy about the ministry's reaction to his attempts to treat another of his cows, Damson, which contracted BSE, with a radical therapy he devised involving oxime - a chemical used to counter the effects of nerve gas.
Brainstorm gave birth to her own calf two weeks ago. The stress of calving, Mr Purdey said, is thought to prompt symptoms of BSE to appear in infected animals. Mr Purdey said yesterday: 'She looks as if she's stoned. She has a spaced out expression . . . that classic glazed BSE look. She often stands with her nose pressed up against the wall. She is reluctant to come into the milking parlour, and will kick suddenly and violently when the milking clusters are on. She sniffs the ground, has tremors under her skin and licks her lips and back more than usual. She has a weird pulse in the carotid artery, which her mother also had.'
Damson and Birthday were in a group of eight cattle Mr Purdey bought from a farm that uses chemical treatments. He farms by strict organic methods and says that Brainstorm, born after the 1988 feed ban, has only eaten feed that he believes contained no animal protein.
A spokeswoman said the agriculture ministry's usual practice was to slaughter suspected BSE cases immediately if they were born before the feed ban. Animals born after the ban are monitored for three weeks before further action. 'MAFF's concern is with trying to confirm whether or not this is BSE through observing clinical symptoms.'