Scientists from the Government's Institute for Animal Health in Berkshire have reported that between 85 and 98 per cent of the cattle are positive for antibodies to bovine immunodeficiency virus (BIV), a relative of the human Aids virus.
However, the researchers need to carry out two further tests over the coming months to make sure the animals are really positive for BIV, which would be the first time the virus has been confirmed in Britain.
Tim Blything, the dairy farmer, said the results show that the virus is infectious and he wants the Ministry of Agriculture, Fisheries and Food to quarantine the herd and pay compensation.
Ministry officials, however, said there was no evidence that BIV could be passed easily between livestock, and experience in the US suggests it is not dangerous to either cattle or humans, and that drinking milk from BIV-infected cattle is harmless.
The Milk Marketing Board, has nevertheless written to Mr Blything saying it will not collect milk from his farm because of its concern 'that the general public's image of milk should not be tarnished' and it felt 'a duty . . . to prevent a public scare'.
Mr Blything's wife, Linda, said the results of the blood tests showed that animals born on the farm and kept separate from cows imported from the Netherlands and Germany remained free of BIV. Others that mixed with the imported cows were positive, which showed that the virus appeared to be highly infectious, contrary to the Ministry's assertions, she said.
Joe Brownlie, the BIV specialist at the Institute for Animal Health, said he could not comment in detail on the results.
'There seems to be a growing awareness of an association between a high level of BIV antibodies and general ill- health in cattle in certain herds. The overall feeling is that there is a high level of antibodies to BIV in this herd.'
Keith Meldrum, the Government's chief veterinary officer, said he had approved further research into the herd to find out the precise relationship between BIV and the illnesses seen in the cattle.
Every animal in the 100- strong herd has developed some form of sickness. Many of the symptoms, such as muscle- wasting, ulcers, skin lesions and respiratory difficulties, are similar to human Aids.
Mr and Mrs Blything first noticed the problems last year after the imported cattle arrived on the farm.
They called in government vets last autumn, but it was only in February - after an article in the Independent on Sunday - that their predicament came to light.
Mr Blything's family has been farming for five generations and he can find no apparent reason why his livestock should suffer such severe debilitating illnesses that the animals cannot seem to recover.
Officials at the Ministry of Agriculture said that animals with BIV make a full clinical recovery, but Mr Blything has witnessed the death of many of his prize animals.
He now faces financial ruin because of the Milk Marketing Board's decision to stop paying for milk from next month.