February 26, 2002 The Daily Telegraph (London) by Robert UhligIT IS virtually impossible for BSE to be passed from an infected cow to her calf, according to a 12-year study involving hundreds of cattle.
The research, which is due to be published in The Veterinary Record, eliminates the 9.6 per cent statistical risk of transmission that led to the slaughter - in retrospect unnecessary - of 11,443 offspring of BSE-infected cattle.
Professor John Wilesmith, head of epidemiology at the Veterinary Laboratories Agency, which conducted the research, said he was now convinced that the only way cattle could acquire mad cow disease was through eating contaminated food. It should mean that cattle traders have a convincing case to campaign for resumption in the export of embryos, a trade that was banned in March 1996 and which is worth several hundreds of thousand pounds a year.
The study, commissioned by the Ministry of Agriculture and begun in October 1989, involved producing embryos from 13 bulls, eight of which had BSE, and 167 cows, all of which were infected.
A total of 587 embryos were later implanted in 347 heifers imported from New Zealand to ensure they were not infected with BSE.
Of the 266 offspring born, 144 had dual positive parentage, meaning they came from both a BSE-positive bull and a BSE-positive cow.
All the offspring and their surrogate mothers were monitored for seven years and then slaughtered.
The brains of all the animals were examined and neither the offspring nor their surrogate mothers showed any signs of BSE infection.
In another experiment, non-viable embryos were injected into transgenic mice, which were monitored for 700 days after inoculation and then killed. None of the mice brains showed any signs of spongiform lesions.
The researchers also injected samples of uterine fluids from 40 of the BSE-infected donor cows into the brains of mice.
All but one of these mice showed no signs of spongiform lesions. The single positive mouse was discounted as an anomalous result because it died only 47 days after inoculation, which would have been too short for infection.
Prof Wilesmith said: "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."
Some 13 cows with BSE have been born since August 1996, when all use of animal feedstuffs containing meat and bonemeal was banned. Prof Wilesmith said he was convinced that the only way these cows could acquire the disease was through contaminated food.
He said: "I think the concern at the moment that we have is cross-contamination of feedstuffs which have been imported into Britain.
"There is still a possibility that one could get cross-contamination in the holds of ships and so on, because meat and bonemeal has been traded around the world and we know that a certain number of countries actually do have it [BSE]."
Tim Miles, veterinary manager at the Meat and Livestock Commission, said: "This is more reassurance for the consumer about the safety of beef.
"It means the offspring cull was in retrospect an unnecessary belt and braces operation, but at the time the science suggested we should slaughter offspring and it was a safe precaution to follow that advice.
"As this research shows there isn't any maternal transmission, we can press the case to get our embryos exported again."