Gridlocked traffic stretched from junction 10 to junction four of the M6 in the West Midlands after the blood spilt from a tanker during the morning rush-hour.
The tanker was travelling from a slaughterhouse in south-west England when a seal failed, pumping blood across the north-bound carriageway between Wednesbury and Walsall. The blood was from a herd aged over 36 months that was destroyed under the government Bovine Spongiform Encephalopathy regulations.
The Ministry of Agriculture said there was only a very minor risk that the blood was infected with BSE, which had never before been found in blood.
A West Midlands Police spokesman said: "A large quantity of the blood has spilt on to the carriageway. The tanker has pulled on to the hard shoulder and a clean up operation is currently under way."
Four firefighters, two police officers, the tanker driver and his wife were taken to Walsall Manor Hospital to have the blood washed off, the spokesman added.
A spokesman for the Ministry of Agriculture said: "The chances of this blood being infected with BSE are highly remote.
"The independent scientists who advise the Government on measures to control BSE and protect the public have said that blood has never been found to contain BSE infectivity.
"All animals suspected of having BSE are removed from the herd and slaughtered and incinerated," he said.
All cattle slaughtered for food in the UK are killed before they reach 30 months. But he said the fact that the blood came from cows aged over 36 months suggested it was from milk cows that had come to the end of their working lives and were destroyed so they could not enter the food chain.Reuse content