European experts on mad-cow disease say that Canada should ban the use of meat and bone meal in all animal feed if it wants to minimize the risk of transmitting the disease among cattle.
Like the United States, Canada has forbidden the use of ruminant meat and bone meal in feed destined for cattle and other ruminants since 1997 but has continued to permit the same material in other feed, as long as it is destined for poultry and hogs.
But the Europeans have learned from the sad experience of Britain -- where bovine spongiform encephalopathy was first detected in the late 1980s, costing the farming industry billions of dollars -- that a partial ban is insufficient.
The use of any ground-up animals in feed destined for other animals has been banned in Britain since 1996 and across the European Union since 2000.
The problem is that feed containing potentially infectious bone and meat material can easily end up being fed to cattle by accidental mixing at feed mills or on purpose by farmers anxious to cut corners.
Scientists believe that BSE is transmitted primarily when cattle consume feed containing protein from infected cattle.
"There is no other known route of transmission," said Marcus Doherr, senior researcher in veterinary epidemiology at the University of Bern in Switzerland. He says the partial ban on meat and bone meal in Canada and the United States leaves a loophole that allows infected material to enter the food chain.
"Ruminant feed can still end up in other cattle feed even if it is not on purpose," he said. "It's accidental contamination that cannot be prevented if it's produced in the same feed mill.
"If your first batch is non-cattle and you have meat and bone meal in there, in the beginning of the next batch you will have that cross-contamination," he continued. "You end up with ruminant protein in the ruminant batches even if it was not intended."
Farmers can also be to blame. "If you have a farm that has cattle, pigs and poultry and they are storing and feeding all these feeds, as long as you have ruminant protein in your other livestock feed, there is still the potential of exposure of calves to pig feed or whatever."
Mac Johnston, professor of veterinary public health at the Royal Veterinary College in Britain, said, "There are just so many areas where crossover can take place."
He cites the hypothetical example of a farmer who goes to his local feed mill looking for calf feed but discovers that there is none left in stock.
Instead, the feed mill operator suggests using turkey feed, which is a cheaper substitute but acceptable to calves. The farmer agrees and inadvertently may feed BSE-infected meat and bone meal to his calves.
Then there are farmers who simply don't bother reading labels and give hog feed to cattle, Dr. Johnston says.
Another problem is that meal is highly electrostatic and tends to stick to metal parts of machinery. "It's a helluva job cleaning a feed mill," Dr. Johnston said.
Jessica Eriksson, senior veterinary officer at the Finnish Department of Agriculture, says allowing meat and bone meal to be included in any animal feed "is a huge danger." Finland reported its first and only case of BSE in a dairy cow in 2001.
"The danger for contamination is in transportation," Ms. Eriksson said. Feed containing meat and bone meal is delivered in bulk, she said, and some of it can get left behind in corners of the truck and then get mixed in with the next batch of feed being delivered in the same truck. If that feed is destined for cattle, contamination can result.
Banning meat and bone meal in all feed comes at a substantial cost because of the need to incinerate any leftover part of the slaughtered animal. Europeans use only 40 to 45 per cent of a typical carcass, compared with 60 to 65 per cent a decade ago, Switzerland's Mr. Doherr said. The rest is burned.