"We've never been able to do much testing to say, 'Yes, it (the ban) is effective,' or, 'No, it is not,"' said Sergio Tolusso, feed program co-ordinator for the Canadian Food Inspection Agency.

"We weren't exactly sure what we would find once we started looking," Tolusso told Reuters in an interview.

Interim results from the study, obtained by The Vancouver Sun through access to information laws, found 41 out of 70 feed samples contained animal materials that were not identified on their labels.

"In several cases, we did see things in the sample that were not supposed to be there," Tolusso said.

"Not all of the results are problematic," he said, adding the study was too small to draw many conclusions.

The program tested 110 samples in total, but Tolusso said he did not know how many contained animal protein.

Some of the materials found were hairs, feathers, bone and muscle fragments, blood and milk, Tolusso said.

The tests can distinguish between poultry and mammalian materials, but are not detailed enough to tell whether the material was from cattle, hogs, or other mammals, he said.

Cattle feed is allowed to contain protein made from hogs and poultry, while pig and poultry feed can contain any animal protein.

Inspectors followed up with the feed makers that provided the samples to see what steps they were taking to prevent cross-contamination, but Tolusso said he did not know whether any were found to be breaking rules.

"We haven't quite completed the follow-up and the overall analysis of the project," he said.

Tolusso said the findings should not concern consumers, because Canada has a very low level of mad cow disease.

"The feed ban that we have had in place, even if it had some potential design flaws, it has been effective in preventing the disease from spreading," he said.

Canada has found one home-grown case of the disease in May 2003. Another case in the United States last December was also traced to a cow born in Canada.

The CFIA inspects feed plants and their procedures, but acknowledges that cross-contamination can sometimes occur, Tolusso said.

That's why the agency has proposed tougher new feed rules that would ban from all animal feed the brains, spines and other risk materials from older animals thought to harbor the agents that cause mad cow disease, he said.

The materials have already been banned from the human food supply, Tolusso noted.

The new rules have been published in the federal government's official Canada Gazette for public comment until Feb. 24, but there is no timetable for their implementation.

Tolusso said the CFIA is debating whether to continue doing microscopic tests of feed because they are labor intensive and inconclusive.