Holes in the USDA's BSE testing system

For example, tests were conducted at fewer than 100 of the 700 plants known to slaughter cattle. Cows from the top four beef producing states, which account for nearly 70 per cent of all cattle slaughtered each year in the United States, only accounted for 11 per cent of all the animals screened.

And though dairy cattle are considered the most likely to develop mad cow, some of the top dairy slaughtering plants were sampled only a few times or not at all.

Experts are worried. A US professor believes that there is a possibility that the US could be harbouring more cases of BSE, and is demanding that all cows be tested.

"The American public should be concerned, at this moment, there is contaminated beef sitting in grocery stores and personal freezers across the country,"​ said Northeastern University​ professor of chemistry Ira Krull.

Krull, a strong advocate for mandatory mad cow testing of all slaughtered cows intended for market, suggests the United States follow the lead of countries such as the UK and Japan. Britain, in response to its mad cow disease epidemic in the 1980s and 1990s, instigated mandatory testing of all slaughtered cows intended for market, keeps detailed records of all cows within its borders, and banned the use of all ruminant feed. Currently, the United States and Canada lag on all accounts, said Krull.

"It's disturbing that, even with a confirmed case of mad cow disease, slaughtered cows are not tested for the disease before they are sent to market,"​ said Krull. Approximately 0.03 per cent of US slaughtered cattle are randomly tested for mad cow disease by the United States Department of Agriculture each year. For the USDA​ to mandate regular testing of every cow for mad cow disease would cost an additional $20 to $25 per cow, which translates into an increase of six cents per pound of beef.

Krull says the issue of testing for mad cow disease is highly political. The more cattle tested, the more likely it is that some will be found with the disease. "They don't want to find it,"​ said Krull. "The USDA really should be funding this like crazy, but it's not."​

The practice of providing ruminant feed to farm animals has been acknowledged to be extremely dangerous, said Krull. The high concentration of nerve and brain tissue in ruminant feed is thought to greatly increase the risk of transmission of mad cow disease. In the 1990s, the US, along with most other beef-producing nations, introduced a ban on ruminant feed, but Krull points out the problem of regulation remains.

"Currently, there is no way to prevent small farmers from making and using ruminant feed,"​ said Krull.

Krull, with assistant chemistry professor Norman Chiu, is working to develop an antimortem clinical test, or assay, to detect chronic wasting disease, a variant of mad cow that affects deer and elk. Current tests for such diseases - known collectively as transmissible spongiform encephalopathies, for the sponge-like formations they cause in the brain - are effective only on slaughtered animals because brain tissue is needed to confirm a diagnosis.