Mad cow disease, or BSE, first rose to global prominence in the 1990s with an explosive outbreak in the UK. The epidemic was transmitted when livestock routinely were fed protein supplements inclusive of contaminated cow spinal columns, brain tissues and intestines, which harbor the highest concentrations of infectious agents. Since then, the World Health Organization has called for the exclusion of the riskiest bovine tissues from food supply and all animal feed. However, in the US, high-tech cannibalism — the use of performance-enhancing dairy feed whose protein comes from slaughterhouse waste, blood and manure to feed farm animals — still prevails. This common practice has forced natural herbivores like cows to be carnivores and cannibals. In this way, BSE-inducing prions — the infectious protein that causes brain cells to die and form sponge-like holes in the brain — may complete the circuit blamed for the spread of the fatal, incurable disease.
To the cattle industry, feed expenditures remain the single largest cost. While dairy producers can use corn or soybeans as protein feed supplements, poultry waste and slaughterhouse by-products are way much cheaper. Not surprisingly, most newborn calves, separated from their mothers immediately after birth, are fed milk replacer, which mainly contains spray-dried cattle blood as a cheap source of protein. Besides, as few as one thousand chickens can make tons of feces enough to feed a growing calf year-round. According to taste panels, the blood-based milk and manure don't seem to affect the taste of subsequent meat; beef from steers fed bird dropping is in fact more juicy and tender. Though dairy farmers argue the manure's feed value and environmental attributes, the practice simply can't stand up to scientific scrutiny.
The latest discovery of mad cow disease in a California dairy farm this April was a stroke of luck. Nearly 34 million cattle are slaughtered every year in the US. Of those, only 40,000 are tested for BSE. That's about one in every thousand animals. If we tested 80,000, would we find two? Let’s hope this new incident will invigorate consumer campaigns to close the loopholes in feed regulations.
Q: What can’t the reader infer from this article?
A. Mad cow disease is most commonly spread in herds through contaminated feed.
B. Humans can contract BSE by eating brian or spinal tissues from infected cattle.
C. As long as the infected cow doesn’t enter the human food chain, all beef and dairy supplies are safe.
D. Many cattle are fattened on rations that include manure and rendered slaughterhouse waste.
閱讀解答：
C
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