They provide us with beef and milk, the gel coating for pills, soap, ice cream, baseballs, and printing ink. But our dependence on cattle, especially the beef we consume in larger quantities per person than any other country except Argentina and Luxembourg, comes at a cost: industrial feedlots where cattle stand knee-deep in their own feces, pumped full of antibiotics and growth hormones for them; clogged arteries, obesity, and heart attacks for us.

From their home in Seattle, husband-and-wife team Denis Hayes and Gail Boyer Hayes, authors of Cowed: The Hidden Impact of 93 Million Cows on America's Health, Economy, Politics, Culture, and Environment, explain why Julius Caesar feared aurochs; how "ag gag" laws are being used in America to suppress criticism of the meat industry; why a cow called Yvonne became a folk heroine in Germany; and how a ranch in Hawaii offers a sustainable alternative to industrial beef-farming.

The book was inspired by a journey to the British Isles and Ireland. What did you find there that intrigued you?

What we found was the aftermath of mad cow disease. We stayed at some country inns where there had been cattle farms and tragedy. In one case, the man of the house had committed suicide as everything fell apart around him. Ironically, his wife served us brisket. [Laughs] The positive part was driving around the countryside and seeing small herds of wildly diverse cows. In the United States you can drive for miles and never see a cow. They are in largest part now confined to huge, concentration camp–style feedlots. The cattle are also pretty uniform.

There was so much diversity in the cows in the British Isles that Gale started compiling the cow equivalent of a birder’s list. Every time she saw a cow, she would draw a picture of it. Then we would try and figure out what kind it was.

Obvious question: Where do cows come from?

The progenitor of the cow is this marvelous beast called an aurochs, which you can see in cave paintings. They faintly resemble cows, and buffalo. They were fierce, smart, and fast, and they instilled terror in people who confronted them in the wild. Julius Caesar famously worried about his troops encountering aurochs. They brought aurochs in to fight gladiators in the Colosseum. Somewhere along the line, someone started milking one, and slowly, over time, that once wild creature was bred into 800 different breeds of cow. The aurochs itself is no longer in the world. The last one was killed about 300 years ago in Poland. But it left behind a huge population of what we now call cattle.