Biologists have a term for stretchy, accommodating digestive equipment: compliant. You’re planning on taking down an ibex? Yes. No problem. I can handle it. The compliant stomach is a physiological larder, a storage unit for the food that will sustain an animal over the days or weeks when prey are scarce or it’s off its game. It is the stomach of feast-or-famine. “The predator has a very compliant stomach,” says David Metz, a gastroenterologist with the Hospital of the University of Pennsylvania who has studied people who compete in eating contests. “Think of the lion after the big meal, with its huge, distended belly. They can lie in the sun for the next few days, letting it all slowly get digested.” When you occupy the top spot on the food chain, you are free to lounge around with little concern over someone larger and stronger jumping you and eating you. The lion falls prey only to humans, in the form of hunters—and the occasional Mesopotamian vivisectionist.
In a 2006 issue of the Lebanese Medical Journal, Farid Haddad details the efforts of Ahmad ibn Aby al’Ash‘ath, a court physician in Iraq circa A.D. 950, to document the compliancy of a lion’s stomach. In his opening paragraph, Dr. Haddad notes that ’ash ‘ath means “disheveled.” It seems an unlikely name for a royal physician, but a brief spin through the man’s writings sheds some light: “When food enters the stomach . . . , its layers get stretched; I observed this in a live lion which I dissected in the presence of Prince Ghadanfar. . . . I proceeded to pour water in the lion’s mouth and continued to pour jug after jug in its throat; and we counted until the stomach filled up with about [5 gallons]. . . . I then cut open the stomach and let the water out; the stomach shrank and I could see the pylorus. God is my witness.”
The agriculturally informed reader may be unimpressed by the five-gallon capacity of the lion’s tank. A cow’s rumen—the largest of its four stomach compartments—is the size of a thirty-gallon trash can. Why should this be, when all a ruminant needs to do to get dinner is lower its head and graze? When food carpets the land from hoof to horizon, famine isn’t a concern. So why the massive intake? The answer lies in the relatively low nutritional value of the ruminant diet. It is not merely the size of the cow’s rumen that resembles a garbage can, it is the contents. The first place I visited for this book was the University of California at Davis, where animal science professor Ed DePeters and his colleagues test organic waste by-products to see whether they might make good cattle feed. With the help of a fistulated cow, DePeters has tested the digestibility of almond hulls, pomegranate scrap, lemon pulp, tomato seeds, and cotton seed hulls. He is a modern-day William Beaumont, lowering mesh bags of experimental foods into the rumen, and then pulling them out by a string at intervals to see what remains. The day I visited, they had been testing prune pits from nearby Yuba City, “the prune capital of the world.”*
Cows, by virtue of the plentiful and varied bacteria in their rumen, are able to derive energy from things that would pass through a human undigested. The prune pit has a hard, nutritionally blank hull, but the embryo inside provides protein and fat. Rumen bacteria can break down the hull and free these nutrients, though it takes them a few days. DePeters showed me one of the mesh bags. “Sometimes I put a midterm exam in there,” he said. Cows can’t digest wood pulp. “I tell my students, ‘The cow didn’t digest that material any better than you did.’”
“We’ve done cloth from a plant in Petaluma that was making cotton towels. All the small linters that didn’t get into the towels? You can feed ’em. They can break it down. They get energy from it. It’s just slower.” As with hay and grass, it takes a sizable serving of tea towel for a cow to get its RDA—hence the enormous volume of the rumen. DePeters speculates that there’s another reason for the huge capacity of the rumen. Ruminants graze on the open plain, easily visible and vulnerable to predators. “So they’ll go out and graze and take in a lot, then go and hide somewhere to ruminate and digest.” The rumen is a built-in to-go box.
DePeters took me to visit one of the fistulated cows. Escorted by an entourage of large flies, we made our way through a grid of muddy corrals. I was in kitten heels and a skirt, a fact from which DePeters, in filth-encrusted rubber boots and worn T-shirt, derived lasting merriment. DePeters is tanned and tall, with a wiry build. His hair is the same reflective silver of the screeching aluminum gates. It works well with his eye color, the deep dusty blue of scrub-jay plumage.