Advocates of small-scale, nonindustrial alternatives say their choice is at least more natural. Again, this is a dubious claim. Many farmers who raise chickens on pasture use industrial breeds that have been bred to do one thing well: fatten quickly in confinement. As a result, they can suffer painful leg injuries after several weeks of living a “natural” life pecking around a large pasture. Free-range pigs are routinely affixed with nose rings to prevent them from rooting, which is one of their most basic instincts. In essence, what we see as natural doesn’t necessarily conform to what is natural from the animals’ perspectives.

The economics of alternative animal systems are similarly problematic. Subsidies notwithstanding, the unfortunate reality of commodifying animals is that confinement pays. If the production of meat and dairy was somehow decentralized into small free-range operations, common economic sense suggests that it wouldn’t last. These businesses — no matter how virtuous in intention — would gradually seek a larger market share, cutting corners, increasing stocking density and aiming to fatten animals faster than competitors could. Barring the strictest regulations, it wouldn’t take long for production systems to scale back up to where they started.

All this said, committed advocates of alternative systems make one undeniably important point about the practice called “rotational grazing” or “holistic farming”: the soil absorbs the nutrients from the animals’ manure, allowing grass and other crops to grow without the addition of synthetic fertilizer. As Michael Pollan writes, “It is doubtful you can build a genuinely sustainable agriculture without animals to cycle nutrients.” In other words, raising animals is not only sustainable, but required.

But rotational grazing works better in theory than in practice. Consider Joel Salatin, the guru of nutrient cycling, who employs chickens to enrich his cows’ grazing lands with nutrients. His plan appears to be impressively eco-correct, until we learn that he feeds his chickens with tens of thousands of pounds a year of imported corn and soy feed. This common practice is an economic necessity. Still, if a farmer isn’t growing his own feed, the nutrients going into the soil have been purloined from another, most likely industrial, farm, thereby undermining the benefits of nutrient cycling.

Finally, there is no avoiding the fact that the nutrient cycle is interrupted every time a farmer steps in and slaughters a perfectly healthy manure-generating animal, something that is done before animals live a quarter of their natural lives. When consumers break the nutrient cycle to eat animals, nutrients leave the system of rotationally grazed plots of land (though of course this happens with plant-based systems as well). They land in sewer systems and septic tanks (in the form of human waste) and in landfills and rendering plants (in the form of animal carcasses).