First, let’s look at the bulk of the beef produced in America today. Generally speaking, American beef cattle spend the majority of their life on grazing lands, and are then rapidly fattened (or “finished”) for a few months in feedlots before they are slaughtered. At any given time, there are approximately 70–80 million beef cattle alive in the United States, with about 60–65 million on grazing lands, and 10–15 million in feedlots. Another ~20 million cattle live in dairy operations. Each year, we slaughter a total of 30–35 million cattle in the United States for meat consumption, mostly from feedlots and by culling dairy herds.

In feedlots, cattle are kept in cramped spaces, fed grains (mainly corn, sorghum, and wheat) and forage (mainly alfalfa and corn silage), and pumped full of a myriad of antibiotics and growth hormones. This helps bring cattle to their slaughter weight very quickly, and with the marbled texture of beef that American consumers have grown accustomed to.

Naturally, keeping millions of cattle in confined feedlot operations creates some problems.

One is the use of antibiotics. Feedlot cattle are not given antibiotics because they are sick, but because antibiotics make the animals fatten faster. Amazingly, livestock use about 70% of the antibiotics consumed in the United States every year, and public health experts are concerned that this could give rise of antibiotic-resistance microbes. To help address this concern, the FDA has recently imposed to new rules to cut back on antibiotic use in animal production. But many fear that this is not enough to reduce the risk of antibiotic-resistant disease outbreaks, which could jump into the human population. This alone raises big questions about feedlot operations.

There are also concerns about animal welfare in feedlots. Scientific evidence shows that cattle in feedlots experience higher levels of stress and digestive problems than grass-fed cattle.

And it doesn’t take much imagination to see that feedlots can have tremendous impacts on the environment.

Communities near feedlot operations often have to contend with manure runoff, water pollution, air pollution, and noxious odors. (I grew up down the road from a concentrated dairy operation, and can attest to this on a personal level.) The manure production of feedlots alone is staggering: Animal feedlots in America (including cattle, hogs, chickens, and other animals) produce an estimated 2 billion tons of manure every year, with no sewage treatment. That’s over 130 times the production of all human feces (estimated at roughly 15 million tons of human feces per year) in the country, which is sent to sewage treatment facilities or septic tanks. And all that animal shit has to go somewhere — a lot of it ending up in our waterways and lakes. It’s painful to even think about it.

But the environmental impact of feedlots goes far beyond the facilities. In fact, vast areas of the country are used to supply the feed needed to operate them. For example, corn alone occupies nearly 100 million acres (about the size of California) of US farmland, where most of it is used to make ethanol and animal feed (for cattle, hogs, chickens, and so on), instead of food people can eat directly. And so the land use, water use, chemical use, and environmental impact of growing this feed is largely driven by ethanol and meat production.

Mostly, it’s just a giant waste of food, because the process of converting corn (or other grains) to edible beef is actually quite inefficient. In fact, it takes about 30 calories of edible corn (which, unlike grass, we humans could eat ourselves) to grow one new calorie of edible beef. Where else do we throw away 29 out of 30 calories in the food system? (I should note that the beef industry likes to quote other feed-to-beef conversion numbers (like 5:1 or 7:1 or 10:1) but they are looking at the weight of the entire animal — including bones, organs, and hides — not the edible food that it produces, either in terms of calories or protein. Moreover, they don’t include the grass or milk that cattle ate over their lifetimes outside the feedlot.) In terms of efficiency, the 30:1 ratio is the most direct way to compare the food we could have eaten (in the form of corn or other grains) versus the food we actually get (in terms of edible, boneless beef).

Cattle are also a major contributor to climate change. Most importantly, cattle burp (not fart) lots of methane, an important greenhouse gas that traps heat about 34 times effectively than carbon dioxide (averaged over 100 years, because methane traps heat even better than this, but doesn’t live as long in the atmosphere). It is important to note that cattle burp methane whether on grazing land or in feedlots, so neither one is ideal for climate change.