First published: 2017

Author: Maryn McKenna

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Incredible book about the history of chicken farming and how antibiotics contributed to it. The result: It’s undermining current drugs’ usefulness.

I’m not going to lie—this book made me avoid chicken for a while.

Main Takeaways

  • 80% of the antibiotics sold in the United States and more than half of those sold around the world are used in animals, not in humans.
  • Antibiotics are given to make food animals put on weight more quickly than they would otherwise, or to protect food animals from illnesses that the crowded conditions of livestock production make them vulnerable to.
  • Nearly two-thirds of the antibiotics that are used for those purposes are compounds that are also used against human illness—which means that when resistance against the farm use of those drugs arises, it undermines the drugs’ usefulness in human medicine as well.


  • I discovered that the reason American chicken tastes so different from those I ate everywhere else was that in the United States, we breed for everything but flavor: for abundance, for consistency, for speed.
  • Antibiotics have been so difficult to root out of modern meat because, in a crucial way, they created it. The drugs made it irresistible to load more animals into barns and protected animals and their growers from the consequences of that crowding. The escalating spiral of production drove down prices, making meat a cheap commodity, but it also drove down profits, undermining independent farmers and fostering the growth of global corporations.
  • Today, a meat chicken’s slaughter weight is twice what it was 70 years ago and is achieved in half the time. Across those decades, chicken went from a scarce and expensive Sunday treat to the meat that Americans eat more often than any other and that is growing fastest in consumption around the world.
  • Those younger researchers confirmed this discovery that genes conferring antibiotic resistance could stack up on plasmids and be carried from one bacterium to another as the plasmid moved. That would allow an organism to acquire resistance in advance of ever being exposed to a drug, while also allowing multiple types of resistance to spread.
  • The process would go like this: Imagine that within a colony of bacteria, a few organisms harboured a plasmid containing the genes for resistance to drugs A, B, and C. Then imagine that just one of those drugs—B, let’s speculate—was used against the colony. All the vulnerable bacteria would die, but the bacteria containing the plasmid would be protected. In surviving, they would preserve all of the resistance genes within the plasmid—not just B, but A and C as well—and make them available to be passed on to other bacteria, separately or together, horizontally in the same generation or vertically when the plasmid was inherited by daughter cells.
  • The narrowing of the market was probably a natural consequence of the cost of sustaining breeding programs. Keeping the traits in a modern broiler balanced and consistent requires constant breeding of parent, grandparent, and great-grandparent flocks that may total hundreds of thousands of birds. Isolating and adding a new trait, without losing or unbalancing anything the birds already possessed, could take years. The time and expense not only discouraged other firms from entering the business, it also forced rapid consolidation.
  • By 2013, just three companies owned the genetics of almost all of the billions of broilers produced every year worldwide: Cobb-Vantress; Aviagen, which included Arbor Acres; and, in Europe, Groupe Grimaud.
  • The birds that emerge from modern breeding programs—the Cornish Cross that Vantress developed and similar ones produced by the other two companies under different names—look nothing like the old purebreds. For one thing, they are always white; companies realized early that light-feathered chickens appear cleaner and more appealing after defeathering than ones with dark pinfeathers still in the skin. For another, they are disproportionate: They have been bred to bulk up the most in the breast muscles, which are the white meat that American eaters prefer.
  • The breasts on today’s broilers are twice the size of those in the purebred birds that predated them and can account for one-fifth of a bird’s whole body. Those muscles develop faster than the bones and tendons that support them—six weeks, a modern broiler’s age at slaughter, would be barely preteen in a purebred chicken—and the weight unbalances birds’ bodies. A fast-growth broiler has the teetering instability of an olive propped up on two toothpicks.
  • Researchers have found resistance bacteria in the soil around chicken farms, in groundwater under hog farms, and in dust borne away from an intensive farm by the wind. The trucks that bear chickens from farm to slaughter, stacked up in towers of wire cages, stream a plume of resistant bacteria behind them that can contaminate cars on the same road. Scientists have found resistant bacteria being carried away by flies from chicken farms in Delaware and Maryland and hog farms in Kansas and North Carolina.
  • About one-third of a chicken’s weight at slaughter is inedible, so the almost nine billion chickens killed each year in the United States leave behind billions of pounds of viscera, bones, and feathers that are recycled into a granulated feed additive. (In 2012, researchers found that “feather meal” originating with industrial poultry was carrying undetected antibiotic residues back into chickens’ diets.)
  • In 2015, USDA economists calculated that withdrawing growth promoters from U.S farms would make a productivity difference of as little as one percent.
    • The most likely explanation was that growth promoters had never really conferred a benefit; instead, they had compensated for deficiencies in how farms were run, and those deficiencies no longer existed. In fact, in the 1950s, researchers had noted that when animals were raised in very clean conditions, in an experiment or on a farm, they gained less weight from growth promoters than average farm animals did. Seven decades later, better farm hygiene and monitoring, and industrially precise nutrition, had improved farms so much that growth promoters no longer made a difference.
  • In most big plants, chickens travel from farms in cages stacked in layers. They are pulled from transport crates and flopped upside-down while alive and alert, then put into ankle shackles attached to an always-moving chain. the chain drags them through an electrified bath to zap them into unconsciousness, then past a rotating knife that slits their throats, and finally into the scalding tank to loosen their feathers.
  • Sechler paid millions to install a gas-stunning system. At this farms, chickens are inserted into containers like drawers that slot into racks like a massive office organizer. At the plant, the drawers are loaded into a tunnel filled with carbon dioxide that renders the birds permanently unconscious. On the far side, the chickens are fitted by their feet into the horizontal chain, and once dead and gutted, pulled slowly on a four-mile path through refrigerated chambers, “air chilling” instead of cooling in a bath of chlorinated ice that could spread disease organisms.
  • Meanwhile, the drawers keep going along a conveyor belt, traversing an arrangement like a giant dishwasher that sanitizes them before they are returend to the racks and the company-owned trucks.
  • Antibiotic resistance is like climate change: It is an overwhelming threat, created over decades by millions of individual decisions and reinforced by the actions of industries. It is also like climate change in that the industrialized West and the emerging economics of the global South are at odds. One quadrant of the globe already enjoyed the cheap protein of factory farming and now regrets it; the other would like not to forgo its chance. And it is additionally like climate change because individual action feels inadequate, like buying a fluorescent lightbulb while watching a polar bear drown.