When you think about animal cruelty, you might think of chained-up dogs left to suffer in the cold, stray cats struggling to survive on the streets, or depressed polar bears at the zoo. As terrible as many cats, dogs, and zoo animals have it, the animals that are both the most numerous and that have it worst — by far — are farmed animals.

But the biggest problem they face isn’t necessarily the cruel, overcrowded, unsanitary factory farm, where the vast majority of animals raised for meat, milk, and eggs are confined. Nor is it the inhumanity of the slaughterhouse. Rather, the most severe animal welfare problem in today’s meat industry is largely invisible to the naked eye. I’m talking about their genes.

The most stark example is the chicken, which accounts for around 95 percent of animals raised for food in the US, at 9.4 billion birds. Globally, over 75 billion chickens are slaughtered every year.

Over the last 80 years, the poultry industry has significantly altered chickens’ genetics, breeding them to grow as big as possible in as little time as possible, all in an effort to quickly and efficiently pump out more and more chicken. In 1960, it took nine weeks, or 63 days, in the US for a chicken to reach slaughter weight at a tiny 3.35 pounds.

By 2024, according to the US trade group National Chicken Council, chickens reached slaughter weight in under seven weeks, or 47 days. And they’re nearly twice as heavy as chickens were 65 years ago,........

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