In its quest to grow ever-bigger chickens to meet growing demand for white meat, the food industry has hit an unexpected problem.

The trouble isn't raising large-enough birds. A growing share of broiler chickens—bred for meat, not to lay eggs—now can yield a pair of breast fillets that are heavier than an entire bird was a few decades ago. A rising number of those fillets are laced with hard fibers in a condition the industry calls woody breast. It poses no threat to human health, but it degrades the texture of the meat.

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