The thing that hooked Debbie Coburn into nonprofit horse care: a 50,000-horse-long pee line. That’s the odd name for a controversial practice. Coburn explains that pregnant mares excrete a hormone in their urine that can be readily absorbed by humans. “There are pharmaceutical companies who buy the urine from farmers who collect it,” she says. The companies extract the hormone from PMU (pregnant mare urine) and put it in hormone replacement therapy drugs.