Poop scoopers at the St. Louis Zoo deliver droppings to scientists who study the hormonal health of animals — from fertility to stress levels.

Feces contains hormones that are excreted through the body’s filtering process. Those hormones also pass through blood, saliva, urine and hair, but who wants to take that from a rhinoceros?

“Poop is just the easiest to collect. Keepers are cleaning it up every day,” said Corinne Kozlowski, lead endocrinologist (hormone researcher) at the zoo.

The St. Louis Zoo’s endocrinology lab has tested 42,000 stool samples in 20 years of operation. The samples from 60-plus animal species have come from more than 150 zoos and other organizations around the country. Only two other zoos — the National Zoo in Washington and the Brookfield Zoo near Chicago — accept outside fecal samples for testing.

Kozlowski and her team track mammals’ estrogen, progesterone and testosterone levels as well as cortisol, a stress hormone. Zookeepers follow the ovulation cycles of females so they can encourage (or discourage) the mating process. The lab can make a pregnancy diagnosis, tell if contraception is working or figure out if an animal is infertile. They track hormones during pregnancy so caretakers know when to prepare for an impending birth.