Skip to main content


Endocrinology is the study of hormones—internal chemical messengers that regulate animal physiology and behavior. The Saint Louis Zoo's Endocrinology Lab works to conserve endangered species, both in zoos and in the wild, by studying a variety of hormones. Measuring levels and patterns of hormones provides insight into an animal's reproductive status and well-being, information that can be used to improve health and reproductive success.

Reproductive Status

During pregnancy, hormone levels rise after mating and remain elevated until delivery. By analyzing samples collected after mating, the Endocrinology Lab can diagnose pregnancy in a wide variety of species. Early diagnosis allows animal care staff to prepare for a birth by responding to the mother’s changing nutritional needs and by providing nesting material or a den. For pairs with a breeding recommendation, hormone measures can establish whether a female is having normal reproductive cycles and if she is capable of maintaining pregnancy. Hormone analysis can also help diagnose fertility problems and determine the age of puberty.


Animals often experience changes in their environment, such as being placed into a new habitat, or social group changes. When events like these occur, levels of the hormone cortisol can rise, an increase that leads to changes in the body that help animals adapt to their new surroundings. Cortisol measures provide a way to understand how animals cope with these experiences and help staff ease an individual’s transition, thereby supporting the animal’s well-being.

The Endocrinology program has developed and validated steroid assays for a wide array of species and sample types. In particular, the lab specializes in analyzing hormone levels in fecal, urine and saliva samples. These samples contain much of the same information as blood, with the added advantage of not having to disturb the animal during collection.

The Endocrinology Lab also provides diagnostic services to zoos, universities, wildlife agencies and conservation organizations at minimal cost.