Timing Animal Reproductive Cycles

Succesful Sichuan takin breeding at Lincoln Park Zoo was boosted by surveys of the species' reproductive hormones.

Using Hormones to Help Breeding

Every species has its own unique reproductive cycle, dependent on biology and environment. Some animals are seasonal breeders; others can mate year round. Some species require specific foods, light cycles or behavioral prompts to mate, and estrous time, gestational period and duration between births can all vary.

Zoos are very careful to make the right matches to ensure the long-term health of the populations in their care. But how to know if animals are fertile, mature, receptive or ready for breeding?

Hormones can help. By measuring testosterone, estrogen and progesterone over time—the same hormones that guide reproduction in humans—endocrinologists can gain insight into animal reproductive cycles. This can provide valuable insight for ensuring baseline health and choosing the right time to introduce potential partners.

Most reproductive hormone measurements, at the zoo and in the wild, come from non-invasive fecal samples. Reproductive research projects can harness an abundant resource without bothering the animals, gathering valuable information to improve conservation and care.


Rachel Santymire, Ph.D., is director of Lincoln Park Zoo's Davee Center for Epidemiology and Endocrinology

Rachel Santymire, Ph.D.
Director, Davee Center for Epidemiology and Endocrinology

Katie Fowler, M.S. is an endocrinology laboratory associate in Lincoln Park Zoo’s Davee Center for Epidemiology and Endocrinology.

Katie Fowler
Endocrinology Laboratory Associate


Michelle Rafacz, Ph.D., is an adjunct scientist with Lincoln Park Zoo's Davee Center for Epidemiology and Endocrinology

Michelle Rafacz, Ph.D.
Adjunct Scientist

Jennifer Howell-Stephens, Ph.D.
Adjunct Scientist

Learn More

Fecal sample storage boxes at Lincoln Park Zoo's Davee Center for Endocrinology and Epidemiology  

Where Does All the Poop Go?
Not all of the poop produced by the zoo’s animals gets pitched. Fecal samples are also repurposed for hormonal analysis.


Hormone Detectives
Studying the hormones of animals can inform a wide array of researchers' decisions, including breeding, stress and introductions. Learn more about this vital information here.