Sifting through Poop

A tiger's poop can reveal a lot of information to researchers.

A tiger’s poop can reveal a lot of information to researchers.

I sift poop for a living. Well, that’s not quite true! I study hormones, those tiny chemical messengers that circulate in your body and control all sorts of amazing things, like when to grow or feel happy or sad, and, what I’m interested in, when to reproduce. Poop is just where I find the hormones. I could look for them in blood, just like your doctor might. But I work with animals, and they would rather you didn’t take their blood—anyone interested in getting close enough to a rhino or tiger to take a blood sample? Besides, blood only gives me a snapshot of their hormones at that moment when it’s collected. Hormones just don’t hang around in the blood very long. They do their job and are removed, often ending up in poop. In fact, hormones accumulate in the poop. When I measure the hormones found in poop, I get an average of what’s going on for that animal over the last 12 or more hours, not just a snapshot. And it’s easy to collect! So that’s the why, the how is bit more involved.

Every day the keeper collects a fresh sample in a small plastic cup, then freezes it, which stops bacteria and mold from growing, and prepares it for the next step. The sample is then freeze-dried, just like coffee. Freeze drying removes the water and makes the sample stable for long-term storage at room temperature. Next the sample is crushed and sifted. This removes the undigested material that interferes with the hormones during testing. A small amount of this dried and sifted material is weighed out and placed in a container with a liquid solvent. The hormones come off the poop and move into the solvent. This liquid is saved, and the rest is thrown away. I now have a liquid, or extract, containing the hormones I’m interested in.

Since hormones are too small to count directly, even with a microscope, a small portion of this extract is subjected to a special test called an immuno-assay. The assay involves combining the extract with a solution of specially labeled antibodies that attach to the hormone I’m testing. Once combined with these antibodies, the hormone that was too small to see or count becomes visible in a special detection machine. The detection machine counts the hormone-antibody couplets, and then it’s an easy calculation to determine the hormone level for each sample and each day. Graph the data, and you get a hormone profile revealing the reproductive status of each animal indicating if she is cycling, pregnant, or about to give birth. This information helps our animal care staff make informed decisions about how to care for and manage each animal.

Alan Fetter is a laboratory manager for the San Diego Zoo Institute for Conservation Research.