Integrating Reference Intervals into Our Welfare Monitoring Toolkit

There are many ways that we humans assess and track our health and well-being. Many of us have had blood tests ordered to gain more information about our physical health. So, how do our doctors determine if blood values fall within a normal, healthy range? When you receive your results, you may notice reference intervals (with a low value and a high value) that help you interpret your numbers. This range is developed by considering the values of healthy adults and may vary based on sex or age. If your values fall outside of the normal range, you’ll likely discuss a course of action with your doctor. You may begin a treatment plan or start taking medication. Perhaps the doctor will recommend that you see a specialist or undergo further testing.

As our Animal Welfare Research Team described in a previous blog, CZS can integrate reference intervals into our “toolkit” for monitoring the health and well-being of individual animals. In other words, aside from observing behavior and performing physical exams, we can compare an individual’s value for a particular measure to the normal range for healthy individuals of that species. In fact, we can create reference intervals for measures other than blood variables. We can create reference intervals for physiological biomarkers that can be tracked via non-invasive sample types (e.g. collecting fecal samples to monitor fecal glucocorticoid metabolites or fecal immunoglobulin-A). We can even create reference intervals for behaviors!

In 2016, we initiated a study to examine chimpanzee welfare, which allowed us to create reference intervals for this species. Specifically, we analyzed data from 40 subjects housed across 16 zoos accredited by the Association of Zoos and Aquariums to generate reference intervals for both behavioral measures (e.g. social play, manipulating enrichment) and physiological measures (fecal glucocorticoid metabolites, fecal immunoglobulin-A). We discovered that most of these measures did not vary by age or sex. However, we found that the proportion of time spent engaged in mutual social grooming (i.e. when two or more individuals groom each other at the same time) decreased as chimps aged. Furthermore, as compared to females, males: 1) spent a higher proportion of time performing aggressive contact behaviors and displaying to other chimps, and 2) performed sexual examination behaviors at a higher rate. We published these findings in the journal Animals (special issue: Advances in Chimpanzee Welfare).

In the future, veterinarians, welfare scientists, and animal care professionals can use reference intervals as a diagnostic tool that can be integrated into health and welfare assessments. Individuals can be “flagged” if a value falls outside of the expected range. If this occurs, the animal care team can discuss next steps for investigating this concern, just as your doctor would. For example, we might collect additional data or introduce a change to the environment/husbandry routine in an attempt to “move” the value into the expected range. Ultimately, we can use reference interval data to make evidence-based decisions, gaining insight into how various management practices and environmental conditions impact welfare.
Dr. Jessica Whitham
Animal Welfare Biologist
Published July 11, 2023