Effects of simulated environmental conditions on glucocorticoid metabolite measurements in white-tailed deer feces

Environmental conditions may influence fecal glucocorticoid metabolite measurements if feces cannot be collected immediately after deposition. To evaluate the influence of environmental conditions on fecal glucocorticoid metabolite concentrations, we exposed fresh fecal samples to 1 of 5 simulated conditions: (1) room temperature (22°C), (2) high heat (38°C), (3) alternating high heat and room temperature cycle, (4) alternating freezing (-20°C) and room temperature cycle, and (5) simulated rainfall (0.85 cm every other day at 22°C) for 7 days. We collected fresh white-tailed deer (Odocoileus virginianus) feces at various times pre- and post-adrenocorticotropin injection to provide samples with initially low (n = 5), medium (n = 5), and high (n = 5) glucocorticoid concentrations. Feces were mixed thoroughly and then allocated into five 10-g samples. Also, a 5-g sub-sample was taken from each fecal mass prior to treatment and stored at -20°C until assayed. We subsampled from all treatments once every 24-h for 7 days. Fecal samples were assayed using [¹²⁵I]corticosterone radioimmunoassay kits. Fecal glucocorticoid metabolites in all three groups in the simulated rainfall treatment and the low group in the alternating freezing and room temperature treatment increased significantly over the 7-day period. We believe increased microbial metabolism of fecal glucocorticoids may partly explain these results. Other biochemical processes (e.g., cleavage of conjugate side groups from hormone metabolites by non-microbial action or release of glucocorticoids from lipid micelles) may also have increased fecal glucocorticoid measurements. Our findings suggest that fecal samples exposed to rainfall for one week may artificially inflate fecal glucocorticoid measurements. Thus, researchers should recognize the potential bias when collecting fecal samples exposed to rainfall. Non-fresh samples may prove useful when care is taken to address the elevation in immunoreactive glucocorticoid concentrations.