Exploring immunoglobulin A as a stress biomarker in lions (Panthera leo): Validation of an immunoassay for its measurement in feces

Immunoglobulin A (IgA) has been investigated as a stress biomarker with the potential to complement glucocorticoid measurements in welfare assessments. This study aimed to develop the methodology and validate an enzyme immunoassay (EIA) for quantifying IgA in feces (FIgA) of lions (Panthera leo), investigate excretion patterns of FIgA under baseline conditions in captive lions, and explore its relationship with fecal glucocorticoid metabolites (FGM). Feces were collected from 11 lions housed in stable social groups at four Spanish zoos over a period of two to six weeks. FIgA was reliably quantified using a commercial EIA, with concentrations ranging from 0.28 to 794.17 μg IgA/g feces, showing substantial intra- and inter-individual variability. Females had significantly higher FIgA concentrations than males (113.10 vs 54.96 μg IgA/g feces; p < 0.01). Additionally, FIgA concentrations varied across zoos (p < 0.001). Positive correlations were found between FIgA and FGM for all samples combined (rho = 0.43, p < 0.001) and across individual means (rho = 0.70, p < 0.05), but not consistently when examining each lion separately. This study demonstrates for the first time that IgA can be reliably quantified in lion feces, paving the way for its application in welfare studies.