Cortisol in Saliva, Urine, Feces, and Hair as Non- and Minimally Invasive Measures of Adrenocortical Activity in Intensively Housed Pigs

Abstract

Blood cortisol measurements may be confounded by sampling-induced handling and restraint, motivating the use of alternative matrices to assess adrenocortical activity in pigs. This narrative review examines the physiological time windows, collection requirements, analytical validation, and interpretive limitations of saliva, urine, feces, and hair. Saliva captures rapid responses but remains sensitive to collection conditions; urine integrates secretion over bladder filling and requires dilution correction; fecal glucocorticoid metabolites reflect delayed, integrated excretion and require a species-appropriate assay. Hair offers a potentially longer integration window, but controlled validation in pigs remains inconsistent, and clipping generally requires brief restraint. Antibody specificity, sample processing, and normalization constrain comparisons between studies. Published concentration benchmarks should not be interpreted as validated, production-stage-specific reference intervals. The practical matrix-selection framework presented here rests primarily on cross-study inference rather than direct comparisons of all four matrices under a common challenge. Cortisol indicates adrenocortical activation without establishing its cause or emotional valence. Interpretation therefore requires complementary behavioral, clinical, and production measures. A minimum reporting standard and priorities for paired-matrix validation, standardized sampling, and category-specific reference intervals are proposed. These matrices support comparative monitoring; none should be treated as a standalone diagnostic test of compromised welfare.