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Hair may be a useful matrix to detect cumulative cortisol concentrations in studies of animal welfare and chronic stress. The aim of this study was to validate a protocol for cortisol detection in hair from dairy cattle by enzyme immunoassay (EIA). Seventeen adult Holstein-Friesian dairy cows were used during the milking period. Hair cortisol concentration was assessed in 25-day-old hair samples taken from the frontal region of the head, analysing black and white coloured hair separately. Concentrations of cortisol metabolites were determined in faeces collected twice a week during the same period of time. There was a high correlation between cortisol values in faeces and cortisol in white colour hair samples but such correlation was not significant with the black colour hair samples. The intra-and inter-assay coefficients of variation were 4.9% and 10.6%, respectively. The linearity showed R 2 = 0.98 and mean percentage error of −10.8 ± 1.55%. The extraction efficiency was 89.0 ± 23.52% and the parallelism test showed similar slopes. Cortisol detection in hair by using EIA seems to be a valid method to represent long-term circulating cortisol levels in dairy cattle.Keywords: animal welfare, cortisol, dairy cattle, EIA, hair ImplicationsThe main implication of this study is the validation of a methodology for hair cortisol detection by enzyme immunoassay in dairy cattle. Hair cortisol detection is a promising methodology able to give information on long-term retrospective cortisol levels, which cannot be provided by any other established matrix. This study opens the possibility to use this methodology in chronic stress studies in dairy cattle welfare research, which is nowadays a hot topic.

The measure of corticosterone (CORT) in feathers has been recently recognized as a valid and easily obtainable measure of chronic glucocorticoids secretion in avian species. This measure provides meaningful interpretations of how individuals respond to environmental perturbations. The growing interest of the public toward animal-food production welfare shows the need for improving and expanding objective tools to evaluate this issue. The present study evaluates whether it is possible to detect CORT in broiler feathers, and thus, assess if it would be a useful measure to study broiler welfare. Twenty-two broilers were randomly selected from an intensive farm. Four to 6 dorsal feathers were collected from each bird, and sex, weight, and morphological aspects of feather status were recorded. We tested the feasibility for detecting CORT in broiler feathers by ELISA, which had never been done before, and an assay validation test was performed. No significant relationships were found between feather CORT concentrations and physiological variables such as sex, weight, and fault bars in broilers. To our knowledge, this is the first study that uses broiler feathers as a matrix that provides a retrospective record of their hypothalamic-pituitary-adrenal activity. Results indicate that ELISA is a valid tool to detect feather CORT levels in broilers.

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