Short communication: Factors affecting hair cortisol concentrations in lactating dairy cows

Abstract

Cortisol has long been used as a marker of the stress response in animals. Cortisol can be analyzed from different media, most notably from the blood, saliva, and feces; however, the collection of cortisol from some of these media requires invasive procedures or excessive handling of the animals. Furthermore, it is not possible to capture long-term increases in circulating concentrations of cortisol from the blood, saliva, or feces. Hair cortisol has been found to be a reliable alternative for measuring chronic stress. With this emerging measure, appropriate sampling methodology must be developed and validated. The aim of this study was to determine the effects of hair color, sampling location, and processing method on cortisol concentrations in hair from lactating black and white Holstein cows (n=18). Furthermore, we aimed to measure the hair growth rates at different body locations (n=12) and test hair cortisol levels when resampled over short intervals (n=37). Both black- and white-colored hair was collected from the shoulder, top line, hip, and tail switch of Holsteins; due to breed characteristics only white hair was harvested from the tail switch. All samples were cleaned with water and isopropanol, and then ground in a ball mill or finely cut with scissors once dry. Cortisol was extracted with methanol before being measured using a commercially available ELISA kit. Concentrations of cortisol were greater in white than in black hair (7.8 ± 1.1 vs. 3.8 ± 1.1 pg/mg). When only white samples were analyzed, hair from the tail switch had more cortisol than hair from the shoulder (11.0 ± 1.2 vs. 6.2 ± 1.2 pg/mg), whereas no difference was found when compared with the hip and top line. Samples ground with a ball mill had greater concentrations of cortisol extracted than those minced with scissors (10.4 ± 1.2 vs. 4.7 ± 1.2 pg/mg). The growth rate of hair was significantly greater at the tail switch compared with the hip and shoulder (0.51 ± 0.05 vs. 0.04 ± 0.05 vs. 0.03 ± 0.05 mm/d). When hair was collected every 3 wk after calving, a tendency was detected for multiparous cows to have greater concentrations of hair cortisol and significantly greater concentrations of cortisol on d 0 and 21 after calving compared with d 42, 84, and 126. In Holsteins, the hair on the tail switch is always white, grows more rapidly than other sites, and is sensitive enough to capture changes in cortisol over intervals as short as 3 wk, making it the ideal location for measuring hair cortisol.

Hair cortisol detection in dairy cattle by using EIA: protocol validation and correlation with faecal cortisol metabolites

“…The presence of higher cortisol concentrations in black samples in relation with the white ones is in concordance with studies that suggest that number of melanocytes and pigmentation favour the incorporation of lipophilic substances from the bloodstream into the hair (Pötsch et al, 1997;Pragst and Balikova, 2006). However, other studies found higher cortisol concentrations in white hair than in the black ones (González-de-la-Vara et al 2011;Cerri et al, 2012;Burnett et al, 2014). Our contradictory results may be because while the white hair samples were harvested only from the frontal region of the head, the black hair ones were a mixture of hair from frontal region of head and also from the occipital crest.…”

“…Thus, black hair samples were homogeneous in colour but not in location and so, hair type. The authors did not find any study comparing cortisol concentrations from these two close regions but other studies found differences in hair cortisol levels among other locations (Cerri et al, 2012;Moya et al, 2013;Burnett et al, 2014). Hair from the occipital crest in Holstein-Friesian cows is longer and thicker than hair from frontal region and studies performed by Burnett et al (2014) and Moya et al (2013) found higher cortisol concentrations in locations where hair type was also longer and thicker (especially the tail switch).…”

“…Hair from the occipital crest in Holstein-Friesian cows is longer and thicker than hair from frontal region and studies performed by Burnett et al (2014) and Moya et al (2013) found higher cortisol concentrations in locations where hair type was also longer and thicker (especially the tail switch). The growth rate and hormone accumulation or production rate could be different between types of hair (Moya et al, 2013;Burnett et al, 2014) and these differences could be the cause of the presence of higher cortisol levels in the heterogeneous black hair samples.…”

“…Although enzyme immunoassay (EIA) and ELISA methodologies have been used to detect hair cortisol in cows and beef (Cerri et al, 2012;Moya et al, 2013;Burnett et al, 2014), a complete validation of the methodology has only been done in beef cattle (Moya et al, 2013). Other studies have detected cortisol in hair from dairy cows using radioimmunoassay with validation tests (Comin et al, 2011 andGonzález-de-la-Vara et al, 2011).…”

Hair cortisol concentration and adrenal gland weight in healthy and ill cows

“…Hair cortisol concentration therefore has evolved as a novel biomarker for chronic stress in humans (Russel et al, 2012). There have been several studies on hair cortisol concentrations in healthy and ill cattle (González-de-la-Vara et al, 2011;Comin et al, 2011Comin et al, , 2012Comin et al, , 2013Peric et al, 2013;Burnett et al, 2014Burnett et al, , 2015; ill cattle have higher concentrations than healthy cattle Burnett et al, 2015). To the authors' knowledge, there have been no studies comparing adrenal gland weight and hair cortisol concentrations in cattle.…”