Cortisol concentration of regrown hair and hair from a previously unshorn area in dairy cows
Introduction
Hair cortisol concentration has evolved as a novel biomarker for chronic stress in humans (Meyer and Novak, 2012, Russell et al., 2012). Chronic stress caused by conditions such as chronic pain (Van Uum et al., 2008) in humans leads to increased cortisol concentrations in hair. During hair growth cortisol diffuses passively from the capillaries into the hair shaft (Pragst and Balikova, 2006) where it is stored (Wosu et al., 2013). Alternatively, cortisol may be incorporated into hair during keratinisation, or may be taken up by cells in the sebaceous glands and secreted onto emerging fibres in lipids (Burnard et al., 2017). Strenuous physical exercise may increase hair cortisol concentration in humans, and thorough washing of human hair treated with a hydrocortisone solution for 60 min did not reduce its cortisol concentration (Russell et al., 2014). There are conflicting reports on cortisol concentrations in predominantly catagen- and telegon-phase hair: One study described decreasing concentrations in human hair (Kirschbaum et al., 2008), whereas other studies in humans (Sharpley et al., 2010), dogs (Bennett and Hayssen, 2010) and rhesus monkeys (Davenport et al., 2006) did not. Studies on hair cortisol concentration also have been carried out in cattle (González-de-la-Vara et al., 2011, Comin et al., 2011, Comin et al., 2012, Comin et al., 2013, Peric et al., 2013, Burnett et al., 2014, Burnett et al., 2015) and showed that ill cattle have higher hair cortisol concentrations than healthy cattle (Comin et al., 2013, Burnett et al., 2015). An increase in hair cortisol concentration was seen on the day of parturition and three weeks postpartum compared with days 42 to 126 postpartum (Burnett et al., 2015). In another study, an increase occured 40 days after a change from winter indoor housing to summer grazing (Comin et al., 2011). Hair cortisol concentrations and the adrenal gland weights were recently investigated and compared in relation to the health status of slaughter cows. Chronically ill cows had significantly larger adrenal gland weights relative to body weight than acutely ill cows. Similarly, the hair cortisol concentration of chronically ill cows (1.37 pg/mg) was significantly greater than that of acutely ill cows (0.56 pg/mg). Furthermore, the total relative adrenal gland weight was positively and significantly correlated with hair cortisol concentration (Clavadetscher, 2016).
It is not known whether cortisol concentration differs between hair that has grown for one month and hair that has grown for several months. The growth rate of hair in Holstein cows depends on the area of the body and is 0.30 mm/day at the shoulder and 0.40 mm/day at the hip (Burnett et al., 2014). Determining whether the cortisol concentration of hair varies among samples obtained at different periods of hair growth is relevant because the technique is an important tool for substantiating stress in an animal. The primary goal of this study was to compare the cortisol concentration of hair that has grown for one month with that of hair from a previously unshorn area. A secondary goal was to investigate the effect of calendar month, pregnancy and illness on hair cortisol concentration.
Section snippets
Cows
The study was conducted during a one-year period (November 13, 2014 to November 12, 2015) and used 27 cows (16 Brown Swiss and 11 Swiss Fleckvieh). The cows were 3 to 17 years of age (mean ± SD = 6.6 ± 3.7 years) and produced 4400 to 7300 kg milk per lactation (5950 ± 832 kg). The cows were kept in a tie stall during the day and on pasture at night from April 28 to November 11. During the remainder of the year, they were turned out in a 460 m2 exercise yard with a concrete floor for approximately 4 h per
Hair cortisol concentration over the course of a year
The monthly mean hair cortisol concentrations of A samples ranged from 0.43 to 1.25 pg/mg and those of B samples from 0.53 to 1.04 pg/mg (Table 1). The overall mean hair cortisol concentration (mean ± sd) for A samples was 0.73 ± 0.46 pg/mg and the overall mean for B samples was 0.69 ± 0.45 pg/mg; this difference was not significant. There were significant differences in hair cortisol concentrations over time (F value A samples = 6.83, P < 0.01; F value B samples = 4.94, P < 0.01; Fig. 1, details in Table 1).
Discussion
The mean hair cortisol concentrations measured in A and B samples were considerably lower than values reported in other studies (2.5 pg/mg, Comin et al., 2011; 2.35 pg/mg, Moya et al., 2013; 5.7 pg/mg, Burnett et al., 2014; 12.15 pg/mg, González-de-la-Vara et al., 2011). Hair cortisol concentrations similar to those in the present study were recently measured in 142 slaughter cows, and possible reasons for the discrepancy among studies were discussed in detail (Clavadetscher, 2016). Methodical
Conclusions
Parturition in the month preceding sampling increased the cortisol concentration in hair that had regrown within one month after clipping.
Conflict of interest statement
The authors of this paper have no financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper.
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2020, Applied Animal ScienceCitation Excerpt :We prepared the hair samples by using a scissors to cut small fragments, which has been shown to produce significantly lower cortisol concentrations as compared with hair samples that were processed with a ball mill (Burnett et al., 2014). Similarly, to Braun et al. (2017), we believe that our measurement technique and hair preparation may have been linked to the observed differences in cortisol concentrations between this study and other studies. Further research should be performed to create methodology validation and establish baseline hair cortisol values.