Hair cortisol concentration in postpartum dairy cows and its association with parameters of milk production

Hair cortisol concentration (HCC) is considered as an indicator for a minimally invasive assessment of long-term stress. In dairy cows, in addition to stress influences, changing physiological conditions during gestation and lactation (eg, due to varying energy requirements or fluctuating milk yield) may affect HCCs. Thus, the aim of our study was to investigate HCCs of dairy cows during different stages of lactation and to determine the relationship between milk production traits and hair cortisol levels. Samples of natural hair and regrown hair were collected from 41 multiparous Holstein Friesian cows at 100-d intervals from parturition to 300 d postpartum. All samples were analyzed for cortisol concentration and the association of HCC with milk productions traits was evaluated. Our results show that cortisol concentration in natural hair increased after parturition and was highest 200 d postpartum. Cumulative milk yield from parturition to 300 d showed moderate and positive correlation with HCC in natural hair at 300 d. There was a positive correlation between urea concentration in milk and cortisol levels in regrown hair at 200 d, and between somatic cell count in milk and HCC in natural and regrown hairs 200 d postpartum. Together, these findings suggest that physiological loads during lactation, eg, caused by metabolic stress and/or inflammation, may be associated with increased HCC levels. In addition, the results on hair color confirm previous findings in cattle that black hair has higher cortisol concentrations than white hair. Black hair therefore appears to be more suitable for hair cortisol analysis as it provides higher protection against photodegradation.

The dark side of white hair? Artificial light irradiation reduces cortisol concentrations in white but not black hairs of cattle and pigs

Analysing hair cortisol concentrations (HCCs) is a minimally invasive way to retrospectively assess long-term stress, and its application in studies of animal welfare and stress has attracted considerable interest. However, not only stress-related effects but also hair-specific characteristics and external influences can affect HCCs and interfere with the interpretation of results. Thus, it was the aim of this study to investigate the impact of daylight and UV irradiation on cortisol concentrations in the hairs of pigs and cattle. We also examined whether a potential irradiation effect on HCCs depended on the colour of the hair. For this purpose, black and white hair samples from 18 Saddleback pigs and 18 Holstein Friesian cattle were exposed to artificial light (both visible and UV) and compared with control hair samples from the same animals kept in the dark. Exposure to artificial light significantly decreased HCCs in both pigs (P < 0.05) and cattle (P < 0.001), and hair colour had an influence on HCCs, with black hair showing higher cortisol levels than white hair (cattle: P < 0.001, pigs: P = 0.07). The interaction between light exposure and hair colour was significant in both pigs (P < 0.01) and cattle (P < 0.001), so light exposure reduced HCCs in porcine white hair but not black hair. In cattle, light-exposed white hair exhibited lower hair cortisol levels than control white hair or black hair. These results demonstrate that artificial light irradiation degrades hair cortisol or favours its elimination by structural changes of the hair matrix. However, this effect was only detectable in white hair, indicating that the melanin pigments in black hair absorbed radiation, thereby reducing the effects of photodegradation. Compared with other known influencing factors on HCCs, such as age and body region, the influence of light irradiation was relatively low in this in vitro experiment. However, further studies should investigate this influence under real-life animal conditions, such as outdoor and indoor housing.

Is it getting in the hair? - Cortisol concentrations in native, regrown and segmented hairs of cattle and pigs after repeated ACTH administrations

Adrenocorticotropic hormone (ACTH) is part of the hypothalamic-pituitary-adrenal axis response to stress and induces the release of cortisol, which is commonly used as an indicator in stress and animal welfare research. In recent years, hair cortisol concentration (HCC) gained increasing importance as a promising retrospective indicator for stress in animals. Thus, the aim of our study was to validate HCC as a potential indicator of increased endogenous cortisol release in cattle and pigs by repeated ACTH administrations followed by cortisol analysis in different hair types. For this purpose, 34 cattle and 38 gilts were treated either with repeated i.m. injections of ACTH or saline every second day over a period of 4 weeks. Saliva samples were taken before and after injections once a week from selected animals to verify the endogenous cortisol response. At the end of the treatment (week 4) and after 8 and 12 weeks, samples of natural and regrown hair were taken from the caudo-dorsal region of the back and analyzed for cortisol concentrations. In addition, natural hair was sampled after 12 weeks and cut into segments prior to analysis. Treatment with ACTH revealed a significant increase in salivary cortisol after application in both species, although this increase was attenuated in pigs compared to cattle. In week 4, HCCs were significantly elevated in natural and regrown hair of ACTH-treated animals. In cattle, HCCs significantly increased after ACTH treatment in natural, regrown and segmental hair compared with control animals, indicating that HCC may be a promising indicator of stress, as cortisol levels in all hair types reflected the preceding period with increased cortisol release. In pigs, there were no differences in HCCs between treatments. This may be caused by the lower systemic cortisol response in pigs, but seasonally reduced hair growth and external cross-contamination of hair by saliva and urine under commercial husbandry conditions may also interfere with the validity of HCC in this species.

It's getting hairy - External contamination may affect the validity of hair cortisol as an indicator of stress in pigs and cattle

Hair cortisol concentration (HCC) is increasingly used for the assessment of enhanced hypothalamic-pituitary-adrenal (HPA) axis activity, e.g., caused by repeated or long-term stressful conditions or pathologies. However, there is still a lack of knowledge regarding the mechanisms and sources of cortisol incorporation into the hair and possible confounding factors, especially in non-human animals. Farm animals are usually kept under confined housing conditions, have close contact with each other and with soiled environments and may thus be exposed to contamination with urine, feces and saliva, which are known to contain substantial concentrations of cortisol or its metabolites. Therefore, the aim of our study was to investigate the impact of contamination with urine, feces and saliva on the cortisol concentration in the hair of pigs and cattle. In an in vitro experiment, hair strands of 12 pigs and 12 cattle were repeatedly contaminated with urine and saliva, containing either low or high cortisol concentrations, or with the feces of the respective species and were compared with hair treated with water or untreated hair. Contamination was performed over 20 days for two hours daily. Thereafter, all samples were washed, ground, extracted and analyzed for HCCs following the same protocol. Our results showed that contamination with urine caused a considerable and concentration-dependent increase in HCCs in both species. Saliva had a comparable effect only in cattle. In addition, the treatment with water led to a reduction in the cortisol concentration of porcine hair, whereas contamination with feces caused an increase in HCC only in cattle. Our findings provide evidence that contamination of hair with cortisol-containing body fluids causes incorporation of cortisol into the hair shaft, probably via diffusion depending on the concentration gradient. In that case, cortisol in hair derived from contamination cannot be distinguished from cortisol originating from blood. Thus, contamination may affect the validity of hair cortisol as an indicator of HPA axis activity and cannot be prevented by decontamination protocols prior to analysis.

Within a hair's breadth - Factors influencing hair cortisol levels in pigs and cattle

During the last two decades, hair cortisol concentration (HCC) has proven to be a promising marker for the evaluation of increased hypothalamic-pituitary-adrenal axis activity caused by repeated or long-term stressful conditions. A minimally invasive sampling procedure, simple storage and the retrospective characteristic of one hair sample are reasons why HCC is increasingly used not only in human medicine but also in animal welfare research. However, before applying HCC as a reliable indicator for stress, it is important to investigate potential influencing factors in addition to stressors in the species of interest. Thus, the aim of our study was to elucidate the impact of age, sex, hair color, body region, age of hair segments and season of hair sampling on HCC in pigs and cattle. Hair samples were taken by electric clippers and analyzed by ELISA after extraction. Our results show similar effects of influencing factors in both species. Significantly increased HCCs were found in young animals after birth compared with older age groups. In addition, HCCs were significantly higher in samples obtained from the tail tip in comparison with samples from the shoulder, neck and back regions, in black hair compared with white hair and in distal hair segments. Season had an impact on HCC only in cattle, which exhibited higher levels in winter than in summer. In conclusion, age, body region, hair color, hair segment and season affect hair cortisol concentrations and should be considered and controlled for when HCC is applied as a potential stress indicator in pigs and cattle. In addition, further research is necessary to elucidate the mechanisms by which cortisol is incorporated into the hair shaft.

The use of hair cortisol for the assessment of stress in animals

The hair cortisol concentration (HCC) is assumed to be a retrospective marker of integrated cortisol secretion and stress over longer periods of time. Its quantification is increasingly used in psychoneuroendocrinological studies in humans, but also in animal stress and welfare research. The measurement of HCCs for the assessment of stress offers many considerable benefits for use in domesticated and wild animals, especially due to the easy and minimally invasive sampling procedure and the representation of longer time periods in one sample. This review aims to outline the different fields of application and to assess the applicability and validity of HCC as an indicator for chronic stress or long-term activity of the hypothalamic-pituitary-adrenal axis in wild and domesticated animals. Specific hair characteristics are presented and the advantages and limitations of using HCC are discussed. An overview of findings on the impact of stress- and health-related factors on HCCs and of diverse influencing factors causing variation in hair cortisol levels in different species is given. Recommendations for the use of hair cortisol analysis are proposed and potential fields of future research are pointed out. The studies indicate an effect of age and pregnancy on HCCs, and cortisol incorporation into hair was also found to depend on hair colour, body region, sex and season of year, but these results are less consistent. Furthermore, the results in animals show that a wide array of stressors and pathological conditions alters the cortisol concentrations in hair and that HCC thereby provides a reliable and valid reflection of long-term cortisol secretion in many species. However, more research is necessary to investigate the underlying mechanisms of cortisol incorporation into the hair and to explore the hair growth characteristics in the species of interest. To overcome confounding influences, the use of standardized sampling protocols is strongly advised.