Studies in a wide range of species1-5,7 have shown that the stress hormone cortisol can be measured in hair samples.  Furthermore, since it has been proven cortisol is deposited in hair as the hair grows, hair cortisol levels can provide information on chronic or long term stress levels that may not be observable in the relative snap-shot provided by fecal or blood samples.   Indeed, depending up the length of the hair and the rate of hair growth, it may be possible to section hair and look at stress levels in specific periods or seasons as well.

There are some complicating factors that will need to be considered.  Deposition of cortisol within the hair may vary both with the location of the hair on the body and with the color of the hair sampled1,4,6,7, so consistency in sample collection is vital. It is also important to consider the question of whether the stressing factor being studied is chronic or acute, and when, relative to hair collection, the event occurred.    If the stressing event was truly acute and short term,  like the capture and transport of an animal over the course of 1 day for immediate relocation for release, the overall difference in cortisol deposited within the hair may not be significant enough to be reliably discerned if the entire length of the hair is being used as the sample.  Additionally, if the stress event is further in the past than the growth and shed rate of the hair being sampled it may be missed.  An example of this is a subject with a chronic disease, where the most recent flare-up occurred too far back in time to be observed in short or frequently shed hair samples causing the diseased and control animals to have similar cortisol levels. Cortisol is also water soluble, and hair that is subject to frequent washing may have lower cortisol levels than samples from hair that has not been washed as often.  How the hair sample is collected may impact what information can be obtained.   Collecting the entire hair, along with at least a portion of the root is typically preferred.   This gives you a better timeline – if you have the root or a portion of the root then you have essentially a time zero on the day of collection with the length of the hair stretching back into the past.  This ensures recent events will be included in your sample – but also, when combined with the rate of hair growth for the species in question, allows you to section longer hair samples and look at trends over time within one individual.  If it is not practical to collect samples with at least part of the root attached and the hair sample is to be cut, care should be taken to consistently cut the hair as close to the skin as possible especially if you plan to compare results across different animals.

Ultimately the question of whether or not hair samples are a good option for a particular study depend upon the goals of the study.   Hair samples are non-invasive and relatively easy to obtain from animals habituated to human contact.   They can provide good insight long term into the overall stress of an individual or group which can be helpful for disease monitoring, husbandry/herd management, or examining the stress of captive living environments.   However, for monitoring acute or episodic stress events, other sample types such as feces or urine might provide better data.

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  1. Accorsi et al. (2008) Cortisol determination in hair and faeces from domestic cats and dogs; Gen Comp. Endocrinol., 155 398
  2. Amador et al. (1993) Deficient testicular and adrenal steroidogenesis in mutant cream (e/e) Syrian hamsters; Esp. Fisiol. 49 175
  3. Raul et al. (2004) Detection of physiological concentrations of cortisol and cortisone in human hair; Clin, Biochem., 37 1105
  4. Sotohira et al. (2017) Stress assessment using hair cortisol in kangaroos affected by lumpy jaw disease; Vet. Med. Sci. 79 852
  5. Veronesi et al. (2015) Coat and claws as new matrices for noninvasive long-term cortisol assessment in dogs from birth up to 30 days of age; Theriogenology, 84 791
  6. Bennett and Hayssen (2010) Measuring cortisol in hair and salica from dogs: coat color and pigment differences; Domest. Anim. Endocrinol., 39 171
  7. Nejad et al. (2017) Coat and hair color: hair cortisol and serotonin levels in lactating Holstein cows under heat stress conditions; Anim. Sci. J. 88 190

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