Abstract
Hair cortisol is a novel biomarker of chronic stress. The objective of this study was to determine the effect of hair color and length, as well as, animal age on hair cortisol concentration in beef feedlot steers. Nineteen beef crossbred steers used for nutrition research and housed in a small feedlot setting were used for this study. Seven of the steers (680 ± 4.5 kg; ~9 years of age) were fitted with ruminal fistulas and duodenal cannulas. The other 12 steers (473 ± 3.1 kg; ~2.5 years of age) were fitted with only ruminal fistulas. Hair samples from each steer were collected throughout a period of 6 weeks from six different areas and analyzed for cortisol concentrations. One pre-determined area was shaved each week for 5 weeks (Weeks 1–5). During week 6, all five, previously shaved areas and an additional area was shaved to collect hair samples of various lengths. Hair length was recorded prior to the collection of each hair sample. Only data from the last week (Week 6) of collection were included in the analyses. Steers were categorized into one of three groups: old with black hair (OB, n = 3); old with white hair (OW, n = 3); young with black hair (YB, n = 12). Older steers exhibited greater hair cortisol concentrations than younger steers (P < 0.001). Hair cortisol concentration was not impacted by duration of growth (P = 0.33). Cortisol concentrations exhibited a weak, positive correlation with hair length (r = 0.33, P-value = 0.01). The average hair growth per week of beef steers in the winter months was calculated to be 0.90 mm. Further research should be performed to improve our understanding of the effect of hair characteristics, sampling methodologies and analysis techniques on hair cortisol concentrations.
Highlights
Physiological parameters are often used to quantify animal well-being
The combined impact of age and color had a significant impact on hair cortisol concentrations across periods of growth (P < 0.001), in relation to the different areas shaved in week 6 that were allowed various durations of growth (Figure 3)
A weak, positive correlation was observed between hair cortisol concentration and hair length (r = 0.33, P-value = 0.01) (Figure 4)
Summary
Cortisol is commonly measured to assess stress, whether acute or chronic, in many livestock species. This hormone can be measured using several different mediums—blood [1, 2], saliva [3, 4], urine [5], and feces [6]. These parameters provide an acute, time-point measurement of cortisol concentration [7, 8]. The measured cortisol concentration when using these methods, blood, can be affected by several factors, such as circadian rhythms [9], handling [10], restraint [11], and degree of habituation or acclimation [12].
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