Relationship between hair cortisol concentration and previous performance and feeding behavior in holstein bulls fed high-concentrate diets

Abstract Text: One main hormone produced during stress responses is cortisol. Hair can be used as matrix to measure cortisol levels in beef. Hair specimen could reflect average hormone levels over months and can be used to assess cortisol long-term variations. High cortisol concentrations stimulate breakdown of body tissues in order to release energy and protein to further support the stress response, and therefore it may impair animal growth. Thus, the hypothesis of the present study was that hair cortisol concentration should be negatively correlated with previous ADG, feed efficiency or feeding behavior parameters.Thirty-seven Holstein bulls (129 ± 2.9 kg BW and 110 ± 2.0 d age) housed in two pens were used to obtain hair samples (1 g) from the forehead by clipping. On 7 d hair was clipped to reflect the new cortisol incorporation in the following hair specimens, which were collected on days 120 and 216 of the study. The relationships between each previous performance and feeding behavior parameters and hair cortisol were evaluated by regression analyses using a fit model procedure of JMP® with animal as random effect. Hair cortisol concentration was positively correlated (P < 0.01) with ADG (r = 0.28), feed efficiency (r = 0.34), and coeficient of variation of concentrate intake (r = 0.36), whereas hair cortisol concentration was negatively correlated (P < 0.01) with average concentrate intake (r = - 0.37). Hair cortisol concentration tended (P = 0.10) to have a negative association with meal size (r = - 0.30), number of visits (r = - 0.16), and concentrate eating rate (r =- 0.21). In contrast to the hypothesis, the relationship between hair cortisol and ADG and feed efficiency was not negative. Incorporation of cortisol to the hair matrix assumes that blood-borne substances enter the hair through passive diffusion and subsequently become deposited in the hair shaft; however, other possible mechanisms of entry are proposed like the diffusion from sweat or sebum secretions. Probably, hair cortisol concentration needs to be greater to negatively impact ADG and feed efficiency. The negative relationship between meal size and eating rate and hair cortisol concentration may be related with its impact on digestive tract health. In conclusion, weak correlations were obtained between hair cortisol concentration with 3 mo previous data of performance and feeding behavior.

Keywords: bulls, hair cortisol, performance