Evaluation of hair cortisol as a biomarker of chronic stress in beef cattle

Abstract Text: Three experiments were conducted to assess hair cortisol concentration as a biomarker of chronic stress in beef cattle. In Exp. 1, 24 calves (230.4 ± 13.0 kg BW) were randomly split into two groups immediately after weaning: half of them remained at the ranch of origin (OR), while the other half were transported to a feedlot (TF). Weight and hair samples were collected from all calves at the time of weaning and for a period of 30 d post weaning to determine performance and cortisol concentration. In Exp. 2, 24 calves (299.1 ± 28.2 kg BW) were randomly split in two treatments: no castration (CT) or band castration (BA). Weight and hair samples were collected from all calves at d 0, 35 and 63 after castration to determine performance and cortisol concentration. In Exp. 3, 160 crossbred steers (538 ± 36 kg BW) were used in a 84-d experiment with a randomized block design, to study the effects of wheat- (WH, 88.4% DM) or barley- (BA, 89% DM) based diets, or processing index (PI) of either 75% (PI75) or 85% (PI85) of their original volume-weight, on growth performance, stress and behavior of finishing beef cattle. Cattle were allocated to 16 feedlot pens (10 animals per pen, 4 pens per treatment), 8 of which were equipped with an automatic feed monitoring system. Flight speed, hair and saliva samples were collected on d 1, 28, 56 and 84 to determine behavior, acute and chronic stress. The TF group had a greater ADG (P < 0.01) and hair cortisol concentration (P = 0.05) than OR. There was a castration × time interaction (P < 0.05), where BA calves had greater hair cortisol and lower ADG than CT only at d 35 after castration. The PI75 treatment reduced (P = 0.05) DMI and increased (P = 0.04) feed efficiency. Cattle fed WH had greater hair cortisol (P = 0.01) and flight speed (P < 0.01) than those fed BA. There was a trend (P = 0.07) for a grain × PI interaction, where heifers fed WH-PI85 had lower salivary cortisol than those fed other treatments. Results indicate that hair cortisol can be used to assess chronic stress in beef cattle related to conditions associated with calf management at weaning, band castration or feeding management.

Keywords: Feedlot, stress, welfare