Title: Repeated mixing and isolation: Measuring chronic, intermittent stress in Holstein calves
Authors: Wilcox CS, Schutz MM, Rostagno MR, Lay DC Jr, Eicher SD
Journal: J Dairy Sci
Accepted date: 2013 Jul 20
Interpretive summary: During chronic stress, glucose production in response to stress hormones is not sufficient to support glucose demand. This is evidenced by increased blood glucose in calves after transport. In animal well-being studies, determining glucose consumption may be a non-invasive way to substantiate that stress was induced. Molasses is an energy dense food (glucose source). To study whether a drive to replace glucose by molasses consumption would occur with chronically stressed calves, calves were socially stressed by a day of isolation followed by regrouping with new calves. Control calves were housed singly, but with tactile, auditory, and visual access to other calves. The traditional measure of stress, increased cortisol (stress hormone), was detected over the entire period. After a challenge to determine if the calves were chronically stressed (ACTH challenge), cortisol concentrations were dramatically increased in the control calves and low in the stressed calves. This showed that stressed calves’ ability to respond had been suppressed, a sign of chronic stress. Change from negative to positive for fecal shedding of Salmonella was much greater at the first move than in succeeding moves. This suggests that the calves had habituated to some degree to the moves. Additionally, behavior was changed by the stressor. Stressed calves spent more time standing, took longer to lie down, and consumed more molasses (all suggesting an activated state) than control calves. However, after the ACTH challenge, control calves became more active for the first 4 h following the injection than stressed calves, but were less active by the afternoon observation. This illustrated that control calves were more affected by the ACTH challenge, and stressed calves could not respond to the ACTH stimulus. Together, these results demonstrated that a chronic stress condition was reached within a 2-wk period and that increased molasses consumption by dairy calves can be used to confirm that a social stress condition has occurred.
Publication date: 2013 Nov