Effect of repeated HPA axis stimulation on hair cortisol concentration, growth, and behavior in preweaned dairy cattle

Authors: KERN, JESSICA - Purdue University; JORGENSEN, MATTHEW - US Department Of Agriculture (USDA); BOERMAN, JACQUELYN - Purdue University; ERASMUS, MARISA - Purdue University; Johnson, Jay; Pempek, Jessica

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2024
Publication Date: 6/20/2024
Citation: Kern, J., Jorgensen, M.W., Boerman, J.P., Erasmus, M., Johnson, J.S., Pempek, J.A. 2024. Effect of repeated HPA axis stimulation on hair cortisol concentration, growth, and behavior in preweaned dairy cattle. Journal of Animal Science. https://doi.org/10.1093/jas/skae171.
DOI: https://doi.org/10.1093/jas/skae171

Interpretive Summary: Measures to quantify long-term or chronic stress in livestock are limited. The amount of cortisol (a stress hormone) deposited in the hair has been used as a non-invasive measure of long-term stress in some livestock species; however, few studies have investigated its use in young dairy calves. The objective of this study was to determine the efficacy of hair cortisol as a measure of stress in calves. Calves were injected (or not) with a hormone (Cosyntropin) that activates the stress response system at different frequencies during the first 2 months of life. Cosyntropin injection increased salivary cortisol concentrations (an indicator of acute stress) but did not increase hair cortisol concentrations. Body weight at weaning was lower for calves that received frequent injections of Cosyntropin compared to the control (saline) treatment. Calf behavior was similar between treatment groups. It can be concluded that the method used to activate the stress response system was sufficient to induce an acute but not chronic stress response in calves, and more research is needed to develop measures of chronic stress in young dairy calves.

Technical Abstract: The efficacy of utilizing hair cortisol as a non-invasive measurement to quantify chronic stress has been demonstrated in adult cattle, yet little research has explored this measure in calves. The study objective was to investigate the effects of repeated HPA axis stimulation using synthetic adrenocorticotropin hormone (Cosyntropin) intramuscular (IM) injections on hair cortisol concentrations, growth, and behavior in preweaned dairy calves. Twenty-seven Holstein calves were assigned to nine triads (based on sex and birth order) and randomly assigned to 1 of 3 treatments: 1) control (CON; 2 mL saline weekly); 2) moderate (MOD; alternating Cosyntropin [2 mcg/kg body weight (BW)] and saline weekly); or 3) frequent (FREQ; Cosyntropin [2 mcg/kg BW] weekly). Calves received their first injection on d 0 of the study (7 ± 1 d of age). An initial hair sample was collected from the tail switch between d -5 and -3, and subsequent hair samples were collected on d 21 and 49 of the study. Saliva was collected on d 0, 14, 28, and 42 immediately before injection and every 15 min for 2 h after injection to analyze for salivary cortisol concentrations. Calves were fitted with 3-dimensional accelerometers to continuously monitor lying time prior to the first injection, and accelerometers were removed on d 49. Growth measures (BW, hip height, hip width) were recorded weekly on injection days (every 7 days). Data were analyzed using repeated measures ANOVA (SAS 9.4). Models included the fixed effects of treatment, study day, and interaction between treatment and study day. The temperature humidity index (THI) was calculated using data from a weather station 1 km north of the dairy, averaged for the week prior to each injection, and included as a continuous covariate. Body weight was similar across treatments (CON [57.10 ± 1.07 kg], MOD [55.71 ± 1.11 kg], and FREQ [54.98 ± 1.10 kg]; P = 0.44). However, there was a negative association between BW and THI (P = 0.03). There was an effect of treatment (CON [1.30 ± 0.04 ng/mL], MOD [2.08 ± 0.04 ng/mL], and FREQ [2.16 ± 0.04 ng/mL]; P <0.01) on salivary cortisol concentrations. Additionally, there was a significant interaction between treatment and timepoint (P < 0.01). However, THI (P = 0.11) did not significantly affect salivary cortisol concentrations. There was no effect of treatment on hair cortisol concentrations, but concentrations decreased from d21 (1.28 ± 0.02 ng/ml) to d49 (0.93 ± 0.02 ng/ml; P < 0.01). Treatment did not influence average daily lying time (CON [18.5 ± 0.23 h/d], MOD [18.6 ± 0.23 h/d], and FREQ [18.5 ± 0.23 h/d]; P = 0.96). These results indicate that repeated HPA axis stimulation, through Cosyntropin administration, did increase salivary cortisol concentration with an effect of time but did not influence hair cortisol concentration, growth, or behavior between treatments.