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Title: Effect of repeated HPA axis stimulation on hair cortisol concentration, growth, and behavior in preweaned dairy cattle.
Author: Kern J, Jorgensen MW, Boerman JP, Erasmus M, Johnson JS, Pempek JA.
Journal: J Anim Sci; 2024 Jan 03; 102():. PubMed ID: 38898575.
Abstract:
The study objective was to investigate the effect of repeated hypothalamic-pituitary-adrenal (HPA) axis stimulation using synthetic adrenocorticotropic hormone (ACTH) intramuscular injections on hair cortisol concentration, 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 study day 0 (7 ± 1 d of age). Hair was collected from the tail switch between days -5 and -3 (baseline), 21, and 49 and analyzed for cortisol concentration. To verify the endogenous cortisol release by Cosyntropin during the treatment period, saliva was collected on days 0, 14, 28, and 42 before injection and every 15 min for 2 h after injection for analysis of salivary cortisol concentration. Calves were fitted with accelerometers to continuously monitor lying time, number of lying bouts, and lying bout duration throughout the study. Growth measures (BW, hip height, hip width) were recorded weekly. Data were analyzed using repeated measures ANOVA (SAS, Version 9.4), and models included the fixed effects of treatment, time (min or study day), and interaction between treatment and time. Temperature humidity index was included as a continuous covariate in all models. We observed a treatment × min interaction (P < 0.0001), whereby salivary cortisol concentration was lower in CON calves compared to MOD and FREQ calves 15 to 120 min postinjection. While hair cortisol concentration was not influenced by treatment, concentration decreased from day 21 (1.28 ± 0.03 ng/mL) to 49 (0.93 ± 0.03 ng/mL). Average BW was similar across treatments (CON [59.4 ± 1.09 kg], MOD [58.6 ± 0.98 kg], and FREQ [57.6 ± 0.96 kg]; P = 0.50). There was no evidence to suggest a difference in 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 = 0.99). These results suggest that repeated HPA axis stimulation through Cosyntropin administration increased salivary cortisol concentration, but did not influence hair cortisol concentration, growth, or behavior in preweaned dairy calves. 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 noninvasive 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 less invasive measure of stress in calves. Calves were either injected with saline (control) or Cosyntropin, a hormone that activates the stress response system, at different frequencies during the first two months of life. Cosyntropin injection increased salivary cortisol concentration (an indicator of acute stress) but did not increase hair cortisol concentration. There was no evidence to suggest a significant effect of treatment on calf growth. Calf behavior was similar between treatment groups. These results suggest that the method used to activate the stress response system in this study was sufficient to induce an acute stress response in calves (as indicated by increased salivary cortisol concentration), and more research is needed to investigate measures of chronic stress in young dairy calves.

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