Suitability of saliva cortisol as a biomarker for hypothalamic–pituitary–adrenal axis activation assessment, effects of feeding actions, and immunostimulatory challenges in dairy cows1

Abstract

One of the most prominent physiological responses to stressors is the activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, currently assessed by measuring cortisol concentration in blood plasma. To reduce animal discomfort during sampling, which negatively affects stress biomarkers, current research focuses on noninvasive sampling of media other than blood, for example, saliva. The aim of this study was to assess the suitability of saliva cortisol as a biomarker under different physiological and immunological states in dairy cows. Our objectives were to 1) evaluate the relationship between HPA axis activation and saliva cortisol concentration, 2) investigate effects of some feeding action (as influenced by feed and water consumption) on saliva cortisol concentration, and 3) evaluate the time lag between plasma and saliva cortisol during induced inflammatory conditions by intramammary lipopolysaccharide (LPS) and lipoteichoic acid (LTA) injection. During a specific activation of the HPA axis, a positive correlation ( = 0.75, < 0.0001) between saliva and blood cortisol concentrations was observed with increased ( < 0.01) plasma cortisol concentrations following ACTH administration. Saliva and blood samples were taken before, during, and after drinking, feeding, and ruminating. Only a low correlation between saliva and plasma cortisol concentrations ( = 0.03, = 0.83) but no significant effects of the different feeding actions on saliva cortisol were observed. When compared with basal concentrations, cortisol concentrations in plasma significantly increased during inflammatory responses following LPS and LTA injection. Compared with plasma cortisol, changes in saliva cortisol concentrations occurred at a much lower level within a narrow range and did not necessarily follow changes in plasma. In conclusion, the positive correlation between saliva and plasma cortisol concentration in response to ACTH and inflammation suggests the suitability of saliva cortisol measurement for the HPA axis activation assessment. However, changes in saliva cortisol concentration occur within a very narrow range. Furthermore, not only must variation among individual animals be considered but also variation within the same animal. Only with additional knowledge of the concomitant physiological status of the cow it is possible to correctly evaluate saliva and blood cortisol samples.

Free and bound cortisol in plasma and saliva during ACTH challenge in dairy cows and horses

“…Our findings regarding the pattern of TC and free cortisol increasing after ACTH injection in horses are confirmed by earlier reports of Bousquet-Mélou et al (2006) and Peeters et al (2011). For dairy A c c e p t e d M a n u s c r i p t 13 cows, we observed a similar increase of TC concentrations during the ACTH challenge as described earlier (Yoshida and Nakao, 2005;Schwinn et al, 2016;Gross et al, 2017). The rising rFC demonstrates a greater increase of FC compared to TC, thereby confirming previous results of Hart et al (2011).…”

“…Saliva cortisol concentrations, at least in cows, were further shown to be independent of the animal's feeding actions, e.g. drinking, eating, and ruminating (Schwinn et al, 2016). At basal cortisol concentrations, we observed only weak correlations between SC, FC and TC, indicating that individual animals exhibit a considerable biological variation.…”

“…Estimating FC by measuring of SC represents a non-invasive approach, thereby assuming SC to reflect plasma FC that diffuses unhindered into saliva (Brossaud et al, 2015). Saliva cortisol is used in horses and dairy cows to estimate cortisol concentrations in blood (Scheidegger et al, 2016;Schwinn et al, 2016). Vining and McGinley (1987) confirmed that the equilibrium between concentrations of FC in plasma and cortisol in saliva establishes due to passive diffusion of plasma FC across the acinar cells of the salivary gland.…”

Holly polyphenols alleviate intestinal inflammation and alter microbiota composition in lipopolysaccharide-challenged pigs

“…HP supplementation increased the sucrase activity in both the jejunum and ileum of healthy piglets and jejunal lactase in LPS-challenged piglets, suggesting that dietary polyphenols could improve the intestinal digestive function of weanling piglets. The plasma cortisol concentration was increased in the piglets challenged with LPS, which is similar to the previous studies (23,24) . LPS leads to immune stress and affected nutrients digestion and metabolism.…”

Inflammatory and metabolic responses to an intramammary lipopolysaccharide challenge in early lactating cows supplemented with conjugated linoleic acid

“…The revised quantitative insulin sensitivity check index (RQUICKI) was calculated on a weekly basis according to Holtenius and Holtenius (2007) to estimate insulin sensitivity. For technical reasons, cortisol concentration in plasma was analysed only during the first 5.5 hr of the LPS challenge using a RIA based on an earlier description by Blum et al (1985) and Schwinn, Knight, Bruckmaier, and Gross (2016). Lactate dehydrogenase (LDH) activity in milk serum was determined using commercially available test kits (LDH IFCC, Axon Lab AG, Baden, Switzerland) with an automated analyser (Cobas Mira 2, Hoffmann-La Roche, Switzerland) according to the manufacturer's protocol.…”