The effectiveness of vasopressin as an ACTH secretagogue in cattle differs with temperament Kevin O. Curley Jr. a,b,c , Don A. Neuendorff c , Andrew W. Lewis c , F.M. Rouquette Jr. c , Ronald D. Randel c , Thomas H. Welsh Jr. a,b, ⁎ a Department of Animal Science, Texas A&M University, College Station, TX 77843-2471, United States b Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77843-4458, United States c Texas AgriLife Research, The Texas A&M University System, Overton, TX 75684-0200, United States abstract article info Article history: Received 22 December 2009 Received in revised form 9 August 2010 Accepted 13 August 2010 Keywords: Bovine Temperament Pituitary–adrenal axis Vasopressin challenge Exit velocity By using the temperament selection criterion of exit velocity (EV), cattle typically exhibiting hypercorti- solism and a blunted response to exogenous corticotrophin-releasing hormone (CRH) can be identified via individual behavioral responses to handling. To further characterize hypothalamic–pituitary–adrenal (HPA) axis dysfunction associated with bovine temperament, the present study compared pituitary and adrenal activity, following stimulation with exogenous vasopressin (VP), in steers with an excitable or calm temperament. Serial blood samples were collected via indwelling jugular cannula for 6 h preceding and 6 h following administration of a VP bolus. Plasma concentrations of adrenocorticotropic hormone (ACTH) and cortisol were quantified by RIA to determine pituitary and adrenal responsiveness within temperament groups. Cortisol concentrations in excitable steers during the pre-challenge period revealed an increased initial adrenal reactivity to interactions with humans. Subsequent acclimation to the experimental surroundings yielded greater baseline cortisol concentrations in the cattle with an excitable temperament. Pituitary stimulation with VP resulted in a greater ACTH output from the excitable compared to the calm animals. The data presented herein provide additional evidence that HPA axis function in cattle of an excitable temperament may be akin to a state of chronic stress. The bovine temperament model may be of further use to both decipher mechanisms associated with HPA dysfunction and to elucidate physiological phenotypes or pathologies that have parallels in other species. © 2010 Elsevier Inc. All rights reserved. 1. Introduction The term temperament has been used to characterize behavioral responses of cattle to human–animal interactions [1]. If we assume that a fear response underpins animal reactions toward man, then a case could be made for those animals of poor temperament (i.e., individuals with a greater adverse reaction to human-handling) exhibiting a greater fear response in general. In addition to interactions with humans, fear responses of domestic animals may also arise from all or one of the following: social interactions; encounters with novel species and situations; or sudden stimuli that can be visual, auditory, or tactile in nature. Thus, temperament assessments may not only characterize an animal's response to human handling, but also reflect the relative ease of evoking an individual's fear response. Fear is a well known stimulus of the hypothalamic–pituitary– adrenal (HPA) axis and has been widely studied since the adrenal glands were associated with the fear response in Cannon's [2] depiction of the “fight or flight” reaction to stressors. As glucocorti- coids are the primary mediators of the HPA response, serum or plasma concentrations of these steroids can be utilized as physiologic indicators of an ongoing stress response or biological quantifications of an individual's stress responsiveness. In cattle, glucocorticoids have been associated with anxiety-related behaviors [3] and novel-object avoidance [4]. Concerning temperament in the bovine model, elevated cortisol concentrations have been observed in cattle that exhibit an excitable temperament when compared to calmer animals [5,6]. Additionally, data generated from exogenous stimulation of the HPA axis in cattle suggest a possible disparity in pituitary–adrenal response dynamics that is linked to temperament [7]. Vasopressin's (VP) role as an ACTH secretagogue was suggested in the early 1950 s [8]. Since then VP has been demonstrated to be an important component of the endocrine stress response (for review, see [9]). Synthetic VP has been shown to induce increased circulating cortisol concentrations in cattle [10] and has been demonstrated to do so via increasing ACTH release from the pituitary gland [11]. The Physiology & Behavior 101 (2010) 699–704 ⁎ Corresponding author. Department of Animal Science, Texas A&M University, College Station, TX 77843-2471, United States. Tel.: + 1 979 845 5929; fax: + 1 979 862 2662. E-mail address: twelsh@cvm.tamu.edu (T.H. Welsh). 0031-9384/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2010.08.009 Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb