Endocrine response to acute stress in pigs with differing backtest scores B.D. Velie 1 , J.P. Cassady 2 , C.S. Whisnant ⁎ North Carolina State University, Raleigh, NC 27695-7621, United States article info abstract Article history: Received 8 April 2011 Received in revised form 21 December 2011 Accepted 12 January 2012 In an attempt to quantify a pig's behavioral reaction to stress, pigs in previous studies were subjected to a backtest. Pigs scoring high on the backtest were thought to have a greater reac- tion to stress than those scoring lower on the test. To further understand this reaction eighty- eight gilts from 19 L were tested twice using the backtest. Gilts with the greatest (n = 15, High) and least (n = 15, Low) total time struggling were then selected for acute stress chal- lenges. Pigs, in two replicates, were fitted with jugular cannulas at approximately 150 d of age. An acclimation time of 24 h was given between cannulation, testing and between tests. Blood samples were collected at 10 time points (-60, -30, 0, 5, 10, 15, 30, 60, 90, and 120 m relative to the application of the stressor). Pigs were challenged with 0.11 mol/kg BW of corticotropin releasing hormone (CRH) (n = 9 High, n = 9 Low) injected through the cannu- la to test the proposed model. The first stressor was snaring the pig with a nose-snare for 1 min (n = 10 High, n = 9 Low). The second stressor was depriving the pigs of feed for 24 h followed by placing feed next to the pig but out of reach (n = 6 High, n = 7 Low). Plasma samples were assayed for cortisol, epinephrine, and norepinephrine. Data were analyzed using a model in- cluding fixed effects of time, replicate, and group (High or Low) and all two-way interactions. In response to the CRH challenge, cortisol levels peaked at 10 m and returned to basal levels by 90 m. Least squares means response in norepinephrine of the High exceeded Low at 5 m by 376 ± 99 pg/mL. Cortisol, epinephrine, and norepinephrine response to snaring was similar. Cortisol peaked at 10 m and epinephrine and norepinephrine at 5 m. The response to feed dep- rivation failed to exceed basal levels. Response to the CRH challenge demonstrated the appro- priateness of the model and that High and Low pigs were equally capable of responding. The biological significance of differences between High and Low groups in norepinephrine levels at 5 m following snaring is unknown. © 2012 Elsevier B.V. All rights reserved. Keywords: Pigs Behavior Stress Cortisol Epinephrine Norepinephrine 1. Introduction The backtest is a heritable behavioral trait measured early in life and has been previously associated with performance traits in pigs (Velie et al., 2009). Previous studies used the backtest as a measure of a pig's ability to cope with stressful situations; however, conflicting evidence has been shown re- garding this theory (Hessing et al., 1993; 1994). Geverink et al. (2002) reported higher basal cortisol in low resisting pigs. Hessing et al. (1994) also found higher basal cortisol but cortisol concentrations and heart rates were lower after an open field test in low resisters. Cassady (2007) found no correlation between backtest score and scores on a resident intruder test. However backtest score was correlated with av- erage daily gain. van Erp-van der Kooij et al. (2003) demon- strated that weaning and mixing caused significant rises in cortisol in animals scoring high and low on the backtest while moving and weighing did not. If the backtest is truly Livestock Science 145 (2012) 140–144 ⁎ Corresponding author at: Department of Animal Science, PO Box 7621, Raleigh, NC 27695, United States. Tel.: +1 919 513 1115; fax: +1 919 515 6884. E-mail addresses: scott_whisnant@ncsu.edu (C.S. Whisnant), Joe_Cassady@ncsu.edu (J.P. Cassady). 1 Current address: Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2006, Australia. 2 Senior author: Department of Animal Science, 232B Polk Hall, Raleigh, NC 27695, United States. Tel.: +1 919 359 0503; fax: +1 919 515 7780. 1871-1413/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2012.01.008 Contents lists available at SciVerse ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci