Endocrine response to acute stress in pigs with differing backtest scores

Abstract

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 reaction to stress than those scoring lower on the test. To further understand this reaction eighty-eight gilts from 19L 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 challenges. Pigs, in two replicates, were fitted with jugular cannulas at approximately 150d of age. An acclimation time of 24h 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 120m relative to the application of the stressor). Pigs were challenged with 0.11mol/kg BW of corticotropin releasing hormone (CRH) (n=9 High, n=9 Low) injected through the cannula to test the proposed model. The first stressor was snaring the pig with a nose-snare for 1min (n=10 High, n=9 Low). The second stressor was depriving the pigs of feed for 24h 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 including 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 10m and returned to basal levels by 90m. Least squares means response in norepinephrine of the High exceeded Low at 5m by 376±99pg/mL. Cortisol, epinephrine, and norepinephrine response to snaring was similar. Cortisol peaked at 10m and epinephrine and norepinephrine at 5m. The response to feed deprivation failed to exceed basal levels. Response to the CRH challenge demonstrated the appropriateness 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 5m following snaring is unknown.