The relationship between housing and social rank on cortisol, β-endorphin and dynorphin (1–13) secretion in sows

Abstract

Endogenous opioids and glucocorticoids may be useful welfare indicators in pigs. Measures of plasma cortisol were carried out in plasma samples collected hourly, from 8:00 to 17:00 h from High Ranking (HR) ( n=5) Middle Ranking (MR) ( n=7) and Low Ranking (LR) ( n=4) group housed sows and from eight Stall Housed Sows (SHS). Cerebrospinal fluid (CSF) was collected after pentobarbital injection ( n=17; HR n=2; MR n=3; LR n=4 and SHS n=8) and the levels of β-endorphin and dynorphin monitored. Brains were removed, weighed and frozen. Cortisol, β-endorphin and dynorphin were measured in extracts of frontal cortex. LR sows had significantly lighter brains than HR sows (LR=126.05±2.18 and HR=144.86±3.97) and showed no circadian pattern in cortisol secretion. HR and LR sows had lower cortisol levels than MR sows. There was an indication that HR, MR and stall housed sows tended to have lower β-endorphin levels in the CSF than LR sows (0.83 pg/ml±0.39; 1.66 pg/ml±0.472; 1.07 pg/ml±0.267 and 6.81 pg/ml±3.27 respectively). Mean dynorphin (1–13) levels in the CSF were 12.56 pg/ml (±5.49). Sows kept in stalls had higher levels of dynorphin in the frontal cortex than group housed sows.