Determining the adrenocortical activity as a measure of stress in domestic pigs (Sus scrofa domesticus) based on salivary and faecal analysis

Abstract

Domestic pigs are subjected to farm management procedures, some of which might be perceived as causing stress and therefore may have welfare concerns. When confronted with a stressor, animals display a response that consists of a suite of physiological and behavioural alterations to restore homeostasis. Physiologically, the response is usually determined using glucocorticoid concentrations (GC) albeit invasively, with the disadvantage of a possible handling-induced stress response. To date, no non-invasive method exists for determining stress-related responses in pigs. This study aimed to examine the suitability of enzyme-immunoassays (EIAs) for determining GC concentrations in saliva and faeces of domestic pigs by performing an ACTH challenge. A total of 6 animals were studied with 4 receiving 10µg/kg of Synacthen® (Novartis, South Africa Pty Ltd) and the remaining 2 receiving 0.5 ml physiologic saline. Baseline salivary glucocorticoid (sGC) concentrations of 2.38±1.83ng/ml (mean±SEM) increased by six-fold (14.03±6.83 ng/ml) within 40-90 minutes after administration of ACTH (P < 0.0001) and the elevated salivary cortisol levels were maintained for up to nine hours. Administration of saline caused no significant differences in sGC concentrations (P = 0.82). Similarly, baseline faecal glucocorticoid metabolite (fGCM) level of 235±46μg/g rose significantly up to 393±164μg/g within 36 hours post ACTH administration (P < 0.0001). No significant difference was found between baseline and post saline administration (P = 0.57). Significantly higher sGC concentrations were found in samples collected in the morning compared to those collected in the afternoon, indicating a circadian rhythm. In terms of stability of fGCMs, post-defecation levels only changed by 4% over the course of 50h (P = 0.76). In conclusion, EIAs can be used to determine sGC and fGCM concentrations to assess adrenocortical function in pigs. FGCM levels are relatively stable for at least two days post-defecation, which facilitates field sample submissions.