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

Abstract

A pig is any listed animal species in the genus Sus, within the family Suidae of even-toed ungulates. The domestic pig (Sus scrofa domesticus) (also referred to as swine or hog) is a large, domesticated, eventoed ungulate that has its ancestry in the wild boar. Domesticated pigs are commonly raised as livestock by farmers for pork, hams, gammon or bacon), as well as for leather. For the Pig industry, chronic stress posed by gestation crates and its often negative consequences are a welfare concern, since stressors can negatively affect animal production as well as the health of pigs. When confronted with a stressor, an individual displays a stress response consisting of a suite of physiological and behavioral alterations to cope with the challenge. In pigs, the assessment of physiological responses to stress, like the related alterations in glucocorticoid (GC) concentrations, has already been done, but only by using an invasive approach, with the disadvantage of a possible handlinginduced stress response. So far, no validated non-invasive method for determining stress-related responses in pigs seems available. Therefore the study aimed to determine validated stress-related physiological responses in domestic pigs’ saliva and faeces through the performance of an adrenocorticotropic hormone stimulation test (ACTH challenge test), the effect of circadian rhythm on faecal GC levels and to investigate the effect of storage on the rate of metabolism of faecal glucocorticoid metabolites post-defaecation. An ACTH challenge was performed on four pigs and with two pigs as saline controls, at University of Pretoria Biomedical Research Centre (UPBRC), South Africa. Faecal GC metabolites (fGCM) were validated against four enzyme immuno-assays including the 3α,11-oxo-CM, 3β,11β-diol-CM, 11,17-DOA and cortisol. The 3β,11β-diol-CM method was subsequently selected and used to investigate for salivary and faecal GCM. The results indicated that acute salivary cortisol levels can increase up to ~600 % above the pre-injection baseline levels within 40 to 60 minutes post-injection. Faecal glucocorticoid metabolites (FGCM) levels in the 4 ACTH inoculated pigs reached 2-fold peaks of pre-injection levels within 7 to 36 hours following treatment. Comparatively, the early morning saliva and faecal samples have higher glucocorticoid concentrations compared with the late afternoon samples. In addition, fGCM in faecal samples were relatively stable for over 48 hours demonstrating that faecal sample storage may not affect outcomes of non-invasive hormone monitoring to assess adrenocortical function in pigs. This method provides an empirically sound basis for a non-invasive monitoring of adrenocortical function in pigs and serves as template for further studies which may have value for the monitoring of adrenocortical function in populations of pigs in different housing units and other stressful conditions.