Impacts of chronic stress and social status on various physiological and performance measures in pigs of different breeds1

Abstract

Pigs typically experience various environmental stressors, which can negatively affect performance. Cortisol concentrations and various immune and performance measures are influenced by breed, but few data exist describing the impact of breed on stress responsiveness in pigs. The objective of this experiment was to determine if certain physiological responses to chronic stressors differed among 3 breeds and 2 commercial lines of pigs. The pigs were Landrace (n = 36), Meishan (n = 30), Yorkshire (n = 32), or 1 of 2 commercial lines (Line-A and Line-B; both n = 36). All pigs were weaned at 17 to 21 d and kept in a common nursery. At 49 d of age, pigs were assigned to 1 of 2 treatments: stress (heat, crowding, and mixing) or control (no stress treatment). Pigs were allocated to groups of 3 pigs per pen of the same sex. Control pigs were kept with their littermates. At the onset of the experiment, stressed pigs were mixed with 2 unfamiliar pigs once, and heat and crowding stressors were implemented simultaneously for 14 d. Pigs allocated to the stress treatment were video-recorded for 24 h following initiation of mixing to determine social status: dominant, intermediate, or submissive. Blood samples were taken at d 0 (baseline), 1, 7, and 14 to assess cortisol concentrations and immune measures. Breed and treatment affected cortisol, immune, and performance measures, but no significant breed x treatment interactions were found. In general, pigs subjected to the chronic stressor had lower (P < 0.001) BW and ADG (P < 0.001) than did control pigs. Plasma cortisol was lower (P < 0.001) among stressed pigs at d 7 and 14. Regardless of breed, lipopolysaccharide-induced proliferation (P < 0.01) and natural killer (NK; P < 0.005) cytotoxicity were greater in stressed pigs compared with controls. Furthermore, among stressed pigs, dominant pigs had a greater total white blood cell count (P < 0.005), NK (P < 0.05), and phagocytosis (P < 0.05) than the subordinate pigs. The results indicate that pig breed did not influence the physiological responses to the chronic concurrent stressors imposed for 14 d in this study, but social status did influence the immune responsiveness of these pigs to heat, crowding, and mixing.

The impact of chronic environmental stressors on growing pigs, Sus scrofa (Part 1): stress physiology, production and play behaviour

“…This is corroborated by the finding that the larger the pigs' adrenal cortices were, the lower their salivary cortisol levels tended to be. Sutherland et al (2006) found that 7-week-old pigs exposed to multiple concurrent stressors (mixing, crowding and heat stress of 33 6 58C) for 14 days had significantly lower plasma cortisol concentrations when measured at both 7 and 14 days after the onset of these conditions. Lower salivary cortisol levels are often observed under conditions of chronic stress and can be attributed to the dynamics of the HPA response; cortisol levels are elevated shortly after the axis is activated, but eventually a counter-regulatory response can lead to circulating cortisol concentrations below that of pre-stress levels (Miller et al, 2007).…”

“…Production parameters of weight gain, food conversion efficiency and back fat were recorded as a strong link between chronic stress and poor growth performance is frequently observed (e.g. Hyun et al, 1998;Sutherland et al, 2006;Foury et al, 2007). One of the key causal mechanisms of this relationship is thought to be the general catabolic influence of high circulating cortisol on certain muscle types and fat cells (Sapolsky et al, 2000;Yoshioka et al, 2005).…”

Heat stress upregulation of Toll-like receptors 2/4 and acute inflammatory cytokines in peripheral blood mononuclear cell (PBMC) of Bama miniature pigs: an in vivo and in vitro study

“…Although many stressors have been reported to increase plasma cortisol concentrations in pigs (Becker et al, 1985;Parrott and Misson, 1989), conflicting results have been reported by other researchers. For example, lower cortisol levels were detected in heat-stressed pigs compared with coldstressed and transportation-stressed pigs, with statistically similar values for cortisol compared with control pigs (Hicks et al, 1998, Sutherland et al, 2006. Furthermore, heat stress did not increase plasma cortisol in cows with the exception of a slight elevation on the first day of heat stress (Farooq et al, 2010).…”

Parenteral administration of vitamins A, D and E on the oxidative metabolism and function of polymorphonuclear leukocytes in swine

“…Maternal separation, relocation, introduction to new social groups, the establishment of social dominance and a change in diet to a higher dry mass content induce physiological changes in recently weaned swine, with a consequent reduction in weight gain being observed (Sutherland et al 2006, Kojima et al 2008. These alterations lead to increased cortisol serum levels (Heo et al 2003) and possible effects on the immune response of animals (Bonnette et al 1990), such as a reduction in neutrophil microbicidal capacity and reduced function of natural killer cells and lymphocytes (Sutherland et al 2006, Da Costa et al 2008.…”

“…These alterations lead to increased cortisol serum levels (Heo et al 2003) and possible effects on the immune response of animals (Bonnette et al 1990), such as a reduction in neutrophil microbicidal capacity and reduced function of natural killer cells and lymphocytes (Sutherland et al 2006, Da Costa et al 2008. Metz and Gonyou (1990) observed that the immune system of swine weaned at four weeks of age is not yet fully developed.…”