Dominance status assessed using a food competition test influences plasma
cortisol levels and cell mediated immunity in growing pigs
B.M. Hjarvard1, O.N. Larsen2, H.R.J. Madsen1 and
K.H. Jensen1
1Department of Animal Health, Welfare and Nutrition,
Danish Institute of Agricultural Sciences, Research Centre Foulum, Tjele,
Denmark
2Institute of Biology, University of Southern Denmark, DK-5230 Odense
M, Denmark
The pig is used in human medicine due to its physiological similarities
with humans. Hence,
the purpose of this study was to investigate whether rank, a psychosocial
factor, could
account for endocrine and immune differences among group members in a
stable social
environment and thus present a natural stress model.
Subjects were female growing pigs (n=36) housed in groups of four. Rank
was assessed using a food-competition-test with precedence to the feeder
as the determining variable. Endocrine and immune functions were evaluated
by measuring plasma cortisol and cell immune phenotypes. The percentage
of cells marked for TLR4, SLA II, CD4+ and CD8+ molecules was determined
by flow cytometry. Plasma cortisol was determined by radioimmunoassay.
Mean growth was higher in both high (HR) and middle ranking (MR) pigs
than in low ranking
(LR) pigs. Plasma levels of cortisol related to rank (p<0.05) and were
lower in MR pigs than
in HR and LR pigs. The percentage of SLAII expressing cells varied with
rank (p<0.05) and
was highest in HR pigs. The percentage of CD4+ and CD8+ lymphocytes decreased
over the
experimental period. The combined effect of these changes was a decrease
in CD4:CD8 ratio
that tended to relate to rank (p<0.1). The decrease was most pronounced
in low ranking (LR)
pigs. The percentage of TLR4 marked cells showed no relationship with
rank.
The rank-related inverse relationship between percentage of SLA II expression
and
difference in CD4:CD8 ratio suggests an interconnection between variables
affecting the
immune system. Thus, rank seems to affect immune and endocrine variables
differently. The
relationship between psychosocial factors and cellular immune system may
have important
implications for disease progression and for the management, treatment
and selection of
pig subjects for studies in which immunological variables are of interest.
Paper presented
at Measuring Behavior 2005
, 5th International Conference on Methods and Techniques
in Behavioral Research, 30 August - 2 September 2005, Wageningen, The
Netherlands.
© 2005 Noldus
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