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Abstract
Previously we showed that pigs reared in an enriched environment had higher baseline
salivary cortisol concentrations during the light period than pigs reared under barren
conditions. In the present experiment, it was investigated whether these higher baseline
salivary cortisol concentrations were a real difference in cortisol concentration
or merely represented a phase difference in circadian rhythm. The effects of different
cortisol concentrations on the behavioral responses to novelty and learning and long-term
memory in a maze test were also studied in enriched and barren housed pigs. At 9 weeks
of age enriched and barren housed pigs did not differ in baseline salivary cortisol
concentrations nor in circadian rhythm, but at 22 weeks of age barren housed pigs
had a blunted circadian rhythm in salivary cortisol as compared to enriched housed
pigs. The differences in baseline salivary cortisol concentrations between enriched-
and barren-housed pigs are age-dependent, and become visible after 15 weeks of age.
Enriched- and barren-housed piglets did not differ in time spent on exploration in
the novel environment test. Barren-housed pigs had an impaired long-term memory in
the maze test compared to enriched-housed pigs; however, no differences in learning
abilities between enriched- and barren-housed pigs were found. Because blunted circadian
cortisol rhythms are often recorded during states of chronic stress in pigs and rats
or during depression in humans, it is suggested that the blunted circadian rhythm
in cortisol in barren-housed pigs similarily may reflect decreased welfare.