Animal (Jan 2010)
Environmental enrichment in early life affects cortisol patterns in growing pigs
Abstract
Effects of environmental enrichment at different stages of life on stress physiology of pigs were investigated in a trial with 63 groups, each of four siblings. In each of the three growing phases (suckling 0 to 4 weeks of age, nursery 5 to 9 weeks, fattening 10 to 24 weeks) pens either were (=E) or were not (=0) enriched. Accordingly, the treatments were (i) 000, (ii) E00, (iii) EE0, (iv) 00E, (v) 0EE and (vi) EEE. The enrichment material, renewed twice daily to leave a thin layer, consisted of wood shavings and chopped straw. Salivary cortisol was sampled hourly from 0700 to 1900 h at the age of 9 and 21 weeks. The presence of a circadian secretion rhythm was evaluated by an intra-assay coefficient of variation-based method. An adrenocorticotropic hormone test was performed at 21 weeks. Treatment effects on the odds of a physiological cortisol rhythm were assessed by logistic regression, and effects on cortisol concentrations with a repeated measures GLM. Substrate-enrichment from 0 to 9 weeks of age increased the odds of a rhythm as compared to barren housing (odds ratio (OR) = 30.0, P < 0.01). A flat cortisol secretion pattern may indicate chronic stress and/or delayed maturation of the rhythm. Barren as compared to enriched rearing (0 to 4 weeks of age) seemed to cause a blunted secretion rhythm at 21 weeks of age. Although behavioural and tail lesion observations provided support to the assumption that a blunted rhythm indicates chronic stress, the biological significance of these cortisol results needs confirmation in future studies.
