Influence of environmental enrichment on welfare-related behavioural and physiological parameters in growing pigs

Three hundred and twenty pigs were reared from birth to slaughter at 21 weeks in either barren or enriched environments. The barren environments were defined as intensive housing (slatted floors and minimum recommended space allowances) and the enriched environments incorporated extra space including an area which contained peat and straw in a rack. Behavioural observations showed that environmental enrichment reduced time spent inactive and rime spent involved in harmful social and aggressive behaviour (P < 0.001). Each pig was individually exposed to a novel object during a novel pen test at 18 weeks of age and behavioural, heart rate and plasma cortisol responses were recorded. At slaughter plasma cortisol levels were measured, adrenal glands were weighed and hearts were examined for endothelial haemorrhages. Pigs from enriched environments appeared less fearful during the novel pen test by showing a shorter latency to contact the novel object (P < 0.001) and spending move time in contact with it (P < 0.05). Plasma cortisol responses to the novel pen test tended to be higher in pigs from enriched environments (P < 0.05) and pigs from enriched environments had significantly higher cortisol levels at slaughter (P < 0.05). Adrenal weights were greater in pigs from barren environments (P < 0.05) and it is suggested that chronic activation of the pituitary-adrenal axis in barren environments led to a suppression of cortisol responses to acute stress. The higher cortisol responses to the novel pen test in pigs from enriched environments may also have resulted from greater levels of behavioural activity. This could also explain the higher maximum heart rates in pigs from enriched environments during the ist min of the test (P < 0.05) and during the period prior to the test when they were being driven towards the test arena (P < 0.05). However, the fact that enriched pigs also showed a greater number of lesions to the endothelium of the heart (P < 0.05) may mean they had a more reactive sympathetic nervous system.