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 wee ks 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 includin g an area which contained peat and straw in a rack. Behavioural observation s showed that environmental enrichment reduced time spent inactive and rime spent involved in harmful social and aggressive behaviour (P < 0.001). Eac h 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 g lands were weighed and hearts were examined for endothelial haemorrhages. P igs from enriched environments appeared less fearful during the novel pen t est by showing a shorter latency to contact the novel object (P < 0.001) an d spending move time in contact with it (P < 0.05). Plasma cortisol respons es to the novel pen test tended to be higher in pigs from enriched environm ents (P < 0.05) and pigs from enriched environments had significantly highe r 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 a ctivation of the pituitary-adrenal axis in barren environments led to a sup pression of cortisol responses to acute stress. The higher cortisol respons es to the novel pen test in pigs from enriched environments may also have r esulted from greater levels of behavioural activity. This could also explai n 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 end othelium of the heart (P < 0.05) may mean they had a more reactive sympathe tic nervous system.