The effect of stocking density and enrichment on hair cortisol, hair dehydroepiandrosterone (sulphate) and their ratio in growing-finishing pigs

Understanding how husbandry practices affect chronic stress in growing-finishing pigs is essential to improve their welfare. The objective of this study was therefore to investigate the effect of two important practices, i.e., stocking density and enrichment, within different husbandry systems by studying concentrations of hair cortisol and hair dehydroepiandrosterone (sulphate) (DHEA(S)) and their ratio, as markers for chronic stress. Hereto, in six experiments, various organic and conventional systems were studied in which the stocking density and the level of enrichment varied. We found that a lower stocking density generally resulted in lower hair cortisol and DHEA(S) concentrations, but the effect of stocking density on the hair cortisol/DHEA(S) ratio was less clear. Access to enrichment only tended to result in higher DHEA(S) concentrations in one of the experiments. Furthermore, sex tended to affect or affected hair cortisol, DHEA(S) and/or the ratio only in some of the experiments. These results suggest that a lower stocking density is beneficial for growing-finishing pigs as they seemed to be less chronically stressed. That the enrichment items did not beneficially affect hair cortisol and DHEA(S) was likely due to the relatively small contrast between the control and enriched condition, as the pigs in the control condition already had access to straw. As not much studies have investigated hair DHEA(S) concentrations in pigs, more research is needed to get more insight of this hormone in relation to chronic stress and the effect of sex in pigs.