Adrenal glands as a potential animal welfare indicator in pigs

The aim of this study was to test the adrenal gland mass (NNM) as a post-mortem indicator of chronic stress in pigs. This was addressed by the question whether husbandry systems that better meet the animals' needs for outdoor stimuli and rooting areas, or health status, lead to reduced NNM (less stress/negative emotions). 229 adrenal glands of pigs from three farms were collected at slaughter and possible influences of the husbandry systems and fattening batches on the NNM were estimated by a linear mixed model. Furthermore, the linear relationship between NNM and health indicators were investigated at the batch level by a correlation analysis. On the individual animal level, the influence of health status was analysed. The results show significant influences of farm (semipartial r2 = 0.14; 95%-CI = 0,06-0,22) and batch (semipartial r2 = 0.12; 95%-CI = 0.04-0.19). Pigs of the summer-batch of the organic farm had lower estimated NNM values with 2.15 (+/- 0.04) g than the animals of the other batches. In summer, the increased use of the outdoor arena seems to generate more space as well as occupation, which possibly reduced stress. Similarly, the NNM was positively correlated with the health indicators "tail posture" (r = 0.72) and "wounds" (r = 0.75). Husbandry system (farm) and stressful events during a batch thus influence the NNM. In addition, there is a correlation with the health indicators recorded in this study, but this was not confirmed at the individual animal level. The suitability of the NNM as an animal welfare indicator remains questionable, also for reasons of feasibility.