Associations between ear necrosis in weaned pigs and biomarkers for inflammation, stress, and immune activation in oral fluid

Background Ear necrosis is prevalent in weaned pigs reared in intensive production systems and is associated with welfare, other health, and production concerns. However, there is a lack of knowledge about the physiological alterations in pigs with ear necrosis. This study used a panel of 11 analytes in oral fluids to explore associations between ear necrosis and markers for stress (cortisol, alpha-amylase, butrylcholinesterase (BChE)), inflammation (haptoglobin), immune activation (adenosine-deaminase, ferritin, interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor alpha, interferon-gamma), and general homeostasis (creatine kinase). Pigs ( n = 410) in 36 mixed-sex pens were scored for ear necrosis once per week for 6 weeks after weaning. Oral fluid samples were collected from pens once per week and from 61 individual pigs at week 5 post-weaning. Pens were categorised based on the proportion of pigs in the pen with ear necrosis at each week: Zero (0%), Low (> 0 and < 30%), High (≥ 30%). Individual pigs were categorised by ear necrosis score as none ( n = 30), mild ( n = 8), moderate ( n = 8), or severe ( n = 15). Associations between analyte levels and ear necrosis were assessed at both the pen and individual level, and the ability of early post-weaning analyte levels (weeks 1–3) to predict later pen-level prevalence (week 6) was also evaluated. Results At the pen level, High prevalence pens had increased levels of haptoglobin, IL-6, and IL-1β, and decreased levels of BChE, compared to Low or Zero prevalence pens (all P < 0.05). At the individual level, pigs with ear necrosis had higher haptoglobin levels than unaffected pigs, and pigs with moderate and severe scores had higher haptoglobin and IL-6 than pigs with no or mild ear necrosis (all P < 0.05). No differences were found for the remaining analytes ( P > 0.05). Elevated alpha-amylase at week 1 and BChE at week 2 (potentially reflecting a stress response) were associated with increased odds of later ear necrosis, while increasing BChE at week 3 (potentially reflecting lower inflammation) was associated with decreased odds. Conclusion Ear necrosis was associated with deviations in inflammatory and immune activation markers. Future research should investigate the physiological changes over a longer period and determine if this is associated with other, potentially long-term, health and welfare consequences of ear necrosis. Clinical trial number Not applicable.