Leukocyte coping capacity to measure infection/vaccination related stress in weaning piglets

The assessment of stress and pain in animals presents a persistent challenge in veterinary medicine, often lacking a universally accepted golden standard. The Leukocyte Coping Capacity (LCC) is an innovative functional assay measuring the ability of polymorphonuclear neutrophils (PMNLs) to produce reactive oxygen species (ROS) upon stimulation. Low LCC values have been associated with increased stress, while high values suggest a reduced stress burden. This study investigated the utility of LCC as an indicator of immune response to infection and vaccination related stress in weaned piglets. Fifty-two commercial weaned piglets were randomly assigned to four experimental groups (G1, G2, G3 Control G4). G1 and G2 were infected intranasally with two distinct Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV1) isolates, G3 was vaccinated intramuscularly with a modified live virus vaccine, and G4 served as the control group. Blood samples were collected eight times over 28 days to measure LCC Area Under the Curve (AUC) and the Myeloperoxidase Index (MPXI). A linear mixed-effects model was used for statistical analysis. The LCC assay successfully produced a clear, measurable effect. While infected groups (G1, G2) and the control group (CG4) showed relatively stable LCC AUC values throughout the trial, the vaccinated group (G3) exhibited a rapid and substantial increase in LCC AUC, peaking around day 14 at mean values exceeding 7,000–8,000, followed by a sharp decline. This elevation suggests a transient hyperactivation of neutrophil function in response to vaccine. Conversely, no significant differences were observed in MPXI values between groups. Total leukocyte and neutrophil counts across all groups showed a progressive, age-related decline over the 28-day period. This study demonstrates that the LCC assay is a valuable functional tool for assessing neutrophil oxidative activity in weaned piglets, particularly highlighting a potent, measurable immune response following vaccination. This approach can provide standardized and objective insights into the immune status of swine and supports LCC as a promising technique for evaluating the physiological impact of interventions, such as vaccination and infection, in a field setting.