Leucocyte coping capacity, serum cortisol and neutrophil to lymphocyte ratio in ponies exposed to repetitive handling during a research project

Introduction: Stress is an umbrella term indicating increasing allostatic load with the potential to reach a pathological state. In this context, cortisol levels and the neutrophil granulocytes to lymphocyte (N:L) ratio are expected to increase. On the functional pathway stress reduces the oxidative burst capacity of neutrophil granulocytes and therefore the leucocyte coping capacity (LCC) is impaired with increasing stress load. We hypothesized that in ponies subjected to repetitive handing LCC would decrease over time and to be negatively correlated with cortisol and N:L. Methods: LCC, measured by a portable chemiluminometer and assessed as LCC:N and areas under the curve (AUCLCC, AUCLCC:N), cortisol measured by a validated enzyme immunoassay and N:L were determined in nine ponies (mean age 6.5 years± 5.3 SD) involved in a study including at two-dose vaccination course 28 days (d) apart and an observation period of 42 d including repetitive handling and blood sampling. Stress indices were measured the day of vaccination or booster (d1, d28), 3 days later (d3, d31) and on d42 and compared to values before the start of the study (d-5) using mixed effect models. Further, Pearson’s correlations were explored between AUCLCC, AUCLCC:N, cortisol and N:L. Results: No clinically relevant side effects of vaccination were visible and the N:L was stable over time. The AUCLCC (p= 0.006), AUCLCC:N (p =0.009) and cortisol (p=0.007) decreased significantly over the observation period. No correlation was found between AUCLCC:N, cortisol or N:L. Conclusions: The decrease of AUCLCC, and AUCLCC:N indicates an increasing stress load over the observation period. However, this was not supported by cortisol, the N:L ratio or by their correlations. Clinical relevance: The absence of correlation between classical stress indices may reflect different endpoints within the stress response. LCC might be a more cumulative marker for stress and its related biological costs in horses.

Ruhr-Universität-Bochum
Stiftung Tierärztliche Hochschule Hannover