Serum cortisol concentrations in newborn foals are increased by transfusion with anti-rhodococcal hyperimmune plasma and inversely associated with immunoglobulin activity.

Abstract

BACKGROUND: Transfusion of Rhodococcus equi hyperimmune plasma (REHIP) to neonatal foals is done to reduce the incidence of rhodococcal pneumonia. OBJECTIVES: To determine effects in newborn foals of REHIP transfusion on serum cortisol concentrations; the association of serum cortisol concentrations with serum globulin concentration and anti-rhodococcal immunoglobulin activity; and cumulative incidence of rhodococcal pneumonia. METHODS: Serum samples were collected from 356 newborn foals from 13 New York farms immediately before and after transfusion of 1 L or 2 L of REHIP. Serum samples were assayed for concentrations of cortisol, total globulins and immunoglobulin activities against virulence associated protein A (VapA). Data were analyzed using linear mixed-effects regression, chi-squared testing, and Spearman rank correlation coefficient. RESULTS: REHIP transfusion increased (P < 0.05) cortisol concentration from a mean of 21.9 ng/mL to 44.1 ng/mL. Post-transfusion serum cortisol concentration was less (P < 0.05) for foals transfused with 1 L REHIP than with 2 L REHIP. Pre-transfusion serum cortisol was negatively associated (P < 0.05) with total globulins (r = -0.19) and anti-rhodococcal activities of immunoglobulin G(IgGr = -0.22) and immunoglobulin G(IgG; r = -0.16). Pre- and post-transfusion cortisol concentrations were not associated with pneumonia development. CONCLUSIONS: Cortisol concentrations are significantly increased by REHIP transfusion, and serum cortisol concentrations are inversely associated with serum immunoglobulin concentrations in foals. However, serum cortisol concentration was not associated with increased risk of rhodococcal pneumonia in this population of foals.