Prolonged head elevation causes mucosal IgA fluctuation in horses

Abstract Text:

Stress has a pronounced effect on immune cells and their ability to mount an effective defense against pathogens. Prolonged head elevation is thought to be a major contributor to the increased risk of respiratory disease associated with transportation in horses. Elevated cortisol and changes in leukocyte populations in response to transportation stress are well documented in horses. Few studies have investigated other aspects of immune function that may predispose horses to respiratory disease following head elevation. The objective of this study was to determine if prolonged head elevation affects mucosal IgA secretions and to evaluate the potential use of mucosal IgA as indicators of stress. Twelve horses (mean ± SEM, 552 ± 10 kg; 11.5 ± 1.4 y) were tethered for 12 h with their heads elevated at a height of 1.5 m to induce physiological stress. While tied, horses had unlimited access to bermudagrass hay and were offered water every 2 h. Each horse underwent head elevation on 4 occasions, each separated by 30 d. When not tied, horses were maintained on pasture forage. Nasopharyngeal flush (NPF), whole blood, saliva and fecal samples were obtained before head elevation (Pre), immediately after (0 h), and 12, 24, and 72 h post head elevation. Cortisol concentration was measured in serum and saliva and IgA concentration was measured in NPF, saliva, and fecal water. Data were compared using mixed model ANOVA with repeated measures. Both serum and saliva cortisol were elevated after head elevation (P<0.0001) and returned to baseline by 12 h post. Salivary (P=0.0005) and fecal water (P=0.01) IgA were elevated above Pre at 0 h post. At 12 h post, salivary (P<0.0001) and NPF (P<0.0001) IgA were lower than Pre. Fecal water IgA remained elevated above Pre at 12 h post (P=0.04), but dropped below Pre at 24 h post (P=0.005). Salivary IgA remained lower through 72 h post (P=0.006), whereas NPF and fecal water IgA returned to normal by 24 and 72 h post, respectively. Prolonged head elevation induced physiological stress and alterations in protective mucosal secretions. Instability in IgA secretions may partially explain the heightened risk for respiratory disease following transportation. Persistent fluctuations in mucosal IgA suggests the time course of physiological stress may exceed that represented by the transient elevation of cortisol. Mucosal IgA secretions may be good indicators of both acute and chronic stress in horses.

 Keywords: Stress, Immunosuppression, Respiratory