21 Mucosal IgA displays an unclear pattern throughout the day in horses

Mucosal immunoglobulin (Ig) A is a useful indicator of immunity, a sensitive biomarker for stress and a desirable target for more effective vaccine development. In human medicine, treating diseases at specific times of the day, known as chronotherapy, is rapidly becoming an accepted practice. Equine research suggests protection obtained from vaccines may be enhanced with timed delivery. Reports of diurnality of both fecal and salivary IgA exist in other species, but this has not been confirmed in horses. The aim of this preliminary study was to investigate IgA for 24-h rhythmicity. Four mature Quarter horse geldings (mean ± SEM, 600 ± 27 kg; 10.3 ± 4.0 y) were housed according to their normal daily routine under natural summer conditions; outside in individual dry lots for 12 h and stalled inside overnight. Sunrise and sunset were at 0600 and 2000 h, respectively. Horses were fed the same quantities of concentrate and bermudagrass hay twice daily. Venous blood, fecal and saliva samples were collected at 6-h intervals (0600, 1200, 1800, 2400 h) for 4 consecutive days using only headlamps to collect samples after sunset. Cortisol and IgA concentrations were determined by ELISA. Data were log-transformed, blocked by day, and compared using mixed model ANOVA with time as a repeated variable. Serum cortisol displayed an expected cyclical pattern with the greatest concentrations observed at 0600 h (P