Guttural pouch empyema caused by Corynebacterium pseudotuberculosis in a pregnant mare

During medical management of mild colic in a 12-year-old Quarter Horse, mid-gestation mare, unilateral purulent nasal discharge from the right nostril was noted. Endoscopic examination revealed guttural pouch empyema. Culture was positive for Corynebacterium pseudotuberculosis and negative for Streptococcus equi ssp. equi. A synergistic haemolysis inhibition titre of 1024 was consistent with C. pseudotuberculosis infection. Treatment included serial lavages and local infusion of antibiotics into the guttural pouches along with a 6-week course of oral trimethoprim-sulfamethoxazole and rifampicin. Overall, no additional sites of infection were identified and the mare responded well to treatment, delivering a healthy, full-term foal. This case emphasises that C. pseudotuberculosis, although uncommon, should be considered as a differential for guttural pouch empyema.