Patho-epidemiological Study of Chronic Respiratory Disease (CRD) in Commercial Layer Chickens: A Case Report

Chronic Respiratory Disease (CRD), caused by Mycoplasma gallisepticum , is one of the most economically significant diseases of poultry worldwide. This case report describes the clinical, pathological, and epidemiological features of CRD in a commercial layer flock in Jigjiga, Somali Regional State, Ethiopia. A total of 5,100layer chickens reared under a deep litter system were affected. The outbreak resulted in 505 deaths, representing an overall mortality of 9.90%, and 1,417 clinically affected birds, giving a morbidity rate of 27.78%. Morbidity and mortality were higher in Block B (33.11% and 10.88%) than in Block A (25.11% and 9.41%), indicating increased susceptibility among older birds. Clinically, affected chickens exhibited respiratory distress, coughing, nasal discharge, and open-mouth breathing. Postmortem findings included catarrhal exudate in the trachea and bronchi, cloudy and foamy air sacs, and air sacculitis. Based on clinical signs and gross pathology, the condition was diagnosed as CRD. Treatment with Tylosin 20% (0.5 g/L of drinking water), coupled with improved ventilation, reduced overcrowding, and strict biosecurity, resulted in recovery of the flock. The study highlights the continued importance of CRD as a major health and economic threat in layer operations and underscores the need for routine monitoring, early diagnosis, and effective preventive measures.