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Online Journal of Veterinary Research

 Volume 22 (2): 139-149, 2018.

Effects of relative humidity and commercial medicinal treatments on complex respiratory infections and pathology in broilers.


Faghihzadeh S., DVM, Asasi K., DVM, PhD, Abdi-Hachesoo B., DVM, PhD.


Poultry Diseases Research Center, Department of Clinical Studies, School of Veterinary Medicine, Shiraz University, Shiraz, Iran.



Faghihzadeh S, Asasi K, PhD, Abdi-Hachesoo B., Effects of relative humidity and commercial medicinal treatments on complex respiratory infections and pathology in broilers. Onl J Vet Res., 22 (2): 139-149, 2018. Respiratory complex infections are the most common cause of mortality in broiler chicken farms in developing countries. We report effects of 25 to 80% relative humidity (RH) on treatments with Bromhexine and Bronchimax in broilers inoculated with infectious bronchitis virus (IRFIBV32), avian influenza virus (H9N2) and E. coli (O2). Nine groups of 43 broiler chicks were challenged and 3 groups of 20 were used as unchallenged controls but all received treatments and were exposed to 3 levels of RH. Results showed highest mortality rates (28%) occurred at low relative humidity in broilers given Bronchimax and lowest mortality (11.5%) in high relative humidity without treatments (P < 0.05). Oral mucosal discharges were significantly higher in groups exposed to high humidity with Bromhexine and/or high humidity with Bronchimax compared with other groups (P≤0.05). Syrinx casts, were lower in those exposed to 50-55% RH and treated with Bromhexine (P≤0.05). In dead birds, aggregation of fibrinous exudate occluded the syrinx leading to asphyxiation. We report clinical signs, necropsy findings, tracheal histopathology, ciliary stasis scores, serology and RT-PCR results for all poultry affected by complex respiratory disease. High relative humidity may decrease mortality but mucolytic and/or herbal treatments, increase mortality in chickens infected with respiratory complex agents.


Key Words: Respiratory Complex, Relative Humidity, Mucolytic drugs, IBV, H9N2, E. coli.