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Livestock Production
Tuesday, June 20, 2006 7:56:29 PM
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Environmental factors influence the prevalence of infectious bronchitis virus

J.C. Lopez and R. McFarlane


The aim of this study was determine the prevalence of infectious bronchitis virus (IBV) in broilers in late winter and search for associations with management or environmental factors

Analyses were conducted to assess associations between the presence of IBV in broilers and various risk factors such as ambient ammonia, oxygen, carbon dioxide, humidity and litter humidity.

In 2 of the 5 positive farms where IBV was detected there were accompanying clinical signs that suggested infectious bronchitis (IB).


More commonly uncomplicated infections with IBV were asymptomatic under good management. Ambient humidity was the only risk factor that showed an association (inverse) with the prevalence of IBV.

Infectious bronchitis (IB) is a highly contagious respiratory viral disease of chickens characterized by respiratory and renal pathology, a drop in egg production and egg quality in layers and decreased growth and feed efficiency in broiler chickens.

Seasonal cycles of infectious diseases have been attributed to environmental changes, pathogen appearance and disappearance and host-behavior changes.

Many diseases caused by coronavirus such as severe acute respiratory syndrome (SARS) and infectious bronchitis (IB), exhibit winter seasonality with the presence of persistent virus carriers. The prevalence of respiratory diseases peaks during winter in poultry farms and could be caused by ineffective ventilation because of the desire to conserve heat.

Reduced ventilation usually results in an increase in air pollutants, such as ammonia, carbon dioxide, dust and air-borne microorganisms.

Certain factors are known to reduce bird performance, but only a few of these factors have been studied in relation to an IBV infection.

Ten farms (the average size was 77,000 birds) were selected. Birds from these farms in the past have contained high levels of antibodies against IBV or exhibited productive problems. Birds within one of the sheds had some production or health signs that suggested the presence of IBV, or were known to have experienced clinical infectious bronchitis (IB) in the past.

This shed was defined as the case shed and the control shed was defined as the shed believed not to contain birds that had been affected by IB.

The flock in each shed had a high degree of similarity with respect to the age of birds, number of drinkers, nature of food and litter.

Based on the results of previous studies it was anticipated that higher levels of ammonia could increase the presence of IBV or exacerbate the clinical signs found in infected birds. Anderson et al. reported that 72 hours of exposure to ammonia concentrations in the range of 20 to 50 ppm significantly increased the infection rate of chickens with Newcastle disease virus when given as aerosol.

However, no association was found in this study.

Four of the six sheds positive for IBV had low ammonia levels (under 20 ppm).

Levels of oxygen and carbon dioxide in the poultry industry are used principally as criteria for an efficient ventilation system. Although 55% of the sheds in our studies had a low level of oxygen (under 20.5 %) and 40% had high levels of carbon dioxide (over 0.3 %), we did not find a significant association between the levels of oxygen or carbon dioxide and the detection of IBV.

In this trial, there was no significant relationship between the litter humidity and IBV occurrence. Indeed in the majority of the of the sheds positive for IBV, levels of litter humidity were higher than recommended (North and Bell, 1990).

We can conclude within the constraints of the similar management systems described, that humidity has an influence on the presence of IBV, but there was no influence due to temperature, ammonia, carbon dioxide, oxygen and litter humidity.



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Article made possible through the contribution of the Australian Poultry Science Symposium (APSS) 2006.

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