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Mike Czarick, Brian Fairchild and Brian Jordan

Poultry Science Department, University of Georgia, U.S.A.

It is essential to maintain a good air quality overnight in order to avoide health problems in broilers and this must be considered a permanent task

One of the most important variables which must be controlled and should be kept as low as possible is ammonia gas

High ammonia levels can paralyze and/or harm cilia in the trachea, which are vital as part of the bird’s defense against pathogens and physical agents

Figure 1. Cilia in an intact trachea.

Cilia from the trachea are projections in the form of microscopic fingers on the trachea epithelium

On the trachea cilia there is a thin layer of mucous secretion having the function of capturing pathogens which may be physically transported in the dust of barns or aerosols. These cilia have a wave-type movement the purpose of which is to move pathogens and other particles towards the oral cavity so that they may be swallowed and eventually destroyed by the digestive secretions.

However, if the cilia are paralyzed or damaged, the mucous secretion -altered due to high ammonia levels-would allow the pathogens to more easily reach the lower respiratory tract. They would start replicating in the bronchi causing avian diseases (e.g. bronchitis). But also, these pathogens may destruct the epithelial cells and their cilia facilitating infection with secondary pathogen agents (e.g. E. coli).

Ammonia peaks are potentially more harmful than constant moderate levels thereof

We tend to focus concerns on the issue that implies constant and high ammonia levels, but it is relevant to consider that research has demonstrated that, sometimes, short periods of high ammonia level may be as harmful or more harmful than constant moderate levels thereof.

Therefore, we need to ensure that ammonia levels are maintained as low as possible not only during the day, but also overnight. During the coolest part of the year, air quality in re-breeding (breeding) tends to be fairly consistent during the day, with a generally common standard for most producers:

  • air exchanges are determined by the minimum ventilation mode
  • Minimum ventilation is controlled by means of predetermined settings- on computers or controllers.
  • Computers control time ventilation over 24 hours during the breeding stage


Since chicks do not produce yet a large amount of metabolic heat, and external temperatures are considerably lower than predetermined temperatures inside the barn, said barn never goes into cooling mode, which would normally increase the rate of ventilation.

When ammonia levels are low in the afternoon, it is generally assumed that they will continue being low overnight (Figure 2). Unfortunately, the equilibrium described is not applicable to later periods in the growth cycle.


As birds grow older, the amount of fresh air introduced in the farm during cold seasons, is not only determined by minimum ventilation settings, as is the case during the initial farming phase. As birds become old they produce more heat, so the farm gets more temperature.

According to set temperature rule, the barn goes into cooling mode. Consequently, vents will work more during the day to keep an adequate temperature in the farm (See Figure 3).

Figure 3. Internal and external daily temperatures; and ammonia levels for a 3 week-old chicken barn.

As we can observe in the graph, during the day, the external temperature is less cold than overnight and more contribution will be necessary to cool a barn than at night since night air is typically cooler.

As a result, daytime ventilation may often be two to three times higher than night-time ventilation and air quality may be significantly better in the daytime than at night

The daytime variation in air quality may be difficult to manage by producers. In most cases, air quality is evaluated during the day, when birds receive the care of farm workers. If ammonia levels seem acceptable, then, no adjustments are made to the rate of ventilation. This is precisely the problem as regards air quality during nighttime ventilation.

  • The very fact that air quality seems acceptable during the day does not mean that this air quality will still be appropriate overnight.

Potentially harmful ammonia nighttime levels may be reached.

  • We must take into account that ammonia concentrations in the barns are generally proportional to ventilation rates.

If the ventilation rate is reduced by 50% at night because minimum ventilation vents operate by time and not by temperature, ammonia concentration shall be twice as high at nighttime than at daytime

If the operation of air vents at night is only one third of their daytime activity, ammonia concentration may reach 3 times the concentration achieved during the day (See Figure 3).


Even though barn temperatures seem right, ammonia levels are lower at  20ppm, relative humidity and dust concentration are low and everything looks ideal.

However, mortality continues elevating and birds are showing the first signs of respiratory disease.

Air quality varies dramatically from daytime to nighttime, and this may explain some bird health problems

There must be awareness that, in many barns and farms, there is always a certain potential of disease challenge. Birds challenged 24 hours a day, 7 days a week and 52 weeks a year are at risk due to some type of challenge. This is not much different to respiratory challenges which people suffer during cold seasons. Most of the time, the immune system of birds may deal with these challenges although its magnitude tends to increase during cold seasons.

Pathogen concentration in barns tends to increase as ventilation rates decrease

Pathogen concentration, combination of an increase in the barns tends to increase as ventilation rates decrease – as in the case of people, since they tend to stay longer inside buildings and not outdoors-.

The situation may be critical at night when temperatures decrease and the rate of ventilation decreases to its lowest levels. At the same time, maximum pathogen and ammonia concentrations are reached.

If this happens for eight hours at night and for multiple consecutive nights, this is all that is required in order to trigger a respiratory issue.



Ideally, ammonia concentration and barn temperature should be constantly registered 24 hours a day, but this is impractical. A precise ammonia meter as illustrated in this article costs about  $10.000 and thousands of dollars per year to maintain it. An alternative would be to go in the barns each night at 3 a.m. in the morning and this is also impractical.

Figure 4. Internal and external temperature, ammonia, relative humidity for a three week-old bird barn (data recorded from November 3 to 4 in northern latitude)

In reality, we can have a very good idea of the situation at night if we measure relative humidity in the barns. Although relative humidity is basically a measure of humidity levels in the barns, it is also an indication of other important variables affecting the quality of air as ammonia and carbon dioxide.

Relative humidity is an indication of air quality as are ammonia and carbon dioxide

calidadaire9Another option would be to use some type of portable humidity registration unit. In our lab, we use the Onset UX100-023, however some other equivalent unit may be used. (See Figure 5).


This unit is capable of registering temperature and relative humidity every 5 minutes for the complete duration of the fattening cycling of chickens, or for a 30 day period if the registration of data every minute is desired.

Maximum and minimum relative humidity limits may be decided and programmed and if reached, then, adjustments may be made in a very simple way (See Figure 6).

A relative humidity sensor for a controller in barns or a temperature and humidity registration unit such as  onset uX100-023 cost about  $200.00 or $300.00 dollars. Although this seems excessive, information which may be obtained through its use for data directly or indirectly related to air quality at night is invaluable.

Finally, we can do a very good job providing the ideal environment for birds during daytime but, if birds get ill because we ignore what happens in the barns at nighttime, losses may easily and readily reach thousands of dollars for the producer and for the poultry company





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