Relative humidity...The best measure of overall air quality in the poultry house - UGA Poultry House Environmental Management and Energy Savings (2024)

Knowing how much air to ventilate in cold weather is critical to a poultry farmer's bottom line. Insufficient ventilation can lead to poor air/waste quality, resulting in health and performance problems for the birds. Too much ventilation can lead to drafts, dusty conditions and high heating costs. To best determine the minimum operating time for ventilation fans, business managers should ideally monitor the three most important air quality variables: carbon dioxide, ammonia and relative humidity. Carbon dioxide is product...used by both the birds and the home's heating system. High carbon dioxide concentrations can lead to lethargic chicks and reduced weight gain and should therefore be kept below 5,000 ppm (ideally below 3,500 ppm). High ammonia concentrations can lead to poor feed conversion, reduced weight gain and increased susceptibility to disease. To maximize bird performance and health, ammonia concentrations throughout the flock should be kept below 30 ppm (ideally below 20 ppm). Last but not least, relative humidity should be kept between 50 and 70%. Lower relative humidity usually leads to a dusty house and high heating costs, while higher relative humidity can lead to wet waste and high ammonia concentrations. By having meters that measure carbon dioxide, ammonia and relative humidity, business managers can set their minimum ventilation fans to ventilate just enough to maintain good air quality without overventilation and increasing heating costs.

As you might suspect, the problem with measuring all three air quality variables is cost. A reasonably accurate and reliable carbon dioxide meter usually costs between $300 and $500. Most ammonia meters used in the poultry industry cost between $500 and $1,000. The problem is that their accuracy is questionable, requires regular calibration, contains sensors that typically need to be replaced annually, and generally cannot be left in the home for long periods of time. On a more positive note, monitoring relative humidity is a fairly simple and inexpensive proposition. A reasonably accurate relative humidity meter that can record daily maximum and minimum relative humidity typically costs between $50 and $150. A relative humidity sensor can be added to most controllers for less than $300 and allows the controller, if the manufacturer wishes to make continuous changes to the minimum ventilation rates to ensure that the relative humidity remains within a certain range.

While it would be helpful to have access to all three types of meters, it is realistic that the only meter that farm managers need to assess overall air quality in the poultry house is a meter that measures relative humidity. This is because ammonia and carbon dioxide concentrations in most of a herd tend to follow relative humidity closely in cold weather. That is, when relative humidity is high, carbon dioxide and ammonia levels will tend to be high. When relative humidity is low, carbon dioxide and ammonia levels will also be low. The close relationship between ammonia, carbon dioxide and relative humidity tends to be strongest in older birds and weakest during the first two weeks of the flock. This is due to the significant amount of carbon dioxide produced by most heating systems and the use of waste treatments, which can result in a situation where relative humidity is low and carbon dioxide is high, or relative humidity is high and ammonia concentrations are low. low.

The close relationship between carbon dioxide, ammonia and relative humidity can be seen in Figures 1 and 2. Air temperature/Rh, carbon dioxide and ammonia were continuously monitored in a fully enclosed 40' x 500' broiler house. Measurements were taken every 15 minutes beginning when the birds were 18 days old and continuing until the end of the flock at 39 days. Carbon dioxide and ammonia concentrations were measured using a high-precision photoacoustic gas analyzer ($40,000), while house temperature and relative humidity were monitored using an environmental controller for poultry houses (Choretime II).

During the study period, ammonia and carbon dioxide concentrations remained within acceptable limits when relative humidity was 60% or lower. Conversely, when relative humidity was above 70%, ammonia and carbon dioxide levels tended to rise to what would generally be considered potentially harmful. There were of course exceptions. For example, in Figure 3, the relative humidity on December 21 and 22 was high because it was raining, but carbon dioxide and ammonia levels were relatively low because the outside temperatures were quite warm and some fans were running. to maintain the right temperature in your home. But the fact is that for the most part, relative humidity of 70% or more is a good indicator that minimum ventilation needs to be increased if optimal growing conditions are to be maintained.

It is important to note that most studies on the effects of ammonia, carbon dioxide and relative humidity on bird performance have been conducted with birds exposed to high levels of one, and not two or three, at a time. The problem is, as shown in Figures 1, 2 and 3, that this is not common in poultry houses. When ammonia is high, carbon dioxide and humidity are also high. It is entirely possible that the combination of high carbon dioxide, ammonia and relative humidity could have a more detrimental effect on bird performance than when just one of the three is high. Additionally, if air exchange rates are too low (as indicated by high relative humidity, carbon dioxide and ammonia levels), pathogen levels in a home are also likely to be higher than normal. The combination of low indoor air quality and higher than normal pathogen levels can most likely lead to increased susceptibility to disease. It begs the question... How many of our production problems could be avoided if we simply used relative humidity as a basis for adjusting minimum fan run time?

Although there is no exact relationship between relative humidity, ammonia and carbon dioxide, the relationships are consistent enough to indicate that when a relative humidity of 60% or lower is maintained, air quality generally remains within acceptable limits. Conversely, a relative humidity of 70% or higher is often a fairly accurate indicator of poor air quality. During the incubation period, relationships are not as strong, so producers should be aware that ammonia or carbon dioxide levels may still be at harmful levels even when relative humidity is below 60%.

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