July1 , 2022

Climatic Requirements in Poultry Houses part B



Climatic Requirements in Poultry Houses part B

Relative Humidity


The following concepts are used to measure the humidity of air in poultry houses:


Absolute humidity = grams of moisture present in 1 m3 of air.

Maximum humidity = maximum grams of moisture that can be present in 1 m3 of air at a given temperature.

Relative humidity = the relationship between the moisture content of the air and the maximum moisture content at the current air temperature expressed in percentages.

Example of relative humidity %

If the air temperature is 10 °C and contains 5.7 g of moisture, the relative humidity is 5.7/9.5 x 100 = 60%. (See the table 3 on absolute moisture content in g/m3 of air for the moisture content in air with a temperature of 10°C). If the same air is heated without adding moisture until it reaches a temperature of 20°C, the relative humidity will be 5.7/17.5 x 100 = 33%. So it can be concluded that heating air results in lower relative humidity. Conversely, cooling the air will result in a higher relative humidity e.g. if the same air was 4°C the relative humidity would be 5.7/6.4 x 100 = 89%. This demonstrates that the warmer the air, the greater its capacity to contain moisture.

Read also: climatic Requirements in Poultry Houses part A

Measuring humidity

Relative humidity in poultry houses is measured to determine whether respiratory disorders are due to too high or too low relative humidity. If the relative humidity is too high, condensation can accumulate in the house. This has a direct effect on the growth of micro-organisms.

Measuring and controlling humidity

There are several ways to measure the moisture content of the air in a poultry house, with the most common being the psychrometer dry/wet bulb or the mechanical hygrometer. Measuring the moisture content in the air may be useful, however there are higher relative costs involved in the measurement of the humidity compared to measurement of temperature alone. Due to this, the moisture content of air is not commonly measured.

Humidity is controlled by the intense heating or cooling of house air in response to the temperature outside the house. When outside temperatures are low, relative humidity in the house is low, which often results in dry dust circulating in the air within the house. If the relative humidity is too high, this may result in wet litter. The ideal relative humidity for poultry is 60-80%.

Air Composition

The most important components of air are nitrogen (N2, approximately 79%) and oxygen (O2, 20.3%). In addition to these main components there are several other gasses such as carbon dioxide (CO2), and water (H2O). Birds inhale O2 and exhale CO2 and H2O. True ‘lack of oxygen’ does not occur in poultry houses because animals can inhale sufficient oxygen even if the oxygen levels in the air are substantially lower than normal. What is called ‘lack of oxygen’ in practice is, in reality, often a combination of high CO2 concentration, high temperatures and high humidity.

Harmful gasses in poultry houses are:

Carbon dioxide (CO2) – The carbon dioxide in poultry houses largely originates from air exhaled by the birds. The CO2 content of the air is used to measure the effectiveness of ventilation.

Ammonia (NH3) – Ammonia is a product of bacteriological processes in the manure. It is easily bound to water. Ammonia is lighter than air and thus it rises in the air. The ammonia content of the poultry house air depends on ventilation, temperature, relative humidity and stocking density. High ammonia concentrations irritate the mucous membranes.

Hydrogen sulphide (H2S) – H2S is released when organic matter (protein) in the manure decomposes. It has an offensive smell (rotten eggs) and is a very dangerous gas. When the manure is stirred or removed from the pit, the H2S is released into the air. Even low concentrations of hydrogen sulphide in the air can be fatal for humans and animals. This is why it is important to ventilate at maximum capacity while stirring or removing the manure.

Carbon monoxide (CO) – Carbon monoxide is an odourless, very dangerous gas. It is the result of incomplete combustion due to a lack of oxygen (O2) in gas heaters (clean filters).

Sulphur dioxide (SO2) – Sulphur dioxide develops when oil is used as fuel. The cleaner the oil, the less SO2 is formed. The Maximum gas concentrations allowed in European poultry houses are in the table below.

Read also: Economic Benefits of Biosecurity in Poultry farming

Measuring gas content of air

A gas detector can be used to measure the gas content of the air. All measurements should be done at animal level. The device consists of a pump and its most important components are the tubes which are necessary to determine the gas content. The tubes are filled with a chemical substance that changes colour when air which contains the gas being measured passes through it. There are special tubes for determining the CO2, NH3, H2S, SO2 and CO contents of the air.

Measuring and controlling dust particles

Dust is harmful to the health of humans and animals and has a negative influence on the house climate. The functioning of equipment may also be seriously hampered by dust, including heating, lighting, and ventilation, and dust has also been shown to carry micro-organisms. The dust in poultry houses mainly consists of skin particles, feathers, feed particles, litter and dried manure.

The amount of dust in poultry houses is seldom measured. It can be measured in many different ways, however the processes are cumbersome and often require a multiple pieces of equipment as it is not known what is being carried in the dust each time the measurement is taken. It is currently difficult to give practical advice on how to measure the amount of dust, and what to measure for.

The amount of dust in a house depends on many different factors. These include temperature, relative humidity, type and age of the animals, type of litter used, feeding system, hygiene, etc. Proper maintenance of poultry houses and regular cleaning creates more comfortable conditions for animals and better working conditions for humans.

Air Movement And Airspeed

Whether or not birds are comfortable is very much influenced by air velocity and air temperature. Young animals are more sensitive to these factors than older, heavier animals. Taking into consideration the recommended temperatures, the air velocity at animal level is allowed to vary between 0.1 and 0.2 m/second. If house temperatures are low, the animals experience higher air velocities as a (severe) draft which can lead to disease. A simple way of determining the (negative) effect of drafts is the ‘draft value’.

The draft value is the temperature difference between the house air and the incoming air (in degrees Celsius) multiplied by the airspeed in m/sec ( D= (OT – IT) X S D = Draft value OT = Outside Temperature IT = Inside temperature S = airspeed at bird level in m/sec). The standard for the draft value is a value less than 0.8. If the draft value is more than 0.8 there is risk for drafts to occur in the poultry house. If temperatures are higher than 25-30°C, air velocities of higher than 0.1-0.2 m/second will actually have a positive effect and help to cool the animals.

The air movement pattern within a house is easier to control in this way as the influence of air velocity and outside temperature are less. It is not possible to give rules for the air movement pattern within a house because the air movement patterns depend on the ventilation within a house, the house width, the slope of the roof and the way the house is organised.

Measuring air velocity

Air velocity can be measured using an anemometer. The air movement pattern within a house can be made visible by using a smoke generator or smoke powder.

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