The climate in poultry houses influences the wellbeing and health of humans as well as the birds. Respiratory, digestive and behavioural disorders are more likely to occur in houses in which the climatic conditions are not up to standard. The efficiency with which feed is utilised is related to the health status of the flock. Animals that are not healthy cannot be expected to perform optimally. The younger the animals are or the higher their production level, the more sensitive they become to the climatic conditions in the house. Climate can be defined as the sum of environmental factors which influence the functioning of man and animal.
The following factors must be measured at animal level.
House climate can be influenced by insulation of roof, walls and floor, ventilation, heating, cooling and lighting. The climate directly surrounding the birds is called the micro-climate (for example, chickens in a brooding ring). In fact, the micro-climate is the only thing that is of importance for the birds. It is possible that the climate in the house is acceptable but the climate at bird level is unsuitable. For example, CO2 is a heavy gas and CO2 levels at bird level can be much higher than at 2 m height. Another example is the brooding ring. The use of brooding rings means that the temperature of the house can be lower as long as the temperature at chicken level (under the brooder) is correct. This principle is applied in order to save on heating expenses. The advantages should be weighed against the disadvantages i.e. with brooding rings you can save on energy but often the labour to make and manage the brooding rings is more.
Layers are warm blooded (homeothermic) i.e. within a certain range, their body temperature is quite constant. On average, the body temperature of birds is between 41°C and 42.2°C. Body temperature is kept quite constant and is regulated by part of the chicken brain (the hypophyse). This part of the brain is comparable to a thermostat. Contraction and widening of blood vessels and the speed of respiration influence heat emission and retention which consequently influence the body temperature. It takes some time before heat regulating mechanisms start functioning in newborn animals and therefore they need a higher ambient temperature than adult animals do. Furthermore, the ratio between the surface area and weight of young animals is unfavourable and they do not have any fat reserves.
The comfort zone is defined as the temperature zone in which the birds are able to keep their body temperature constant with minimum effort. This temperature zone also depends on the feeding level and housing conditions. Behaviour of birds will change when temperatures rise to above the comfort zone as they will start to pant and change their body position. When temperatures are below the comfort zone birds will also change their body position and huddle together.
The thermoneutral zone is defined as the temperature zone in which the birds are able to keep their body temperature constant with the help of physical heat regulation . This temperature zone depends on feeding level and housing conditions of the birds and other factors. The lowest temperature in the thermoneutral zone is called the lowest critical temperature (LCT). If temperatures fall to under this temperature the bird will start to use feed energy to warm itself (i.e. maintain its body temperature) and will consequently consume more feed. The highest temperature in the thermoneutral zone is called the highest critical temperature (HCT). If the temperature rises above this temperature the birds can no longer dissipate their heat. They will start to consume less feed and production will drop as a result.
The highest and lowest critical temperature depend very much on:
When temperatures are not within the comfort zone, birds have several mechanisms which enable them to keep their body temperature constant without having to produce extra heat. This is referred to as physical heat regulation and factors that influence physical heat regulation include:
Another way in which poultry can regulate their body temperature is chemical heat regulation. When the ambient temperature is not within the thermoneutral zone the birds can:
The best instrument for measuring temperature is the animal itself. Assessing the temperature by observing the birds themselves should only be done when the animals are at rest, not when they are active or eating. Obvious indicators of unsatisfactory house climate are:
Measuring the temperature is the most common way of assessing the climate in a house. Such a measurement can give a lot of useful information and is not expensive or hard to do. There are several ways of measuring the temperature:
The temperature in a house is not uniform and therefore, there are several places where the sensor should not be placed (i.e. it should not be hung close to the wall or behind something which hinders the air flow) and should not be hung too high in the house. Furthermore, the location of the air inlet and heating equipment is important in determining the best position for the temperature sensor. It is best to place it as close to the animals as possible and in such a way that the fresh air passes the sensor before it reaches the animals.
The critical temperature for layers is 20°C. For every 1°C lower than 20°C, the birds require an extra 1.5 g of feed per day. The most efficient temperatures for layers are between 20 – 24°C. When temperatures rise above 24°C, shell quality and egg weight will reduce. The critical temperature for broilers and rearing birds is highly dependant on age.
The recommended house temperatures for poultry are given in the following table.
Table 1. Recommended temperatures for broilers
|1st week decrease
|2nd week decrease
|3rd week decrease
|4th week decrease
Note: These temperatures are recommended temperatures and should be adapted to local situations as necessary.
The following concepts are used to measure the humidity of air in poultry houses:
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.
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.
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%.
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:
Table 2. Gas Standards for European poultry houses
|<2500 ppm = 0.25 VOL%
|<25 ppm = 0.0025 VOL%
(1 volume % = 10,000 ppm)
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.
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.
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.
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.