The climate in poultry houses influences the wellbeing and health of humans as well as that of 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 that on bird level the climate 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. When we make use of brooding rings the temperature of the house can be lower as long as the temperature at chicken level is correct. This principle is applied in order to save on heating expenses. The advantages should be weighed against the disadvantages: 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 (homoiothermic) i.e. within a certain range, their body temperature is quite constant. On average, the body temperature of birds is between 41oC and 42.2oC. Body temperature is regulated by part of the brains (the hypophyge) and is kept quite constant. This part of the brains is comparable to a thermostat. Contraction and widening of blood vessels and speed of respiration influence heat emission and retention and consequently influence the body temperature. It takes some time before heat regulating mechanisms start functioning in newborn animals and so they need a higher ambient temperature than adult animals do. Furthermore, the ratio between the surface area and weight of young animals is unfavorable 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, they will start panting 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 a.o. 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 using feed energy to warm itself (i.e. maintain its body temperature). Consequently it will consume more feed. The highest temperature in the thermoneutral zone is called the highest critical temperature (HCT) If the temperature rises to above this temperature the birds can no longer dissipate their heat. They will start consuming less feed and its 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. Factors influencing 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 thermo neutral zone the birds can:
Assessing temperature by way of the animal The best instrument for measuring temperature is the animal itself. Animals show if the way they is housed is too cold or too hot. The animal functions as the sensor. Assessing the temperature in this way should only be done when the animals are at rest, not when they are active or eating. Things that can point to mistakes in 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:
Where should the temperature sensor be placed? The temperature in a house is not the same all over. There are several places where the sensor should not be placed e.g. it should not be hung close to the wall or behind something which hinders the air flow. Furthermore the location of the air inlet and heating equipment is important in determining a location for the temperature sensor. The sensor should not be hung too high in the house. 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. Animals that are kept at too low temperatures will have poorer technical results.
The critical temperature for layers is 20oC. For every 1oC lower than 20oC, the birds require 1.5 g of feed per day extra. The most efficient temperature for layers is 20 – 24oC. When temperatures rise to above 24oC, shell quality and egg weight go down. For broilers and rearer birds the critical temperature depends very much on age.
The Recommended house temperatures for poultry are given in the following table.
Table 1. Recommended temperatures for broilers and rearing
|1st week decrease||30oC|
|2nd week decrease||26oC|
|3rd week decrease||22oC|
|4th week decrease||20oC|
Note: These temperatures are recommended temperatures and should be adapted to local situation if necessary.
The following concepts are used to measure the humidity of air in poultry houses:
Example of relative humidity % If air with a temperature of 10oC 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 10oC) If the same air is heated without adding moisture until it has a temperature of 20oC the relative humidity will be 5.7/17.5 x 100 = 33%. So we can conclude 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 would be 4oC the relative humidity would be 5.7/6.4 x 100 = 89%. Conclusion: the warmer the air, the larger its moisture containing capacity.
Measuring humidity Relative humidity in poultry houses is measured to determine whether respiratory disorders are due to too high or too low relative humidity. Too high relative humidity can lead to condensation in the house. Humidity also influences the chances of survival for micro-organisms.
There are several ways of measuring the moisture content of poultry house air: – the psychrometer dry/wet bulb – the mechanical hygrometer. Measuring the moisture content air may be useful at times but due to the relatively higher costs of measuring the moisture content of air compared to measuring its temperature, the moisture content of air is not commonly measured as of yet. Controlling humidity Intense heating of house air when outside temperatures are low leads to low relative humidity in the house. The ideal relative humidity for poultry is 60-80%. If the relative humidity is too high, this may result in wet litter. A too low relative humidity results in a dusty house.
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 like carbon dioxide (CO2), and moisture (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.
(Noxious) gasses in poultry houses Harmful gasses in poultry houses are: – Carbon dioxide (CO2) The carbon dioxide in poultry houses large 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 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.
Table 2. Gas Standards for European poultry houses
|CO2||<2500 ppm = 0.25 vol%|
|NH3||<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. These tubes are necessary to determine the gas content. The tubes are filled with a chemical substance that discolors 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. Especially heating, lighting, and ventilation are negatively influenced by large amounts of dust. The dust in poultry houses mainly consists of skin particles, feathers, feed particles, litter and dried manure. Dust particles carry germs. Measuring dust The amount of dust in poultry houses is seldom measured as of yet. It can be measured in many different ways and requires quite a bit of equipment. It is not very clear what exactly needs to be measured. Is it necessary to measure the dust concentration in the air at a specific moment or do we want to know the average amount of dust present over a period of time. At present, it is deemed impossible to give practical advice on how to measure the amount of dust in houses because it is still unclear what exactly is worth measuring and because the methods available are either time-consuming and expensive or have not been proved to be reliable. Controlling dust levels 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. Besides, houses that are dirty promote ‘sloppy work’.
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 often leading to disease A simple way of determining the 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. In Formula 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 draft value is less than 0.8, if the draft value is more than 0,8 there is risk for drafts. If temperatures are higher than 25-30oC, air velocities of higher than 0.1-0.2 m/second will not have a negative effect but will just 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 pattern depends on the kind and control of ventilation within a house, the house width, the slope of the roof and the way the house is organized
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.
Both light intensity and lighting programmes have much influence on the technical results obtained. Lighting of poultry is so important that we have a special chapter on this subject. We refer to the section on lighting and lighting programmes for more detailed information on this subject. Light intensity can be measured with a luxmeter.
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