Climatic Requirements in Poultry Houses part A
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.
Air speed and air movement
Factors influencing climatic conditions and the birds’ micro-climate
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:
Read also: Factors that affect egg size
Physical heat regulation
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:
Tissue insulation – if birds have a layer of subcutaneous fat, they can afford to let their skin temperature drop. Only if the animals are fed properly can they deposit a subcutaneous fat layer when temperature decreases.
Feathers – feathers have an insulating effect and decrease the amount of heat that is lost to the environment.
Changing body position and huddling – birds can effectively regulate heat loss through body position. Heat loss can be minimised by huddling close together. In hot weather, on the other hand, the birds increase their body surface as much as possible.
Vaporisation of water – if temperatures are high, or extremely high, sensible heat loss is minimised and almost all heat will have to be lost as insensible (latent) heat. Latent heat loss is the heat lost from the body through the elimination of respiratory moisture.
Flow of blood through skin and mucous membranes – the flow of blood to the skin and mucous membranes can be controlled through the contraction and widening of blood vessels. The larger the flow of blood is, the more heat is lost.
Chemical heat regulation
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:
- Increase feed intake when the temperature is below thermoneutral zone
- Decrease feed intake when the temperature is above the thermoneutral zone.
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