By- Dr Manish Kumar, TVO
Just before arrival of Mansoon till rainy seasons ,the condition of poultry birds, may be layers or broilers , become very alarming in India due to the ill effect of the relative humidity leading to drop in production and mortality in the flock.
The effect of rising ambient air temperature on the physiology of poultry cannot be considered in isolation because when high temperature is accompanied by high humidity (over 75 per cent) the birds will rapidly succumb and die through heat prostration.
Birds do not possess sweat glands but instead lose water by evaporation from facial appendages and through panting. However, when humidity is high the poultry house atmosphere of the house is saturated with water vapour, liquid water excreted by the birds fails to evaporate with its usual natural cooling effect. Air movement, natural or artificial, alleviates the situation by taking air, saturated with water vapour, away from the birds and thus allowing the water excreted from their bodies to evaporate.
Feeding, ingestion and digestion all generate heat. While this extra heat is useful for birds raised in low temperature conditions, it will simply aggravate heat stress in birds during periods of at temperatures. Not surprisingly, birds react to high temperatures by reducing their feed intake.
This clearly poses the problem of whether accompanying losses in production – eggs decrease in size, weight and shell strength – are due to heat stress per se or lack of energy-rich feed ingredients, proteins and/or vital nutrients and vitamins. In fact loss of productivity with increasing temperature over and above 26 °C is due to a combination of both.
The higher susceptibility of poultry, compared with other livestock, to heat stress is because avian body temperature is much closer to the point of ‘heat death’ than ‘cold death’. The normal body temperature of birds is 41.2 to 42.2 °C which is just 4 to 5 °C below the point at which enzyme proteins start to denature with the complete collapse and failure of body metabolism. This situation is clearly compounded by birds’ lack of sweat glands and their inability to operate a natural and intrinsic cooling system.
Basic passive measures aimed at keeping poultry cool rely on the design and location of the poultry house. They include orientation and pitch of the roof to minimise direct sunlight falling on the house, planting of shade trees around the house and whitewashing the walls and roof for maximum heat reflection. Making the most of maximum natural air movement by leaving the house sides open is the most common feature of poultry houses in hot climates, although this in itself demonstrates the ultimate futility and complete inflexibility of trying to custom-design poultry houses to specifically combat heat stress.
Having open sides allows rainfall to enter during the hot wet season and is completely counterproductive in situations where there are big diurnal fluctuations in temperature or climates where summers are very hot and winters correspondingly cold. Birds suffer all round discomfort including cold and chilling for significant periods. Poultry producers’ policy should be to design and build a house for the efficient management and production of the birds, and then add a custom-designed, active cooling system.
The simplest active cooling system is based on electrically-operated air circulation fans installed inside the house. The basic drawback of using a ventilation system based only on air circulation and is that it just moves around the ‘in-house’ air without removing its intrinsic heat.
On the plus side they are useful for broilers raised on the floor, from which rate of heat convection loss is maximised by increasing the speed or air movement at bird level by installing extra fans. Research suggests that an allocation of 1 circulation fan for every 10-15 metres (m) along the house mounted 2 m off the floor and aimed slightly downwards will achieve the best results, In addition, movement of by the circulation fans make the broilers stand up, thus breaking up the layer of stagnant hot air which tends to form around birds.
Use of evaporative cooling takes the heat out of the situation by utilising a basic law of physics. For liquid (including water) to evaporate it must be supplied with energy in the form of heat, otherwise called the Latent Heat of Vapourisation. Water sprayed into the house as a mist or a fog is composed of very small droplets which readily and rapidly evaporate. And in doing so absorb heat from the house environment and thus lower the temperature inside the poultry house.
Misting systems are useful but the droplets at around 50 µm in diameter will quickly sediment before they can evaporate, to cause damp and mouldy bedding material with discomfort to the birds and encouragement for pests, parasites and disease.
Fogging systems which utilise much smaller droplets of 10 µm or less avoid these problems. However, these very small droplets can enter the ‘airways’ of the birds and lodge in the depths of the respiratory system to cause health problems. The only way for producers to obtain the real and rapid benefits of evaporative cooling, without liquid moisture problems, is to employ a pad cooling/tunnel air system.
Pad cooling/tunnel air systems comprise a continually wetted filter pad at one end of the house and a powerful extractor fan at the other. Air continually drawn out from within the house by the extractor fan is replaced by air pulled in through the wetted filter pad. Water fogged onto the pad in ultra-fine droplets ‘flash evaporates’ taking heat from air drawn into the house. The net result is a continuous tunnel of cool air passing through the house to maintain the birds in a state of perpetual comfort. Birds receive the benefits of evaporative cooling without the problems associated with water droplets in the house atmosphere.
With for instance an outside air temperature of 35° C, a high efficiency cool pad system will reduce house temperature down to 28° C, with a further 5° C drop to a comfortable 23° C due to the wind-chilling effects of the tunnel airflow. Producers with a pad-cooled house but still experiencing hot weather and heat stress problems should not automatically jump to the conclusion that that the pad system is at fault. Dirty shutters can cut airflow by 30 per cent and a 15 per cent fan belt slippage means an equivalent reduction in airflow. Producers should ensure that the house is air- tight, all air leaks are sealed and the tunnel curtains are not blocking the flow of air into the house.
The nozzle tips are the most important part of any evaporative cooling (misting/fogging) system, whether designed to be conventional (overhead) or based on the cool pad design. The nozzle tips are by far the smallest components of the system, but will ultimately determine the characteristics of the mist/fog spray.
The nozzle is the final component of the system and through which the water passes to be broken up into droplets according to its interior design, orifice and water pressure. As such it determines flow rate, droplet size and droplet size distribution. These characteristics, as well as material technology and the arrangement (size, density and spacing) of nozzles in the overhead system or on the cool pad, determine its success or failure in reducing house temperature to acceptable levels.
Installation of misting/fogging nozzles offers poultry producers the opportunity for application within a wide pressure range of 3 to 14 bar (40 to 200 psi) and fine droplets of less than 50 µm, which are considered optimum for rapid evaporation and effective cooling.
Misting and fogging nozzles may be installed in traditional overhead atomiser (nozzle) arrangements using PVC pipe and solvent-welded fittings with 3 m between each atomiser line, 2.5 to 3.0 m between atomisers in the line and a separation distance of 3 m between atomisers and the house eaves (roof rafters or struts).
Nozzle tips are most effective when used as the atomising element in a cool pad/tunnel air system for poultry house cooling. Banks of fogging nozzles are installed so that they are deployed 450 to 600 millimetres (mm) away from the pads, with spray directed at the pads so that they are permanently and uniformly wetted for maximum performance and long life.
Pad designers recommend fogging nozzles with a flow rate of 3.8 litres per hour and a spray angle of at least 80 degrees. A pad of 1.8 m in height should be provided with three rows of fogging nozzles on pipes 450 mm apart with a separation distance of 450 mm between individual nozzles along each pipe.
Several factors including the thickness of the pads used will determine cooling efficiency level obtained. A carefully worked out nozzle arrangement so that there are no dry spots on the pad, as well as regular cleaning and flushing of the pads to avoid plugging (blockage), is vital. Low-level siting of cool pads means that the nozzles are easy to clean and change.
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.
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%.
In addition to ammonia levels and temperature, it’s important to constantly monitor relative humidity levels for maximum affect.
By ventilating poultry houses for relative humidity (RH) level of 50-70% you can prevent moisture build-up and litter stickiness around the drinker/feeder lines and the sidewalls which will help:
• Minimize ventilation during brooding
• Prevent ammonia formation
• Lower incidence of paws lesions
• Save on fuel costs
Maintaining ideal RH levels is easier than you think. Simply:
1. Check for air leaks around the inlet machines and check for drafts along sidewalls.
2. Refrain from tilling litter and set your de-caker only deep enough to remove cake without disturbing the deeper litter. Learn more about proper de-caking here.
3. Pre-heat before bird placement to reach 94°F evenly across the entire litter surface and 2-3 inches deep into the litter.
4. Ensure proper warming and mixing across the ceiling by checking static pressure.
5. Check RH levels in the morning and add fan time if levels rise about 70%.
Acquiring satisfactory humidity levels in the environment in which eggs are hatched makes embryos lose water from their inside to the outside through steady evaporation.
Each egg has diverse qualities, for example, size, thickness, the amount of pores and shell conductance. For instance, in older flocks the conductance and size of the egg are more prominent, consequently they ought to be hatched with higher humidity. It ought to be recollected that thousands of eggs are taken care of so they ought to be assembled in a way that their qualities be as similar as possible, by flock, age and days in storage.
When there is weight reduction, the hatch is troublesome, the chick requires more energy consumption to have the capacity to incubate, making a weaker chick be born. On the other hand, an egg that has the perfect weight reduction will encounter a simpler hatch and will invest less efficient energy. Weight reduction is affected by moisture in the air, as well as by temperature. As the temperature increments, brought about by embryonic advancement and development, evaporation increases through the shell.
A very much fixed single stage machine helps the humidity increase quicker than CO2, which is the reason why the damper can be controlled by humidity. When there are eggs from old breeders the damper will open earlier and when a young flock with low fertility is set, the damper will open later, adjusting to the attributes of the flock that is in the setter. To obtain good weight reduction, classification and request must be kept up when dealing with the eggs in the cool room, checking chick quality, measuring weight reduction and changing it as indicated by the results. Satisfactory weight reduction offers benefits for embryonic advancement and in the hatching process, which brings about energy investment funds during the incubate, and in getting a chick with incredible potential.
Reference:On request.
