How To Control temperature and Humidity In Poultry Houses

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.

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%.

According to the age of broiler chickens, the control of chicken house humidity can be roughly divided into two stages:

1. Before 10 days of age, the chicken house should maintain a high humidity. Generally, the humidity of the chicken house should reach 60%-65%. Chickens before 10 days old have small body weight and little excrement. The chicken house is often too dry and prone to the adverse effects of low humidity.

Commonly used humidification methods are: hanging wet curtains indoors; placing a water dish on the coal stove; placing wet straw handles in the house; spraying water on the walls, etc. For caged chickens, you can put a water tray in the top cage to humidify it, because the higher the temperature, the easier it is to evaporate and humidify!

2. After 10 days of age, the chicken house should be mainly dehumidified. Generally, the humidity of the chicken house is required to reach about 50%. As chickens grow up, their excrement increases, and the chicken house is often moist, prone to the adverse effects of high humidity.

Dehumidification measures include: strengthening ventilation; promptly replacing damp and clumping bedding; using highly hygroscopic bedding; preventing chicken drinking nipple from leaking, etc.

In addition to ammonia levels and temperature, it’s important to constantly monitor relative humidity levels for maximum affect.

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

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