Chapter 7 - Air Quality
Chapter 7 - Air Quality
Air is a mixture of water vapor, nitrogen, oxygen, carbon dioxideand traces of other gases. Although its water vapor content is often less than 1% of the total, it is a major factor in determining the condition of the air mixture. This is due not only to the necessity of water in the life cycle but also to its great energy content when in vapor form. The latent heat in water vapor (the energy in the form of heat required to change water from liquid to vapor) is the largest of any common liquid. As a result the small amount of water vapor in the air mixture often contains the major part of the total heat energy of the mixture.
When allowed to accumulate to above acceptable threshold levels, air contaminants lead to poor air quality within the poultry house. Contaminants include solid particles; microorganisms such as bacteria, fungi and viruses; and gases such as ammonia, hydrogen sulfide, and carbon dioxide. These contaminants are always present to some extent in poultry house air, but can be minimized with a well-managed ventilation system.
The by-products of broiler production include heat, water, carbon dioxide and droppings, all of which are added to the environment inside the poultry house. When poultry droppings decompose in the presence of moisture and heat, ammonia is released into the air. Dust particles of dried droppings, feather and skin scales, and some feed become airborne. Microorganisms, including pathogenic bacteria and viruses, may be associated with the dust particles. Spores of harmful fungi such as Aspergillus fumigatus may also be present. The interaction of these various contaminants with litter conditions and temperature is the major cause of poor air quality and airsacculitis. In airsacculitis the lungs and air sacs become plugged with fluid. Affected broilers will gasp for air and often die suddenly. As a result, high mortality is often observed near market time so that after feeding a broiler for the majority of the growout period the broiler does not make it to the processing plant. Additional losses to the grower can be incurred by condemnation of carcasses during processing (see Chapter 4 for the various causes of carcass condemnation).
Ammonia is a colorless gas produced by microbial decomposition of nitrogenous compounds (protein, amino acids, and non-protein nitrogen) in the litter. Litter contains a diverse population of microorganisms that produce the enzyme urease, which converts the nitrogen into ammonia. Moisture, temperature, and pH of the litter also play an important role in the conversion of nitrogen into ammonia.
It is recommended that ammonia concentration be maintained at < 25 ppm throughout the growout for optimum broiler performance. When a person is constantly exposed to ammonia their sense of smell is adversely affected and their ability to detect ammonia decreases. With time, most growers are not able to detect ammonia by smell until the ammonia concentration in the broiler house has reached 50-60 ppm or higher. By this time, however, chick performance can be severely affected. In a study conducted at the USDA laboratory in Mississippi they noted that the difference in body weight from broilers exposed to 25 ppm vs. 50 ppm ammonia was 0.31 lb/broiler. With a flock of 25,000 broilers, this is equal to a loss of 7,750 lbs/flock. The best method to minimize ammonia during the growout is to properly ventilate. Litter amendments can be an effective management tool to reduce ammonia (see Chapter 14 for more information on litter amendments), but they are NOT a substitute for proper ventilation.
“The best method to minimize ammonia during the growout is to properly ventilate. Litter amendments can be an effective management tool to reduce ammonia, but they are NOT a substitute for proper ventilation.”
Particles that are very harmful to both poultry and humans are those that can be inhaled and deposited within the lower respiratory system. These are known as ‘respirable’ particles. Particles containing live microorganisms are known as ‘viable’ particles. Respirable particles and microorganisms are roughly 200 times smaller than a pencil point, having diameters less than 5 microns (a micron is one millionth of a meter). Most larger-diameter respirable particles are trapped by surfaces in the upper respiratory system of the nose and trachea. Particles with diameters smaller than 0.5 micron follow airflow patterns and are inhaled and are frequently deposited in the lower lung. If a respirable particle is a pathogenic microbe, a respiratory infection can occur. If the pathogen slips into the bloodstream (exchanged, as is oxygen), a serious system infection can occur. Endotoxins are released from dead bacteria and can produce many harmful symptoms in poultry and humans that inhale them. Endotoxins are especially troublesome because they resist sterilization and, therefore, cannot be easily cleaned from an environment.
Aerosol particles can have a range of effects on poultry. They act as irritant to the respiratory system and coughing is a response designed to remove them. Excessive coughing lowers the broiler’s resistance to disease. Aerosol particles collected inside the broiler increase condemnation of meat at the processing plant (see Chapter 4 for the various causes of carcass condemnation).
There are several methods that may be used to reduce aerosol generation or reduce aerosol concentrations. Proper ventilation is essential for bringing clean outdoor air into a poultry house to replace contaminated air. If houses are under-ventilated, aerosol concentration will continue to increase as more particles are produced by the birds without a means to dilute particle concentration.
Air in poultry houses should have less than 5 milligrams per cubic meter (mg/m3) dust at broiler level. Dust levels of 8 mg/m3 can be tolerated if the broilers are not being stressed by ammonia, heat, or the presence of respiratory disease agents. Good air quality management practices require heating and ventilating systems that provide a balanced environment. Poor respiratory health is the consequence of not providing this balance. Humidity and temperature also have an impact on air quality by influencing the survival of some pathogens and the severity of some diseases. Ventilation is an important consideration for controlling heat and humidity.
Particles that are very harmful to both poultry and humans are those that can be inhaled and deposited within the lower respiratory system. These are known as ‘respirable’ particles. Particles containing live microorganisms are known as ‘viable’ particles. Respirable particles and microorganisms are roughly 200 times smaller than a pencil point, having diameters less than 5 microns (a micron is one millionth of a meter). Most larger-diameter respirable particles are trapped by surfaces in the upper respiratory system of the nose and trachea. Particles with diameters smaller than 0.5 micron follow airflow patterns and are inhaled and are frequently deposited in the lower lung. If a respirable particle is a pathogenic microbe, a respiratory infection can occur. If the pathogen slips into the bloodstream (exchanged, as is oxygen), a serious system infection can occur. Endotoxins are released from dead bacteria and can produce many harmful symptoms in poultry and humans that inhale them. Endotoxins are especially troublesome because they resist sterilization and, therefore, cannot be easily cleaned from an environment.
Aerosol particles can have a range of effects on poultry. They act as irritant to the respiratory system and coughing is a response designed to remove them. Excessive coughing lowers the broiler’s resistance to disease. Aerosol particles collected inside the broiler increase condemnation of meat at the processing plant (see Chapter 4 for the various causes of carcass condemnation).
There are several methods that may be used to reduce aerosol generation or reduce aerosol concentrations. Proper ventilation is essential for bringing clean outdoor air into a poultry house to replace contaminated air. If houses are under-ventilated, aerosol concentration will continue to increase as more particles are produced by the birds without a means to dilute particle concentration.
The moisture content of air and floor litter impacts particle generation. If floor litter is excessively dry, air and bird movement tend to increase the amount of particles in the air. Misting systems may be used to moisten dry, dusty litter. Spraying vegetable oil has been shown to reduce particle generation in swine housing.
The most prevalent noxious gas in poultry housing is ammonia (NH3). Exposure to high concentrations of ammonia for extended periods has serious consequences on human and poultry respiratory health. Airborne ammonia is generated from the volatilization (vaporization) of decomposed uric acid in chicken manure. Microbial decomposition of uric acid to ammonia and carbon dioxide is a function of the litter moisture content, temperature, and pH, all of which influence the number and type of microorganisms (bacteria and fungi) present in the litter.
Poultry are adversely affected by high ammonia concentrations in a number of ways. Keratojunctivitis, an infection of the eyes, has been observed at concentrations of ammonia as low as 50 ppm. Ammonia blindness is seen five to seven days after the damage has been done. Long-term exposure to ammonia concentrations breaks down the broiler’s first defense against infection in the respiratory system. Ammonia-laden air destroys cilia in the trachea, which impairs mucus flow and thickens tissue around the alveoli. This damage makes broilers more susceptible to respiratory infections, such as Newcastle disease and air sacculitis. As previously indicated, ammonia concentrations ranging from 25 to 50 ppm over a 4-8 week period have been shown to reduce weight gains and feed efficiency.
