Air quality management in poultry houses represents one of the most critical factors determining both animal welfare and economic success in modern broiler production. The delicate balance between oxygen availability and the control of harmful gas emissions directly impacts productivity, making it essential for producers to understand and implement effective air quality strategies.
The atmosphere within poultry houses contains a complex mixture of gases that can either support or hinder bird performance. Oxygen serves as the foundation for metabolic processes, while emissions including ammonia, hydrogen sulfide, carbon dioxide, and particulate matter pose significant health risks to both animals and workers. Environmental factors such as temperature, humidity, and airflow patterns influence how these compounds distribute throughout the facility, making comprehensive site assessment crucial for successful poultry operations.
Modern approaches to air quality management encompass both preventive and mitigation strategies. These range from dietary modifications using natural additives to reduce ammonia and methane production, to advanced technological solutions including biofilters and air scrubbers for treating exhaust air (Carey et al., 2004). Successfully balancing this atmospheric mixture remains a cornerstone of profitable chicken meat production.
The Critical Role of Oxygen Supply
Fast-growing modern broiler hybrids demand substantial oxygen levels to support their accelerated metabolic processes. Research by Beker et al. (2003) provides compelling evidence of oxygen’s impact on growth performance, revealing dramatic differences in weight gain based on atmospheric oxygen concentration.
In their comprehensive study, broiler chickens exposed to varying oxygen levels showed striking performance differences. At 14 days of age, birds maintained at 12% oxygen concentration achieved only 138 grams of weight gain, while those at normal atmospheric levels (20.6% oxygen) reached 371 grams. The progression was clear: 14% oxygen yielded 287 grams, 16% produced 353 grams, and 18% resulted in 356 grams of weight gain.
These findings translate to significant production losses. Broilers reared under reduced oxygen concentrations of 12%, 14%, 16%, and 18% experienced weight reductions of 62.8%, 22.6%, 4.9%, and 4.0% respectively, compared to those raised under normal atmospheric conditions (Beker et al., 2003). The relationship between oxygen availability and growth performance is unmistakably linear, emphasizing the fundamental importance of adequate ventilation systems in maintaining optimal oxygen levels.
Managing Particulate Matter: The Dustiness Challenge
Airborne particulate matter (PM) concentrations in poultry houses can reach levels 10 to 100 times higher than outdoor environments, creating significant health concerns for birds and workers alike. Understanding the sources and composition of these particles is essential for developing effective control strategies.
Sources and Composition
Particulate matter in broiler houses originates from multiple sources, with manure comprising the largest fraction at 72.1%, followed by feathers at 21.3%, wood shavings at 5.8%, and ambient particles at 0.7% (Wicklin and Czarick, 1997). These particles are categorized by size, with PM10 (particles under 10 micrometers) and the more dangerous PM2.5 (particles under 2.5 micrometers) being of particular concern due to their ability to carry microorganisms and toxins deep into respiratory systems.
The unique semi-open structure of avian lungs makes birds exceptionally susceptible to dust-related irritation. Several factors influence PM concentrations, including bird species, stocking density, management practices, lighting duration, and environmental conditions. Notably, PM levels increase with bird age due to greater feather production and activity levels, while daily feeding times and light exposure periods create temporary spikes in airborne particles (Wang et al., 2023).
Comprehensive Mitigation Strategies
Effective PM management requires a multi-faceted approach addressing emission sources, air filtration, and environmental controls:
Housing System Selection: The choice of housing system significantly impacts dust levels. Cage-based systems consistently demonstrate lower PM concentrations compared to floor-based or aviary systems. Research indicates that dust concentrations in aviary systems can exceed those in cage systems by 6 to 9 times, primarily due to increased litter disturbance and bird activity (Liu et al., 2015).
Liquid Application Systems: Spraying water, acidic water, or oil-water combinations can reduce PM10 and PM2.5 emissions by 18% to 64%. However, proper dosage and pH control are crucial, as excessive water application may inadvertently increase ammonia emissions (Winkel et al., 2016).
Bedding Material Optimization: The selection of appropriate bedding materials substantially impacts particle generation. Alternatives such as peat or clay pellets produce less dust than traditional wood shavings or straw. While reusing litter may increase PM emissions, topping existing litter with fresh bedding can reduce concentrations by up to 40% (van Harn et al., 2012).
Advanced Filtration Technologies: Sophisticated filtration systems, including dry filters, water filters, and biofilters, demonstrate high efficiency in PM removal. Acid scrubbers show particularly impressive results, reducing PM10 by 61-93% and PM2.5 by 47-90% (Patterson, 2005).
Electrostatic Ionization: This technology charges airborne particles, causing them to precipitate onto surfaces. Studies demonstrate reductions of up to 94% for PM and 96% for airborne bacteria (Winkel et al., 2016).
Environmental Controls: Proper ventilation remains fundamental for diluting and removing particles. High ventilation rates, especially during warmer periods, significantly reduce PM concentrations. Additionally, adjusting lighting schedules to include dark periods decreases bird activity and associated dust production.
Facility Hygiene: Regular and thorough cleaning protocols, including comprehensive vacuuming and power washing between production cycles, provide a simple yet effective foundation for dust control.
Ammonia: Understanding the Primary Concern
Ammonia emissions represent perhaps the most significant air quality challenge in broiler production. Understanding the biological processes behind ammonia formation provides the foundation for effective control strategies.
The Formation Process
Ammonia production begins with uric acid, the primary end product of protein and nitrogen metabolism in poultry. Microorganisms in poultry excreta decompose both uric acid and undigested proteins through enzymatic processes, particularly involving the enzyme uricase. This breakdown process thrives under specific conditions: temperatures above 20°C, pH levels between 7 and 9.0, and litter moisture content of 40-60%.
Unfortunately, these same conditions that promote uric acid decomposition also favor the growth of pathogenic microorganisms including Salmonella and E. coli. This dual challenge requires careful management to control ammonia emissions while maintaining flock health (Carey et al., 2004).
Factors Influencing Ammonia Production
Litter and Manure Management: Management practices significantly impact ammonia levels. The choice between built-up litter and fresh litter, litter age, cleaning frequency, housing structure design, and manure accumulation time all influence emission rates. Poor management practices and prolonged litter use correlate strongly with elevated ammonia concentrations.
Physical and Chemical Properties: Several key factors determine ammonia release rates (Konkol et al., 2022):
– pH Levels: Minimal ammonia release occurs below pH 7.0, while rapid release begins above pH 8.0, making pH management crucial for emission control.
– Moisture Content: High humidity levels accelerate microbial breakdown of uric acid, directly increasing ammonia production rates.
– Temperature: Elevated litter and air temperatures promote ammonia emissions through reduced gas solubility and enhanced microbial activity.
– Nitrogen Content: Dietary protein levels directly influence litter nitrogen content and subsequent ammonia production.
Environmental Conditions: House management significantly affects ammonia concentrations:
– Ventilation Rates: Insufficient ventilation allows ammonia accumulation, while appropriate airflow dilutes concentrations and can help stabilize manure through moisture reduction.
– Seasonal Variations: Cold weather combined with reduced ventilation creates high concentration conditions, while warmer temperatures may increase emissions from litter itself.
– Humidity Control: High relative humidity, whether environmental or from cooling systems, accelerates ammonia production.
Flock Characteristics: Bird-related factors contribute substantially to ammonia production:
– Dietary Composition: High-protein diets result in excess nitrogen being metabolized into uric acid and subsequently ammonia.
– Bird Age and Weight: Ammonia emissions correlate strongly with bird maturity, increasing over time as heavier birds produce more uric acid per unit area.
– Stocking Density: Higher bird densities concentrate uric acid excretion, leading to elevated emission rates.
Proven Mitigation Strategies
According to Swelum et al. (2021), effective ammonia control requires a comprehensive approach:
Nutritional Management: Providing precisely balanced diets that meet nutritional requirements without excess protein represents the most fundamental strategy. Reducing dietary protein by 3-5% for broilers can significantly decrease nitrogen excretion without compromising performance. Avoiding high-fiber diets that contribute to wet litter problems further supports emission control.
Space Management: Ensuring adequate floor space prevents overcrowding-related wet litter problems, a major contributor to ammonia production.
Ventilation Systems: Well-designed ventilation systems rapidly remove ammonia while maintaining appropriate temperature and humidity levels.
Environmental Controls: Maintaining comfortable temperatures, particularly during winter months, requires careful balance to avoid compromising ventilation effectiveness.
Water System Management: Strategic placement and regular maintenance of watering systems prevent leaks that increase litter moisture and promote ammonia formation.
Litter Management: Maintaining litter moisture between 15% and 25% proves essential, as higher levels dramatically increase ammonia release. Regular monitoring and replacement of caked litter with fresh, dry material, combined with maintaining litter pH below 7.0, provides significant emission reduction.
Chemical Amendments: Various compounds including alum, liquid alum, aluminum chloride, and sodium bisulfate can be added to poultry manure to regulate ammonia emissions.
Nutritional Supplements: Adding antioxidants, probiotics, and prebiotics improves nutrient digestibility, reducing undigested protein excretion and subsequent ammonia production.
Phytogenic Additives: These natural feed additives enhance digestibility and beneficially alter intestinal microflora, reducing undigested nutrient excretion and significantly lowering ammonia volatilization.
Carbon Dioxide Management
Carbon dioxide concentrations in broiler houses fluctuate based on multiple factors, with levels typically increasing during the brooding period due to gas burner operation. Primary influences include bird number and size, ventilation rates, heating system usage, and individual bird characteristics such as feed consumption, diet composition, activity level, and age.
While young chicks tolerate CO2 levels up to 4,000 ppm without adverse effects, much higher concentrations become dangerous. At 118,000 ppm, birds exhibit gasping and respiratory distress, while 174,000 ppm proves lethal. Laying hens exposed to concentrations between 20,000 and 50,000 ppm for extended periods show respiratory distress and decreased appetite (Reece and Lott, 1980).
Excessive CO2 levels alter metabolism by reducing plasma thyroxine and glycogen concentrations while affecting bird activity, behavior, and production performance. These findings underscore the critical importance of maintaining appropriate CO2 levels for optimal bird health, welfare, and productivity (Burggren et al., 2015).
Hydrogen Sulfide: The Silent Threat
Hydrogen sulfide (H2S) represents a significant but often overlooked air quality challenge in poultry production. This greenhouse gas primarily originates from anaerobic decomposition of sulfur-containing amino acids, including cysteine and methionine, present in poultry manure. Broiler operations typically generate higher H2S emissions compared to other livestock systems, with average concentrations around 0.33 ppm (Saksrithai and King, 2018).
High H2S concentrations pose serious health risks. Levels as high as 4,000 ppm can cause rapid respiratory rate increases and death within 15 minutes (Klentz and Fedde, 1978). Even lower concentrations can decrease carcass weight and increase moisture loss from breast and thigh meat. Young birds (0-3 weeks) show greater susceptibility to H2S exposure compared to older birds (4-6 weeks), which can withstand higher concentrations (Chi et al., 2018).
Management Strategies
Effective H2S reduction employs both pre-excretion and post-excretion approaches:
Pre-excretion Methods: Dietary modifications form the foundation of prevention, including reducing crude protein levels and incorporating beneficial additives such as distiller’s dried grains, chlorine dioxide, and phytobiotics like Punica granatum L. Probiotic supplementation using Clostridium, Saccharomyces, and Lactobacillus species shows varying degrees of success.
Post-excretion Strategies: These focus on manure management after production, utilizing materials like sawdust and beneficial microbes including Lactobacillus plantarum and Enterococcus faecium to reduce emission severity (Konkol et al., 2022).
Comprehensive Ventilation Management
Ventilation serves as the cornerstone of effective air quality management in broiler houses, directly impacting both bird health and productive performance. A well-designed system ensures continuous fresh air supply, adequate oxygen delivery, and optimal temperature maintenance while remaining economically viable.
Modern broiler house ventilation typically employs three distinct strategies: minimal ventilation, transitional ventilation, and tunnel ventilation (Furlan et al., 2000).
Minimal Ventilation: The Foundation
Minimal ventilation focuses on maintaining basic air quality and temperature requirements during cooler periods and early production stages.
Indicators for Increasing Minimal Ventilation (Menegali et al., 2012):
– Air feels stuffy with high relative humidity
– Water droplets appear on incoming water lines
– Wall and ceiling condensation develops
– Litter becomes excessively wet
Indicators for Decreasing Minimal Ventilation (Mendes et al., 2013):
– Air quality approaches outdoor conditions (should remain warmer indoors)
– Litter becomes overly dry, creating dusty conditions
– House cannot maintain set-point temperature, particularly overnight
Bird Comfort Assessment:
– Proper Distribution: Birds should spread evenly throughout the facility. Empty patches may indicate cold air leaks, incorrect inlet settings, or non-functioning heaters.
– Cold Stress Signs: Birds huddling despite appropriate set-point temperatures may indicate sensor errors or inadequate temperature settings. Increase set-point by 0.5-1°C (Mujahid and Furuse, 2005).
– Heat Stress Indicators: Birds showing warmth stress at set-point temperatures may indicate sensor inaccuracy, excessive temperature settings, or high humidity effects. Verify air quality before temperature adjustments (Chowdhury et al., 2012).
Transitional Ventilation: The Bridge
Transitional ventilation bridges the gap between minimal and tunnel ventilation, activating when house temperatures exceed set-points but conditions don’t warrant full tunnel ventilation due to cold weather or young bird age.
The primary objective involves cooling the house through large volumes of fresh outside air to remove excess heat. This requires continuous fan operation with heaters deactivated. Air enters through sidewall inlets using negative pressure, directing airflow upward and away from birds. All sidewall and chimney fans, plus selected tunnel fans, facilitate proper airflow while tunnel inlets remain closed (Aviagen, 2019).
Monitoring and Adjustment (Akter et al., 2022):
– Bird behavior serves as the primary indicator of system effectiveness
– Cold bird signs: Huddling indicates discomfort; reduce air movement by deactivating fans and slightly increasing temperature
– Warm bird signs: Heat stress symptoms require additional fan activation and slight temperature reduction
– Transition timing: Switch to tunnel ventilation when birds remain uncomfortable despite maximum transitional ventilation
Tunnel Ventilation: Maximum Cooling
Tunnel ventilation provides the highest level of cooling capacity, implementing only after transitional ventilation proves insufficient for bird comfort.
This system creates powerful, high-speed airflow throughout the facility to generate significant wind-chill effects that make birds feel cooler. Success depends on air speed, temperature, humidity, bird age, and stocking density rather than simple temperature measurements. Management relies primarily on observing bird comfort and behavior, with 10-20% of birds showing light panting considered normal heat response (Lacy and Czarick, 1992).
System Requirements:
– Design Considerations: Maximum air speed determination based on ambient climate, bird numbers, weight, and stocking density
– Temperature Uniformity: House length temperature differential should not exceed 2.8°C (5°F) during maximum tunnel ventilation. Larger differences indicate air leaks, insufficient insulation, or inadequate fan capacity (Wheeler et al., 2003)
– Maintenance: Regular fan and cooling pad maintenance ensures optimal system performance
– Migration Control: Installing fences every 40 meters prevents birds from crowding at cooler house areas, maintaining uniform distribution and heat load
Conclusion: Integrated Air Quality Management
Harmful gas emissions in poultry houses represent a multifaceted challenge requiring comprehensive, integrated management approaches. Success depends on understanding the interconnected nature of air quality factors and implementing coordinated prevention and mitigation strategies.
The emission of harmful gases connects directly with other critical poultry management disciplines, including nutrition, housing design, environmental control, and bird welfare. Together, these elements create healthy production environments that support optimal productivity levels while protecting both animal and worker health.
Effective air quality management ultimately balances multiple competing priorities: maintaining bird comfort and performance, ensuring worker safety, minimizing environmental impact, and preserving economic viability. By understanding the complex relationships between oxygen requirements, harmful gas emissions, particulate matter control, and ventilation management, producers can create systems that optimize all these factors simultaneously.
The future of broiler production depends increasingly on sophisticated air quality management that integrates traditional management wisdom with advanced monitoring technologies and scientific understanding. This comprehensive approach ensures sustainable production systems that meet growing global protein demands while maintaining the highest standards of animal welfare and environmental responsibility.
References
Akter, S., Liu, Y., Cheng, B., Classen, J., Oviedo, E., Harris, D., & Wang-Li, L. (2022). Impacts of Air Velocity Treatments under Summer Conditions: Part II—Heavy Broiler’s Behavioral Response. Animals, 12(9), 1050.
Aviagen (2019), Essential ventilation management, available at: https://aviagen.com/assets/Tech_Center/Broiler_Breeder_Tech_Articles/English/AviagenEssentialVentilationManagement-2019-EN.pdf
Beker, A., Vanhooser, S. L., Swartzlander, J. H., & Teeter, R. G. (2003). Graded atmospheric oxygen level effects on performance and ascites incidence in broilers. Poultry science, 82(10), 1550-1553.
Burggren, W. W., Mueller, C. A., & Tazawa, H. (2015). Hypercapnic thresholds for embryonic acid–base metabolic compensation and hematological regulation during CO2 challenges in layer and broiler chicken strains. Respiratory Physiology & Neurobiology, 215, 1-12.
Carey, J. B., Lacey, R. E., & Mukhtar, S. (2004). A review of literature concerning odors, ammonia, and dust from broiler production facilities: 2. Flock and house management factors. Journal of Applied Poultry Research, 13(3), 509-513.
Chi, Q., Chi, X., Hu, X., Wang, S., Zhang, H., & Li, S. (2018). The effects of atmospheric hydrogen sulfide on peripheral blood lymphocytes of chickens: perspectives on inflammation, oxidative stress and energy metabolism. Environmental research, 167, 1-6.
Chowdhury, V. S., Tomonaga, S., Nishimura, S., Tabata, S., & Furuse, M. (2012). Physiological and behavioral responses of young chicks to high ambient temperature. The Journal of Poultry Science, 49(3), 212-218.
Furlan, R. L., Macari, M., Secato, E. R., Guerreiro, J. R., & Malheiros, E. B. (2000). Air velocity and exposure time to ventilation affect body surface and rectal temperature of broiler chickens. Journal of Applied Poultry Research, 9(1), 1-5.
Klentz, R. D., & Fedde, M. R. (1978). Hydrogen sulfide: effects on avian respiratory control and intrapulmonary CO2 receptors. Respiration physiology, 32(3), 355-367.
Konkol, D., Popiela, E., Skrzypczak, D., Izydorczyk, G., Mikula, K., Moustakas, K., … & Chojnacka, K. (2022). Recent innovations in various methods of harmful gases conversion and its mechanism in poultry farms. Environmental Research, 214, 113825.
Lacy, M. P., & Czarick, M. (1992). Tunnel-ventilated broiler houses: broiler performance and operating costs. Journal of Applied Poultry Research, 1(1), 104-109.
Liu, X., Zhang, Y., Yan, P., Jing, Q., Wei, X., Liu, R., … & Wu, B. (2015). Effects of different padding on air quality in broiler house and growth physiological index of broilers. Agricultural Science & Technology, 16(12), 2764.
Mendes, A. S., Moura, D. J., Nääs, I. A., Morello, G. M., Carvalho, T. M. R., Refatti, R., & Paixao, S. J. (2013). Minimum ventilation systems and their effects on the initial stage of turkey production. Brazilian Journal of Poultry Science, 15, 7-13.
Menegali, I., Tinôco, I. F., Zolnier, S., Carvalho, C. D., & Guimarães, M. C. D. C. (2012). Influence of different systems of minimum ventilation on air quality in broiler houses. Engenharia Agrícola, 32, 1024-1033.
Mujahid, A., & Furuse, M. (2009). Behavioral responses of neonatal chicks exposed to low environmental temperature. Poultry science, 88(5), 917-922.
Patterson, P. H. (2005). Management strategies to reduce air emissions: Emphasis—Dust and ammonia. Journal of Applied Poultry Research, 14(3), 638-650.
Reece, F. N., & Lott, B. D. (1980). Effect of carbon dioxide on broiler chicken performance. Poultry science, 59(11), 2400-2402.
Saksrithai, K., & King, A. J. (2018). Controlling hydrogen sulfide emissions during poultry productions. J Anim Res Nutr, 3(1), 2.
Swelum, A. A., El-Saadony, M. T., Abd El-Hack, M. E., Ghanima, M. M. A., Shukry, M., Alhotan, R. A., … & El-Tarabily, K. A. (2021). Ammonia emissions in poultry houses and microbial nitrification as a promising reduction strategy. Science of The Total Environment, 781, 146978.
Wang, K., Shen, D., Dai, P., & Li, C. (2023). Particulate matter in poultry house on poultry respiratory disease: a systematic review. Poultry Science, 102(4), 102556.
Wheeler, E. F., Zajaczkowski, J. L., & Sabeh, N. C. (2003). Field evaluation of temperature and velocity uniformity in tunnel and conventional ventilation broiler houses. Applied Engineering in Agriculture, 19(3), 367.
Wicklin, G.; Czarick, M. Particulate Emissions from Poultry Housing. In Proceedings of the ASAE Annual International Meeting,Minneapolis Convention Center, Minneapolis, MN, USA, 10–14 August 1997; pp. 10–14.
Winkel, A., Mosquera, J., Aarnink, A. J., Koerkamp, P. W. G., & Ogink, N. W. (2016). Evaluation of oil spraying systems and air ionisation systems for abatement of particulate matter emission in commercial poultry houses. Biosystems Engineering, 150, 104-122.
