Broiler chickens are typically raised in large, fully enclosed sheds constructed of metal and/or wood. Most facilities are dimly lit to discourage birds’ activities, optimize their feed conversion, and save on energy costs.[1] A typical broiler shed measures 43’x 500’ and houses ~30,000 birds.[2]
Floors consist of concrete or compacted soil covered by litter, which can be made from a variety of materials including wood shavings, sawdust, rice or peanut hulls, sand, or processed paper. The materials absorb urine, feces, feathers, dander, and spilled feed and water.[3]
The litter is typically left in place from flock to flock. Some broiler operations do a total cleanout once a year, though the practice of reusing litter for two or even more years “has become a standard in the industry.”[4] This is due to the cost of fresh material, the labor involved with removal, and the growing environmental concerns regarding water and soil pollution from cropland application.[5,6]
Densely packed birds spend their lives in physical contact with this noxious and contaminated material, either standing or lying on it. This is the source of many common injuries and diseases.
Olanrewaju, H.A. et al., (2016). Effects of light sources and intensity on broilers grown to heavy weights. Part 1: Growth performance, carcass characteristics, and welfare indices. Poultry Science, 95(4), 727–735, pp. 727, 734. [Low lighting encourages inactivity leading to more efficient weight gain.]
See, Poultry Factory Farm Sizes
Ritz, C.W. et al., (2017) Litter Quality and Broiler Performance, UGA Extension Bulletin 1267. https://secure.caes.uga.edu/extension/publications/files/pdf/B%201267_5.PDF
Ritz, C.W. et al., (2017), p. 3.
Hubbard, L.E. et al., (2020). Poultry litter as potential source of pathogens and other contaminants in groundwater and surface water proximal to large-scale confined poultry feeding operations. The Science of the Total Environment, 735, 13945, p. 13. [“The converging lines of evidence point to the spreading of the poultry litter on land adjacent to the poultry CPFOs (concentrated poultry feeding operations) as a source of microbial and chemical contaminants to groundwater and surface water.”]
Ashworth, A.J. et al., (2019). Nutrient Characteristics of Poultry Manure and Litter. In Animal manure: Production, characteristics, environmental concerns, and management (Waldrip et al. eds.) ASA Special Publication 67, Madison, WI, pp. 79–81.
Ammonia is the most abundant toxic gas present in poultry houses.[1] It is found at particularly high levels in houses where stocking density is high, litter is used for prolonged periods, and moisture levels and temperatures are high. Generally, over half of the nitrogen excreted by broiler chickens is lost into the air as ammonia before the litter is removed from houses.[2] The 24/7 exposure to elevated levels of ammonia is harmful to poultry health, irritating eyes and damaging to respiratory function.[3,4] Human workers can protect themselves with fitted dust masks and respirators, but the birds have no such protection.
National Chicken Council Broiler Welfare Guidelines recommend a maximum ammonia concentration in poultry houses of 25 ppm.[5] However, it has been found that “Ammonia concentration in a commercial broiler house commonly exceeds 50 ppm.”[6]
Also harmful to poultry health is airborne particulate matter consisting primarily of manure, feed, feathers, dander, litter, and biological contaminants including bacteria, viruses, and mold. “Airborne dust levels in some poultry barns can occasionally be high enough to produce a visible haze, making it difficult to see from one end of the building to the other in very long barns.”[7] Common effects on the birds include impairments and diseases of the eyes and lungs.[8]
Naseem, & King, A. J. (2018). Ammonia production in poultry houses can affect health of humans, birds, and the environment—techniques for its reduction during poultry production. Environmental Science and Pollution Research International, 25(16), 15269–15293, p. 15273.
Miles, D. M. (2012). Poultry litter moisture management to reduce ammonia. USDA Agricultural Research Service, p. 1.
https://www.ars.usda.gov/ARSUserFiles/np212/LivestockGRACEnet/LitterMoisture.pdfMiles, D. M. et al., (2004). Atmospheric ammonia Is detrimental to the performance of modern commercial broilers. Poultry Science, 83(10), 1650–1654, p. 1650.
Bist, R. B. et al., (2023). Ammonia emissions, impacts, and mitigation strategies for poultry production: A critical review. Journal of Environmental Management, 328, 116919, p. 2.
National Chicken Council (December 2022) National Chicken Council Broiler Welfare Guidelines and Audit Checklist, p. 11. https://www.nationalchickencouncil.org/wp-content/uploads/2023/01/NCC-Broiler-Welfare-Guidelines_Final_Dec2022-1.pdf
Miles, D. M. et al. (2004), p. 1650.
Penn State Extension (2020) Poultry Dust – What You Need to Know About Impact on Bird Health. https://extension.psu.edu/poultry-dust-what-you-need-to-know-about-impact-on-bird-health
Bist, & Chai, L. (2022). Advanced Strategies for Mitigating Particulate Matter Generations in Poultry Houses. Applied Sciences, 12(22), 11323, Table 6.
The National Chicken Council makes the following recommendations to its members (which according to NCC account for ~95% of the chickens produced in the U.S.). These recommendations are based on target market weights.[1]
National Chicken Council (December 2022) National Chicken Council Broiler Welfare Guidelines and Audit Checklist, pp. 12-13.
The majority of factory farmed hens are confined in small wire cages. First raised as caged pullets in grow-out buildings, at about 4 months of age they are moved to their final cage in a laying house where they will stay for the remainder of their productive life. Large houses contain 50,000 to 350,000 laying hens.[1,2]
The rows of wire mesh cages (termed battery cages) are stacked in tiers, mostly 4-tier, though as many as 8-tier in high-rise houses. These cage systems are usually “stair-stepped” to allow droppings to fall into a basement or pit without passing through cages in the lower tiers. Manure forms cones beneath each row of cages, and manure removal may occur only once per year.[3,4] The hens spend their lives tightly confined with other birds in this barren, noxious environment either standing or sitting on wire mesh.
It is clear to almost anyone aware of these conditions that, even by the standards of the animal ag industry, this is unusually cruel treatment. The European Union banned battery cages for hens as of 2012.[5]
USDA, APHIS (2013) Poultry Industry Manual, Foreign Animal Disease Preparedness & Response Plan (FADPRep), pp. 102-103.
See also, Poultry Factory Farm Sizes
USDA, APHIS (2013) Poultry Industry Manual, p. 106.
Ashworth, A. J. et al., (2019). Nutrient Characteristics of Poultry Manure and Litter. In Animal manure: Production, characteristics, environmental concerns, and management (Waldrip et al. eds.) ASA Special Publication 67, Madison, WI, p. 73.
James Andrews (January 19, 2012) European Union Bans Battery Cages for Egg-laying Hens, Food Safety News. https://www.foodsafetynews.com/2012/01/european-union-bans-battery-cages-for-egg-laying-hens/
The USDA and the United Egg Producers (UEP) have recommended maximum ammonia concentrations of 25ppm; the UEP notes that ideal levels are under 10ppm.[1,2] However, a recent review of studies on ammonia in poultry houses reports that ammonia concentrations in layer houses often exceed 25ppm, and sometimes average close to 50ppm.[3] High levels of ammonia have injurious effects on bird health, as noted in the previous air-quality question about broiler chickens.
Dana Miles (2012) Poultry Litter Moisture Management to Reduce Ammonia, USDA Agricultural Research Service.
United Egg Producers (2017) Animal Husbandry Guidelines for U.S. Egg-Laying Flocks, Guidelines for Cage Housing, p. 24. [“The ammonia concentration to which birds are exposed should ideally be less than 10 ppm and should rarely exceed 25 ppm.”]
Bist, R. B. et al., (2023). Ammonia emissions, impacts, and mitigation strategies for poultry production: A critical review. Journal of Environmental Management, 328, 116919, Table 2.
The United Egg Producers (UEP) recommends 67 to 86 sq. inches per bird.[1] The UEP reports that more than 90% of all U.S. egg production is produced under UEP guidelines.[2]
At the minimum recommendation of 67 sq. inches, the total space allotment per hen is 8.2 by 8.2 inches. That space allotment almost exactly equals the footprint of a standard Apple iPad. A typical commercially raised egg-laying hen would require about four times that area to flap her wings.[3]
A standard size layer cage is 24” wide x 25.125” deep, with a floor area of 603 sq. inches.[4,5] Housing nine birds in this size of cage follows the UEP minimum guidelines of 67 sq. inches per bird.
The UEP makes no specific recommendations on the height of cages other than “hens should be able to stand comfortably upright in their cage.”[6] Unsurprisingly, hens show “a strong preference for cages which have a large vertical space allowance.”[7]
The construction of wire cages can be complex, including sloped floors and varying heights within a single cage or differences in width and depth measurements. Additionally, cage construction and sizes typically vary within facilities, with configurations on lower levels differing from higher ones. This makes it difficult for producers to know if they are meeting UEP guidelines.[8]
The typical number of egg-laying hens on a factory farm is 1.2 million. Large commercial sheds usually contain between 50,000 and 350,000 birds.
United Egg Producers (2017) Animal Husbandry Guidelines for U.S. Egg-Laying Flocks 2017 Edition, Guidelines for Cage Housing, p. 19. [“Space allowance should be in the range of 67 to 86 square inches of usable space per bird to optimize hen welfare.”]
United Egg Producers (n.d.) About UEP Certified. https://unitedegg.com/programs/uep-certified/
Mench, J. A. & Blatchford, R. A. (2014). Determination of space use by laying hens using kinematic analysis. Poultry Science, 93(4), 794–798, p. 794.
FDI Cage System (2018) Standard Layer Cages, Standard Cage Dimensions, https://www.fdipoultryequipment.com/wp-content/uploads/2018/10/Standard-layer-information-pamphlet.pdf
The Big Dutchman UniVENT Layer Cage System, p. 4. https://www.bigdutchmanusa.com/en/egg-production/products/housing-systems/conventional-cage-systems/univent-layer/
United Egg Producers (2017) Animal Husbandry Guidelines for U.S. Egg-Laying Flocks 2017 Edition, p. 19.
Dawkins, M. S. (1985). Cage height preference and use in battery-kept hens. The Veterinary Record, 116(13), 345-347.
Kiess, A. S. et al., (2012). A standardized cage measurement system: A versatile tool for calculating usable cage space. Journal of Applied Poultry Research, 21(3), 657–668, p. 657. [“Because there is neither a quantitative value given for cage height nor an established method for calculating usable space, meeting this (UEP) guideline poses challenges for producers.”]
Hens living in cage-free housing are raised exclusively indoors in dimly-lit, large sheds that typically house 50,000 to 350,000 birds.
The USDA requires the following treatment for hens that lay eggs labeled as cage-free: The hens are “able to roam vertically and horizontally in indoor houses, and have access to fresh food and water. Cage-free systems vary from farm-to-farm, and can include multi-tier aviaries. They must allow hens to exhibit natural behaviors and include enrichments such as scratch areas, perches and nests. Hens must have access to litter, protection from predators and be able to move in a barn in a manner that promotes bird welfare.”[1]
Most houses are the “multi-tier aviaries” to which the USDA refers, while some are single-level, all-litter floor. The United Egg Producer guidelines make clear that cage-free housing must have 6 linear inches of perching space per bird and 9 sq. ft. of nesting area per 100 birds.[2]
While cage-free housing allows hens to perform some (arguably highly constrained) natural behaviors such as foraging, dustbathing, and wing-flapping, because of these activities on the litter floor where manure accumulates, the levels of ammonia, particulate matter, and airborne bacteria all tend to be higher than in caged systems.[3,4]
In a 2023 report from the European Food Safety Authority, a large group of scientists analyzed the welfare of laying hens in a variety of cage-free systems. The report identified a wide range of health problems, including bone and soft tissue lesions, problems getting rest, restriction of movement, skin disorders, and inability to perform exploratory or foraging behaviors.[5] Despite the immense welfare problems, most analyses note a large improvement compared to hens in cages. For additional reviews of the relative advantages and disadvantages of cage-free systems with regard to animal welfare, see the following sources.[6-9]
USDA Agricultural Marketing Service (2016) Shell Egg Labeling guidelines for product bearing the USDA grademark, p. 5. [The small percent of eggs labeled “free-range” must come from hens that have “continuous access to outdoors during their laying cycle.”]
United Egg Producers (2024) 2024 Cage-Free Housing: Animal Welfare Guidelines for U.S. Egg-Laying Flocks, pp. 10-25. [The UEP reports that more than 90% of all U.S. egg production is produced under UEP guidelines.]
Chai, L. et al., (2018). Mitigating ammonia and PM generation of cage-free henhouse litter with solid additive and liquid spray. Transactions of the ASABE, 61(1), 287-294, p. 288. [“The high NH3 levels of CF houses primarily arise from the extended accumulation of manure on the litter floor, whereas the high PM levels primarily arise from dustbathing and foraging activities of the birds on the litter.”]
Chai, L. et al., (2018). Mitigating airborne bacteria generations from cage-free layer litter by spraying acidic electrolysed water. Biosystems Engineering, 170, 61–71, p. 62.
EFSA Panel on Animal Health and Animal Welfare (2023), Nielsen, S.S. et al., Scientific Opinion on the welfare of laying hens on farm. EFSA Journal 2023;21 (2):7789. https://doi.org/10.2903/j.efsa.2023.7789
Hartcher, & Jones, B. (2017). The welfare of layer hens in cage and cage-free housing systems. World’s Poultry Science Journal, 73(4), 767–782.
Hannah Ritchie (2023) Do better cages or cage-free environments really improve the lives of hens? Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/do-better-cages-or-cage-free-environments-really-improve-the-lives-of-hens’ [Online Resource]
Quantifying Pain in Laying Hens. (2021) Schuck-Paim C., Alonso W.J. (eds.) Independently published. published. https://tinyurl.com/bookhens
National Farm Animal Care Council (Canada) (2013). Code of Practice for the Care and Handling of Pullets, Layers, and Spent Fowl: Review of Scientific Research on Priority Issues.
According to United Egg Producers (UEP) guidelines, at placement hens should be given the following minimum amounts of usable floor space:
1.0 square foot per hen in multi-tier housing or slatted floor housing. 1.5 square feet per hen in single-level all litter floor housing.
Explaining the space differentials, UEP notes that “Because multi-tiered aviaries and partially slatted systems provide hens with access to vertical space within their barn, they effectively have more space to move around than hens in all-litter floor systems.”[1] However, as it’s defined, usable floor space incorporates more than just space on the ground. “Usable floor space includes the combined litter [ground level] and drop-through area including elevated tiers, and covers over belts, but excludes perch and nest space…”[2,3]
United Egg Producers (2024) 2024 Cage-Free Housing: Animal Welfare Guidelines for U.S. Egg-Laying Flocks, p. 21. [The UEP reports that more than 90% of all U.S. egg production is produced under UEP guidelines.]
United Egg Producers (2024) 2024 Cage-Free Housing. [For perches, UEP guidelines recommend a minimum of 6 in. of linear perch space per hen, so all hens can perch simultaneously. (at p. 21) Nesting space is also recommended at a minimum of 9 sq. ft. per 100 hens, or 3.6 by 3.6 inches per hen. (at pp. 23-25)]
United Egg Producers Housing Diagrams (2021)
https://uepcertified.com/wp-content/uploads/2021/08/Hen-Housing-Diagrams.pdf
About 40% of egg-laying hens are raised in cage-free systems.[1]
The percentage of cage-free egg-laying hens is steadily increasing as consumer and retailer demand for cage-free eggs grows. This is mostly due to the animal advocacy movement’s work in support of state referendums and efforts to secure food corporation commitments.[2-4]
USDA Agricultural Marketing Service (August 30, 2024) Monthly USDA Cage-Free Shell Egg Report. [All cage-free layers = 123,561,359 as of August]; USDA NASS Chickens and Eggs (August 23, 2024) ISSN: 1948-9064, p. 7. [all egg-type layers = 304,416,000 as of July]
Danielle J. Ufer, USDA Economic Research Service (2022) State Policies for Farm Animal Welfare in Production Practices of U.S. Livestock and Poultry Industries: An Overview, Economic Information Bulletin No. 245, p. report summary. [“State policies addressing animal welfare passed by a popular vote as a ballot initiative or by State legislative bodies. Twenty-three States allow initiatives that could feasibly pass farm animal welfare legislation. Of these, 12 States passed laws by ballot or by other means that cover farm animal welfare before slaughter.” p. 3.]
Compassion in World Farming, Egg Track 2022 Report. https://www.ciwf.org.uk/media/7452386/eggtrack-2022-report.pdf [working with food companies to transition to cage-free egg supply and ensure compliance]
Bollard, L., (2019). Will Companies Make Good on Cage-Free Pledges. Open Philanthropy, San Francisco, USA. https://www.openphilanthropy.org/research/will-companies-make-good-on-cage-free-pledges/
In the U.S., turkeys are typically raised in 2 stages. Brooding is the rearing of chicks in separate housing until 5 or 6 weeks of age. From there they are moved to finishing or grow-out houses until they reach market weight. Hens and toms (male turkeys) are raised separately.[1]
Grow-out houses are usually 40-50 ft. wide and 500-700 ft. long or 20,000 to 35,000 square feet. The housing is closed, heavily insulated, dimly lit, and ventilated with automated fans.[2,3] Turkeys are raised on a single-level hard floor covered with litter, usually made from wood shavings, sawdust, rice hulls, or straw.[4,5]
We don’t have much recent information about typical air emissions in turkey housing. In 2005, the EPA and the animal ag industry entered into an agreement to monitor air emissions from various animal ag industries. However, as noted by the EPA’s Office of Inspector General in 2017, not enough turkey AFO operators signed up to participate in the monitoring effort. The EPA has a long history of delay regarding efforts to develop air emission guidelines for AFOs.[6]
USDA, APHIS (2013) Poultry Industry Manual, Foreign Animal Disease Preparedness & Response Plan (FADPReP), pp. 60-67.
USDA, APHIS (2013) Poultry Industry Manual, p. 53.
Marchewka, J. et al., (2013). Review of the social and environmental factors affecting the behavior and welfare of turkeys (Meleagris gallopavo). Poultry Science, 92(6), 1467–1473, p. 1470. [“Although low lighting intensity (1/10 lx) is used to reduce the risk of undesirable behaviors such as feather pecking and cannibalism, it can also inhibit walking, foraging, exploration, and social behaviors.”]
Chepete, H. J. et al., (2010). Effect of Partially Covering Turkey Litter Surface on Ammonia Emission. Iowa State University Digital Repository, p. 513.
USDA, APHIS (2013) Poultry Industry Manual, p. 60.
U.S. EPA Office of Inspector General (2017) Eleven Years After Agreement, EPA Has Not Developed Reliable Emission Estimation Methods to Determine Whether Animal Feeding Operations Comply With Clean Air Act and Other Statutes, p. 4, fn 11.
It’s difficult to ascertain typical space allotments for factory farmed turkeys in the U.S., and there isn’t much industry guidance available.
The National Turkey Federation (NTF), which claims to represent more than 95% of the turkey industry, does not make specific recommendations regarding space allocation guidelines. It recommends only that turkeys should be able to walk through the growing area, stand up, sit down, and spread their wings.[1]
In 2012, the NTF explained that definitive space recommendations were “not necessarily feasible,” but allowed that 15 lbs. per sq. ft. “could be used as a measurable standard.”[2] Based on average slaughter weight, this would give slightly over 1 sq. ft. of space to the average turkey hen weighing 15.5 lbs. (or 12.2″ x 12.2″). It would give about 2.5 sq. ft. to an average tom weighing 38 lbs. (or 19.1″ x 19.1″).[3] Hens and toms are raised in separate buildings.
The USDA has reported that in a typical grow-out house, hens receive “at least” 2 sq. ft of floor space, and toms 3 sq. ft. of floor space, though they present no data in support of these figures.[4]
Predictably, a 2017 literature review found that higher stocking densities generally lead to higher mortality rates, along with increased foot and respiratory problems. And “while industry standards and guidelines focus on providing turkeys with adequate space to perform particular behaviors, there is currently no scientific information available as to the amount of space turkeys need for particular behaviors.”[5]
National Turkey Federation (2024) NFT Commercial Turkey Audit Worksheet, On Farm Best Management Practices, see item #6.4 Space Allowance. https://www.eatturkey.org/animal-welfare/standards/
National Turkey Federation (2012) Animal Care Best Management Practices, p. 46.
National Turkey Federation (2024) Raising America’s Turkeys, https://www.eatturkey.org/raising-turkeys/ [“A hen usually takes 14 weeks and weighs 15.5 pounds when processed, but a tom takes roughly 18 weeks to reach a market weight of 38 pounds.” Note: as a comparison, a Border Collie generally weighs between 30-40 lbs.]
USDA, APHIS (2013) Poultry Industry Manual, Foreign Animal Disease Preparedness & Response Plan (FADPRep), p. 63.
Erasmus, M. A. (2017). A review of the effects of stocking density on turkey behavior, welfare, and productivity. Poultry Science, 96(8), 2540–2545, p. 2544. [“In general, higher densities (greater than 29.3 kg/m2 or 6 lb/ft2) are associated with reduced body weight, reduced feed efficiency, and increased mortality rates. Moreover, higher stocking densities lead to increased risks of footpad dermatitis, breast blisters, and respiratory problems.”]