What do layer farms look like?
In the United States, the top five states for egg production are: Iowa, Ohio, Indiana, Pennsylvania, and Texas*. Seventy-five percent of all egg laying hens are housed at farms that have more than 100,000 laying chickens on-site.** Recommended: Common poultry terms and definitions.
Most layer farms house birds inside buildings and use fans to maintain the preferred temperature and provide sufficient fresh airflow. These farms have strict visitation rules to minimize the transfer of disease into the farms. As a result, visitors are limited and there are strict clothing and sanitation protocols for those who need access (workers, veterinarians, feed delivery, manure applicators, etc.). Following these biosecurity rules reduces the risk for disease.
In the pictures below, you will see several layer hen farms. Photo 1 shows a house with a paved area under the cages for the purpose of scraping and removing the manure every 3 days. Photo 2 is a high-rise house or multi-level building with the hens occupying the upper level and a manure collection or storage area in the bottom level. Photo 3 is a building with a manure belt and cage system (more on that later). Photo 4 shows a new set of cage-free buildings (photo taken in 2013). The rate of construction of cage-free systems has increased in response to consumer demands. As you can see, it is not easy to tell from the outside what type of production system is used inside the barns.
*Data source: 2015 Chicken and Eggs Summary and ** USDA Census of Agriculture
What about the inside?
Since the 1960s, layer hens have been housed largely indoors and in cages. The predominant design, called a high-rise house, arranged cages in a manner that directed manure through a slot in the floor and into a storage area or manure pit in the lower level. Early designs utilized an A-frame arrangement. Newly-built houses are no longer of this type, but many of these buildings are still in use. Photo 1 below shows a row of cages in a more contemporary high-rise house.
Henhouse designs continue to evolve and most of the new buildings constructed in the past decade use manure belt systems (Photos 2 and 3 below) that handle and store manure differently than in the high-rise system (more on that below). Today, hens housed in manure belt systems account for about 50% of all U.S. egg production. Manure belts can be used with conventional cages, each containing around 8 birds and stacked one on top of another or with enriched colony enclosure cages (more below). The belt below each cage catches manure to prevent it from dropping on the birds below and then carries the manure away for storage outside of the hen house.
Enriched colony systems (see cover photo) use large enclosures that contain around 60 birds and provide more space for each bird than in conventional cage systems. In cage-free systems (Photo 4 above) the birds can freely move throughout the barn. Fewer birds will fit into a cage-free building compared to conventional cages or enriched colony housing. Cage free systems are gaining popularity in the U.S. but at the present time (2016) hens housed in these systems account for less than 10% of U.S. egg production. As farms look to replace or remodel barns, industry experts expect enriched colony and cage-free systems to become more common.
A common characteristic of all these systems is that hens are kept under a roof and in a building to ease their care, handling, feeding, egg collection, and manure handling and removal. If the farm also stores manure in a covered structure, rain, snowmelt, and stormwater never come into contact with the manure.
The video below describes different housing systems and shows some diagrams and photos of battery cage, enriched colony, and cage-free systems. It also introduces manure management practices. The video is an excerpt of a webcast presentation by Dr. Hongwei Xin from Iowa State University.
What about the manure?
Estimates of manure production vary, but a barn with 100,000 hens produces around 1,500 tons of manure every year.
Manure from layer housing is predominantly handled as a solid or semi-solid that is moist when excreted and then dries out, to varying degrees, during the manure movement and storage process. High-rise systems have two sections-the upper level where the hens are housed and fed and where they lay their eggs, and the dry, ground floor section below (Photo 1, below). The manure pit extends the entire length of the building and serves as long-term storage. Airflow in the building is designed to dry the manure and direct odors out through fans. Ventilation is important in these systems for several reasons, including the fact that it dries the manure, reducing the amount of ammonia produced and released. This improves air quality in the building and increases the nutrient value of the manure. The manure is generally removed once a year to be spread on crop fields, although some farms compost the manure and remove it more often.
The building in Photo 3 below contains a paved alley and the manure is removed every three days. On this farm, the manure is moved to a composting area, but most farms move the manure to long term storage, which might be uncovered (Photo 4 below) or covered (recommended, Photo 5 below).
As noted above, all new construction, including some cage-free systems, now use belts (Photo 2 below) to convey manure out of the building to a separate storage structure (Photo 5 below). As older buildings are remodeled, many are being converted to manure belt systems. Airflow in the building is set up to help dry the manure on the belts and manure is removed often, with 1-3 days being a common interval.
Less common housing systems for layer farms use flush or scrape systems to collect manure as a slurry or liquid. This is an older system and only about 5% of U.S. eggs are produced in this type of housing today. The manure from these systems is stored in a separate earthen, steel, or concrete structure outside of the housing facility. Many of these storage structures are managed as anaerobic lagoons to treat the waste. Liquid from the storage is sometimes recycled into the building to flush or clean accumulated manure and move it to the storage.
Any large livestock or poultry operation with more than a threshold number of animals at a location is subject to the manure management requirements of the Clean Water Act and specifically the Concentrated Animal Feeding Operation (CAFO) Rule. This federal rule, usually enforced by the state under federal authority, requires that rainwater or stormwater that comes into contact with animals, manure or feed be contained and managed to prevent discharges to surface water. In the case of layer farms, these federal requirements apply to farms with 82,000 or more hens if the manure is handled in a dry form. Most large farms are required to have a permanent structure or area for storing solid manure after it is removed from the layer houses (see Photos 4 and 5). Rules regarding the location, size, and other aspects of the storage can vary from state to state. Some states require the manure storage to be covered or on an impervious (concrete or lined) pad.
Most manure is applied to fields to fertilize crops or pastures (Photo 1 below). The vast majority of layer manure today is sold to third parties for this purpose although some egg producers still apply their manure to their own crop land. In all cases, a large layer operation is required to comply with the federal CAFO rule requirements. Chicken manure is rich in nutrients like nitrogen, phosphorus, and potassium, all of which are needed for plant growth. Solid manure is removed from the storage area and loaded into trucks or manure spreaders for application to the land applications sites. Depending on distance and accessibility to the field, manure may be hauled on public roads. Care is needed to prevent excessive dust and spillage during loading and hauling.
Find out more about manure and nutrient management.
Ideally, manure is moved directly from the storage and applied right away to the field. This is not always feasible so another choice is to stockpile manure or temporarily store it in the field where it will be used (Photo 2 below). Again, typically, there are rules that govern whether or not a pile needs to be covered, how far away from water it can be, and how long it can be there. These rules vary by location.
Large layer operations often also include egg wash facilities (Photo 1 below). The eggs are removed from the houses and washed in a separate building. Automatic washers remove manure and other debris from the shells. The resulting liquid waste stream contains cleaning compounds and small amounts of manure, broken eggs, and other organic materials. This wastewater is piped or pumped to large tanks or holding ponds for storage (Photo 2 below). The wastewater can be pumped or trucked to fields for crop irrigation.
Are there other ways to handle manure?
Are there new or emerging technologies that may be common one day? It is hard to know which will be common, but there are some innovative manure management technologies being used by a few layer farms.
One of the most recent and practical innovations has been made possible by the advent of manure belt systems in egg production. Manure on the belts dries out relatively quickly, which halts biological activity and therefore ammonia production and volatilization. Biological activity and ammonia loss is further reduced due to the manner in which belt-conveyed manure is stored-separately from the animal house. The surface area of the manure piles is greatly reduced compared to high-rise systems, decreasing manure contact with oxygen. The separate storage area improves air quality for the hens and the workers who care for them. The end result of this (ongoing) innovation is a stable manure that is lighter to handle and transport, and higher in crop nutrient value.
Pelletization of dried manure further stabilizes the material, reducing dust and allowing it to be handled like a commercial fertilizer product. Dry pellets flow better in transfer, transport, and application equipment. Pelletization can also increase the acceptability of the product as an organic fertilizer for residential or recreational (golf course) uses. The use of pelletization at layer farms is growing.
Many operations are finding the investment in supplemental drying (Photo 1 below) and pelletization to be economical given the growing recognition of the value of manure in increasing soil organic matter and increasing beneficial biological activity. Pelletized manure is an alternative source of nitrogen during times of high commercial fertilizer prices as well.
Black soldier fly (BSF) larvae are shown in Photo 2 below. This is an alternative system that has promise, but requires additional research, development, and demonstration before use in commercial operations of any size. Black soldier flies are not pests the way we think of house flies or stable flies. They were first noticed on accumulated manure several decades ago when open-sided layer houses were common. Current research and development efforts with BSF focus on raising the larvae on animal manure, reducing the volume of the manure and its nutrient content. The BSF larvae retain many of the nutrients originally present in the manure and the larvae have been shown in research to be a good source of nutrition in animal feed. The nutrients in the manure get recycled into the animals through the larvae as a direct feed source and not into the grain that might otherwise have been fertilized with manure. BSF larvae are not currently (2016) approved for commercial sales but a farm may be able to produce larvae for its own use. At this time, recycling nutrients with BSF larvae is mostly used by small-scale farms but research continues to explore its applications to large, commercial operations.
Learn more about manure treatment technology.