What do pig farms look like?
In the 1950s it was common to see pigs outdoors in earthen lots. In the 60s, confinement buildings with slatted concrete floors came into prominence in the U.S. The industry we see today largely developed in the 1980s and 90s as farms became much larger and the industry became more vertically integrated. Three states currently (2016) account for more than 50% of pig production-Iowa, North Carolina, and Minnesota. Only 13% of pig farms sell more than 5,000 pigs per year, but those farms account for more than 91% of the pigs sold (source: U.S. Department of Agriculture [USDA] Census of Agriculture). Recommended: Common pig terms and definitions.
Most pig farms have several barns, but some have a single barn on a site. Most barns use a combination of natural ventilation (controlled by raising and lowering curtains) and mechanical ventilation (fans). Photos 1-5 below (hover your cursor over a photo to see the caption) show several different farms.
What about the inside?
Inside pig barns, the concrete floors have slats with narrow open spaces in between (Photo 1, below). As pigs move around the manure is pushed down through the openings. Pigs are grouped into pens (Photos 2 and 3, below) with a feeder and water source in each pen. An aisle down the center of the building allows access for workers to inspect pigs and take care of repairs and maintenance.
Pig barns are designed for specific stages of the pig's life cycle. The different types of operations include:
- Boar studs, where male pigs are kept for breeding purposes.
- Farrowing barns, where baby pigs are born and live until weaning.
- Nursery barns, where piglets are raised from weaning until the grow/finish phase.
- Grow-finish barns, where pigs are raised from around 50 pounds until they are marketed at around 260 pounds.
This tour focuses on grow-finish pigs.
How do pig farms handle manure?
The amount of manure produced by pigs varies greatly based on animal size, the building temperature, feed ration, and other factors. As a rough estimate, 600 pigs in a barn produce approximately 1,000 gallons of manure every day. This does not include wasted feed, spilled water, wash water, or liquid added to the manure collection and storage.
Most manure on pig farms is handled as a liquid or slurry. Deep pit pig barns are built over a deep concrete pit designed for long term manure storage (Photo 1, below). The manure from the pigs falls through the openings between the concrete slats and drops directly into the pit. Once or twice each year this slurry manure is mixed thoroughly (agitated) and pumped into a tanker for transport and application to crop fields. Good ventilation of the pits (fans) is essential to prevent the buildup of gases that can lead to explosions (methane) or injury or death to pigs and humans (hydrogen sulfide). Deep pit systems are the preferred option for new buildings for grow/finish pigs (young pigs raised to sell for meat).
Flushing systems for collecting manure use recycled liquid from the top layer of the manure storage tank to flush the manure out of the building into the outdoor manure storage. This type of barn includes a shallow flush gutter under the slatted flooring instead of a deep storage pit. Flushing is usually done several times per day. Some farms use fresh water to flush manure as a way to reduce odors. While not yet common, there is research into using mechanical scrapers instead of flushing.
Some pig farms collect manure with a system that works a little like a combination of pits and flushing systems. In a pull-plug or pit recharge system, manure is stored in a shallow pit below the barn for 4-7 days (pit recharge) or 1-2 weeks (pull-plug). When pits are emptied, the manure drains to the outdoor storage. Pit recharge systems partially refill the pit with water. By alternating which pits are emptied and when, the farmer can manage the odors inside the buildings and in the outdoor storage. Photos 2, 3, and 4 below show outdoor liquid manure storage-these are what manure storage looks like in pull-plug, pit recharge, and flush systems.
Photos 5 and 6 above show examples of land application of pig manure. The manure in Photo 5 is being injected below the surface of the soil. This is usually preferred because of reduced odors and nutrient conservation (less ammonia nitrogen is lost to the air). Photo 6 shows a system where the tractor drags a long hose across the field. Manure is pumped through the hose to the applicator. In this example, the manure is being applied to the soil surface.
Are there other ways to handle manure?
All the systems described so far collect and handle manure as a slurry or liquid. Manure from these systems is often land applied directly from the storage structure. However, slurry manure collected from these common pig housing systems is also suitable for anaerobic digestion. The U.S. currently has almost 250 digesters on livestock farms. Digesters completely enclose the manure to exclude oxygen and encourage methane-producing bacteria to be active. The resulting biogas can be used to produce electricity or heat. Manure that has been digested still retains almost all of the nutrients it had before digestion. Digested manure is usually held in a storage structure until it can be applied to crop fields. Photo 1 (below) shows a complete mix digester on a pig farm.
Some pig farms handle manure as a solid. Photo 2 (below) shows a farm with around 1,000 pigs housed in several hoop buildings. Bedding is added to the barn at regular intervals and a manure pack develops. New bedding on top keeps the animals dry and comfortable. The manure and used bedding from these barns is collected and stored as a solid manure. In Photo 2, you can see the stockpile of manure recently cleaned out of the building and the new bedding waiting to be placed inside. Solid manure from pig farms can be stored and used like solid manure from other types of livestock operations (e.g., land application, compost, etc.).