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Pork production is an important component of American agriculture and an important part of the American diet and way of life. Fewer than100,000 farms were producing pork in 2000 with production is concentrated in the Corn Belt states and in North Carolina.
Modern pork production is mostly done in enclosed buildings to protect animals from the weather, from predators and from the spread of diseases. While larger operations enabled farmers to significantly increase the efficiency of production using less labor, it resulted in environmental challenges with larger amounts of manure concentrated in a small area.
This module will look at pork production as it has evolved over the past 300 years in the U.S., at the economic value of pork to the U.S. and American agriculture and at typical production and manure handling systems in use today.
- Background of Pork Production in U.S.
- Products from Pork
- Pork Production Phases
- Production Systems
- Common Manure Handling Systems
- Potential Environmental Impacts
- Study Questions
Background of Pork Production in U.S.
Wild boars domesticated in N. Europe c.1500 B.C., are believed to be the ancestor of modern domesticated hogs, along with a genetic input from smaller Asian species domesticated in China around 3000 B.C. Pork, the meat from swine, was widely consumed throughout the ancient world and the Roman Empire. Pigs were not indigenous to the Americas, but came from Europe and the Orient. Columbus brought hogs on his second voyage to the Americas in 1493. Polynesians may have brought pigs from the Orient to the Hawaiian Islands even earlier.For much of the 19th and 20th centuries, pork was the preferred meat in the U.S. Hogs were valued not just for their meat but for the lard, which was used for everything from cooking and lamp oil to baking and making candles and soap. As Americans became more health conscious, they lost much of their appetite for animal fats, switching to more healthy vegetable oils. Production began to focus on the pigs’ ability to efficiently convert feed into protein, which resulted in a much leaner type of pig being produced.
There has also been a significant change in how and where hogs are produced
in the U.S. over the past 50 years. Low consumer prices, and therefore
low producer prices, have resulted in larger, more efficient operations,
with many smaller farms no longer able to produce pigs profitably.
In 1997, sales of all animals in the U.S. totaled over $75 billion. Currently, most of the swine in the United States are produced in North Carolina and the Midwestern and plains states, including Nebraska, Iowa, Minnesota, Missouri, Indiana and Illinois. Worldwide, China is by far the largest producer of pork, producing nearly four times as much as the U.S.
There are many breeds of swine, such as Hampshire, Duroc, Poland, China,
Landrace, etc., but most farms use crossbreeds to try to gain the best
traits of each breed.
Products from Pork
Pork is the most widely consumed meat in the world. People eat many different pork products, such as bacon, sausage, pork chops and ham. A 250-pound market hog yields about 150 pounds of pork.
Several valuable products or by-products, in addition to meat, come from swine. These include insulin for the regulation of diabetes; valves for human heart surgery; suede for shoes and clothing; and gelatin for many food and non-food uses. Swine by-products are also important parts of such products as water filters, insulation, rubber, antifreeze, certain plastics, floor waxes, crayons, chalk, adhesives and fertilizer.
Swine production can be logically separated into a number of phases, beginning with the sow being bred. Historically, this has been done by placing a number of sows in a pen with one or more boars. In confinement buildings, boars are often rotated between sow pens to make sure that all sows are bred while they were in heat. Sows in enclosed shelters come into estrous, 3 until 5 days after their pigs are weaned. The estrous period, or standing heat, is the period when the sow can be bred. Estrous only lasts a short time, so it is critical that the sow is bred at this time. During estrous, the sow shows outward signs of being willing to accept the boar, such as standing still when the producer applies downward pressure on her back or holding her ears erect. If the sow is not bred during this period, she normally returns to estrous about 21 days later. These two periods are known as "first heat breeding" and "second heat breeding". The non-pregnant sow is considered "unproductive" during this 3-week period, since she still must be fed and housed. Most modern operations have sows bred only on first heat. Sows that fail to breed during this estrous are often sent to market and replaced in the sow herd by gilts, or young females that are removed from the grow-finish group of pigs. After breeding, the sow "gestates" her "litter" for 113 to 116 days before the pigs are born or "farrowed." A good way to remember gestation length for swine is that it is approximately "3 months, 3 weeks and 3 days".
An average sow will raise three to five litters of pigs in her lifetime. Sows may be culled and sent to market, because of age, health problems, failure to conceive, or if they are able to raise only a low number of pigs per litter.
Pigs are born with eight needle-sharp teeth and curly tails. The tips of the teeth are clipped at birth to prevent injury to the sow's utter and other piglets and the tail is shortened to prevent tail biting. Piglets weigh about three pounds at birth and are weaned from the sow at anywhere from five days to four weeks, with most operations weaning pigs at two to three weeks.
After weaning, pigs are normally placed in a "nursery" where they are kept in a temperature-controlled environment, usually on slotted floors. The floors in a nursery are usually constructed from plastic or plastic covered steel instead of concrete to provide additional comfort for the small pigs. Pigs are normally given around three square feet of space each and provided with ready access to water and feed. Nursery pens are sometimes elevated, with their slotted floor above the room floor level 8 to 12 inches. This is done to minimize the possibility of cold floor drafts chilling the young pigs. Immediately after weaning, the temperature in the nursery may be as much as 85 degrees, and then dropped gradually to about 70 degrees as the pigs grow. Pigs are normally removed from the nursery at about 6 to 10 weeks of age and placed in a "grow-finishing" building. Nursery rooms are almost always heated with furnaces and ventilated with mechanical fans, controlled by a thermostat, in order to keep the pigs warm and dry throughout the year.
This phase is where pigs are fed as much as they wish to eat until they reach market weight of 250 to 275 pounds and provided around 8 sq. ft. of space per pig. Marketing normally occurs at five to six months of age, depending on genetics and any disease problems encountered. Some gilts are returned from the grow-finish phase to the sow herd for breeding purposes, to replace older sows that are culled.
Animals in a grow-finish operation are larger and produce a great deal of body heat. Ventilation to keep the animals cool is usually more of a concern than providing heat in winter. Animals at this age grow best at around 60-70 degrees. In winter, they are protected from winter winds in a moderately well insulated building. Enough ventilation must be provided to remove moisture and to provide fresh air for the animals. In summer, large sidewall vents are opened or large ventilation fans are operated to keep the animals comfortable. This is referred to, respectively, as naturally ventilated (air change due to the wind) or mechanically ventilated (where air is drawn into the buildings through vents due to a negative pressure created with wall fans that exhaust inside air.
Before the 1960s, most pork in the U.S. was raised in outside lots or on pasture systems. With the development of slotted floors and liquid manure handling equipment, it became possible for producers to more easily care for larger numbers of animals, and to do so protected from the weather. Enclosed buildings overcame most weather problems, predators and minimized the potential pollution from outside lot runoff. It also made it practical to farrow sows twice a year, rather than once. This was the beginning of intensive production schedules on relatively small areas as found throughout the world today.
In a continuous flow barn, animals of many different stages of development may be housed in close proximity to one another and the facilities are never empty. Advantages are that space is efficiently used, because pigs can be moved to larger pens as they grow, and new arrivals replace them in the smaller pens. Continuous systems also simple to plan; if the producer wants to wean two litters each week, two sows must be bred each week.
Disadvantages are that different ages of animals (with different degrees of disease resistance) are housed together, facilitating disease spread, stress levels can be heightened with changing social groups, adequate cleaning and disinfecting are not feasible, and higher levels of antibiotics and other medications are normally required to control disease.
Most swine today are raised in “all-in, all-out” (AIAO) systems, where each room or building is completely emptied and sanitized between groups of pigs. Each new group of pigs enters a freshly disinfected environment, and stays there for this phase of their life. The facility has a separate room or building for each group of pigs weaned, with extra space if needed to allow workers time to clean the room before the next group of pigs. AIAO animals in each room are of a uniform age and size and are isolated to the extent possible to decrease the possibility of diseases spreading from older animal groups to younger ones.
The primary advantages are that disease spread can be better contained, animals are less stressed because they remain with the same age and social group throughout their development, and complete cleaning and disinfecting between groups is possible. The disadvantage is that space is less efficiently allocated, and that more space may be needed to allow rooms to be empty for cleaning between groups.
Until around 1990, swine production systems were usually housed on a single site, because of labor savings and convenience. Health concerns have since caused many swine operations to house the various production phases at different sites to further minimize contact between pigs of different ages. This is either a two-site or a three-site system. A two-site system has breeding and gestation at one site and farrowing/nursery and grow finish pigs at a separate site, while a three site also places the nursery at a separate site.
In the last few years, some producers have constructed “wean to finish” barns where pigs go immediately after weaning, and stay until market. This combines the nursery and grow-finish phases of production. These barns provide substantially more space per pig than is needed initially, but provide the advantage of only moving pigs once during their lifetime. This reduces stress on the animals and saves labor since buildings are not cleaned until the hogs are marketed.
Swine have a digestive system similar to humans and different from ruminants such as cattle and sheep, which can eat forages or grasses. Pigs are fed a diet that is primarily ground corn to supply heat and energy and soybean meal to provide protein. Vitamins and minerals are also added in their feed. Rations are closely tailored to optimize health and growth at each stage in their life. Many producers even modify the ration based on the pig’s gender.
The ration is normally changed to provide more energy and less protein as the pig grows. The goal is to optimize feed utilization for different stages of growth. Since nutritional needs are different for male and female grow-finish pigs, larger operations may even modify the ration, based on gender. Recent studies indicate that ration modifications that can reduce the amount of nitrogen and phosphorous excreted in the manure, while maintaining optimum pig growth and health. It takes nearly 1000 pounds of feed to raise a hog to market weight. This same pig drinks about one-and-a-half to two gallons of water a day over its six-month life.
Swine manure was historically handled as a solid, either deposited directly by grazing animals, or collected in bedding placed on solid shelter floors to absorb the urine. Pastured animals spread the manure over the land as they grazed. Manure deposited on solid floors is typically stored where it falls, with more bedding added as needed to maintain a dry floor. Liquid drains away from the manure dropped on an outside lot and must be collected in a storage, leaving the solid manure behind. The manure composts in place somewhat and is removed every few months. Fertilizer value is recovered by spreading on cropland to complete the nutrient cycle. Solid manure is normally surface applied, but in some cases may be incorporated into the soil with a farm tillage operation shortly after spreading. Composting is another option for solid manure management.
Manure is typically scraped from outside lots every week or two and stacked until it can be hauled to cropland. It is important to keep an outside lot relatively free of manure to control odor and so that rainfall runoff stays mostly free of manure. This facilitates storage of relatively clean runoff for irrigation onto cropland. It is even possible to divert runoff from small operations directly to pasture or to a vegetated filter strip where it can infiltrate. It must be prevented from entering waterways. Clean upslope water and roof water should be diverted away from the open lot to minimize the amount of wastewater that must be handled as a manure.
Most swine manure is handled as a liquid. Manure typically falls through a slotted floor (with the size of slot depending on the size and age of animal) into either a gutter or a concrete storage pit. Storage pits provides from 3-12 months storage of the manure. This pit may either be located directly under the slotted floor and may be from 4' to 10' deep. In some operations, the manure falls into a shallow pit or gutter which is periodically pumped, flushed or drained to a large outside storage. The outside storage may either be constructed in the earth or a commercial steel or concrete storage purchased and erected onsite . Storage size is dictated by regulatory agencies in most states and are usually sized large enough to hold at least six month’s accumulation in Midwestern states. This avoids the need to apply manure during the crop growing season and when weather conditions are unsuitable – such as on frozen ground or when the soil is wet enough that heavy application vehicles could compact and damage the soil for crop production.
Liquid manure from storage is normally agitated thoroughly to make the manure nutrient content between loads more uniform and hauled to the field for application in large tanker wagons or trucks. Liquid manure is either applied to the soil surface or is incorporated during or shortly after application to control loss of volatile ammonia and release of odors. Incorporation is very effective at controlling runoff of manure nutrients and reducing odor from land application if done during or within a few hours after application. One method is a soil injector, where liquid manure is “injected” directly into the soil to a depth of 6 to 9” as the tanker passes over the field. This immediate contact between the manure and soil is highly effective at controlling odor.
In remote areas, liquid manure may be pumped to the land application site
and then irrigated onto cropland. Spray irrigating liquid manure is
a very efficient method of land application, in terms of speed and labor,
but odor emissions can be significant; therefore, it is not feasible to
use this method in populated areas.
Lagoons are different from liquid manure storage because they are operated
to encourage anaerobic digestion of organic material while it is being stored.
This reduces odor when the treated manure is land applied. A properly designed
and operated treatment lagoon is much larger and more expensive than a liquid
manure storage with the same storage time, and the organic solids are much
less concentrated in the liquid.
In the Midwest, an equal part of relatively clean dilution water must be added for each part manure. Furthermore, manure must be added slowly and uniformly to the lagoon, to avoid an upset (and subsequent release of odors) to the biological treatment system. One common method of doing this is to utilize shallow pits or gutters under slotted floors and drain or flush manure to the lagoon on a frequent basis, usually every three days to three weeks. This is done by simply pulling a plug in the bottom of the pit, called gravity drain, use of a scraper system running in the underfloor gutter, through a process called a "hairpen" gutter or by recirculating a volume of relatively clean effluent from the lagoon to flush manure out of the building and into the lagoon. Recirculation involves either a flushing action that takes place several times a day or a "pit recharge" system that works basically like a toilet that is flushed every few days.
A portion of the lagoon contents or "minimum design volume" must be left in the lagoon after its contents are pumped to the land to provide a large number of microbial organisms to treat the new manure entering the system. In spite of proper operation, there is an “over turning” of the lagoon contents that occurs in the fall of the year for a couple of weeks, as ambient temperature drops and cools the top layer of liquid in the lagoon. As its density increases, it “overturns” or drops to the bottom of the lagoon, forcing the bottom layer, containing partially digested manure solids, to the top. This phenomenon results in higher odor levels for a week or two around the lagoon. Multiple Lagoons in series normally emit fewer odors than single cell lagoons.
Lagoon contents are normally applied to cropland by spray irrigation systems.
If the lagoon is properly designed and operated, spray irrigation should
not release much odor because most of the organic solids should have been
biologically degraded. In a well-operated lagoon, typical effluent
should have only about 20% as much nitrogen (N) and about 30% to 40% as
much phosphorous (P) and potassium (K) as the raw manure, because of treatment
and sedimentation of solids to the bottom of the lagoon. Note that
the P and K "lost" actually accumulate in the sludge and must
be utilized properly when removed. These solids, or sludge, must be removed
every few years and the operation should plan to handle them as a part of
their nutrient management plan. Because this material is more concentrated,
it may be practical to haul the sludge off site to more distant cropland
that can better utilize the nutrients contained in the sludge. Because
of the nuisance potential of this partially stabilized material, it should
be incorporated as a liquid manure if possible.
(Adapted in part from Livestock and Poultry Environmental Stewardship Curriculum, MidWest Plan Service; and Proposed US EPA Confined Feeding Rule.)
USEPA's 1998 National Water Quality Inventory indicates that agricultural operations, including animal feeding operations (AFOs), are a significant source of water pollution in the U.S. States estimate that agriculture contributes in part to the impairment of at least 170,750 river miles, 2,417,801 lake acres, and 1,827 estuary square miles (Table 1). Agriculture was reported to be the most common pollutant of rivers and streams.
However, one should not overlook the many positive environmental benefits of agriculture. For example, agricultural practices that conserve soil and increase productivity while improving soil quality also increase the amount of carbon-rich organic matter in soils, thereby providing a global depository for carbon dioxide drawn from the atmosphere by growing plants. The same farming practices that promote soil conservation also decrease the amount of carbon dioxide accumulating in the atmosphere and threatening global warming.
Other benefits compared to urban or industrial land use include greatly reduced storm runoff, groundwater recharge and water purification as infiltrating surface water filters through plant residue, roots and several feet of soil to reach groundwater.
In many watersheds, animal manures represent a significant portion of the total fertilizer nutrients added. In a few counties, with heavy concentrations of livestock and poultry, nutrients from confined animals exceed the uptake potential of non-legume harvested cropland and hayland. USDA estimates that recoverable manure nitrogen exceeds crop system needs in 266 of 3,141 counties in the U.S. (8%) and that recoverable manure phosphorus exceeds crop system needs in 485 counties (15%). It should be pointed out that while legumes are able to produce their own nitrogen, they will use applied nitrogen instead if it is available. The USDA analysis does not consider actual manure management practices used or transport of applied nutrients outside the county; however, it is a useful indicator of excess nutrients on a broad scale. Whole-farm nutrient balance is a very useful tool to identify potential areas of excess.
Air emissions from Animal Feeding Operations (AFO) can be odorous. Furthermore, volatilized ammonia can be redeposited on the earth and contribute to eutrophication of surface waters.
Animal manures are a valuable fertilizer and soil conditioner, if applied under proper conditions at crop nutrient requirements. Potential sources of manure pollution include open feedlots, pastures, treatment lagoons, manure stockpiles or storage, and land application fields. Oxygen-demanding substances, ammonia, nutrients (particularly nitrogen and phosphorus), solids, pathogens, and odorous compounds are the pollutants most commonly associated with manure. Manure is also a potential source of salts and trace metals, and to a lesser extent, antibiotics, pesticides and hormones. This problem has been magnified as poultry and livestock production has become more concentrated. AFO pollutants can impact surface water, groundwater, air, and soil. In surface water, manure's oxygen demand and ammonia content can result in fish kills and reduced biodiversity. Solids can increase turbidity and smother benthic organisms. Nitrogen and phosphorus can contribute to eutrophication and associated algae blooms which can produce negative aesthetic impacts and increase drinking water treatment costs. Turbidity from the blooms can reduce penetration of sunlight in the water column and thereby limit growth of seagrass beds and other submerged aquatic vegetation, which serve as critical habitat for fish, crabs, and other aquatic organisms. Decay of the algae (as well as night-time algal respiration) can lead to depressed oxygen levels, which can result in fish kills and reduced biodiversity. Eutrophication is also a factor in blooms of toxic algae and other toxic estuarine microorganisms, such as Pfiesteria piscicida. These organisms can impact human health as well as animal health. Human and animal health can also be impacted by pathogens and nitrogen in animal manure. Nitrogen is easily transformed into the nitrate form and if transported to drinking water sources can result in potentially fatal health risks to infants. Trace elements in manure may also present human and ecological risks. Salts can contribute to salinization and disruption of the ecosystem. Antibiotics, pesticides, and hormones may have low-level, long-term ecosystem effects.
In ground water, pathogens and nitrates from manure can impact human health via drinking water. Nitrate contamination is more prevalent in ground waters than surface waters. According to the U.S. EPA, nitrate is the most widespread agricultural contaminant in drinking water wells, and nearly 2% of our population (1.5 million people) is exposed to elevated nitrate levels from drinking water wells.
|Total Quantity in US||Amount of Waters Surveyed||Quantity Impaired by All Sources||Quantity Impaired by Agriculture|
|23% of total
|36% of surveyed
|59% of impaired
|Lakes, Ponds, and Reservoirs
|42% of total
|39% of surveyed
|31% of impaired
90,500 square miles
|32% of total
28,889 square miles
|38% of surveyed
11,025 square miles
|15% of impaired
1,827 square miles
Table 2 lists the leading pollutants impairing surface water quality in the U.S. Agricultural production is a potential source of most of these.
Table 2. Five Leading Pollutants Causing Water Quality Impairment in the U.S.
(Percent of incidence of each pollutant is shown in parentheses. For example, siltation is listed as a cause of impairment in 38% of impaired river miles.)
|1||Siltation (38%)||Nutrients (44%)||Pathogens (47%)|
|2||Pathogens (36%)||Metals (27%)||Oxygen-Depleting Substances (42%)|
|3||Nutrients (29%)||Siltation (15%)||Metals (23%)|
|4||Oxygen-Depleting Substances (23%)||Oxygen-Depleting Substances (14%)||Nutrients (23%)|
|5||Metals (21%)||Suspended Solids (10%)||Thermal Modifications (18%)|
List of Contaminants in Animal Manure:
- Oxygen-Demanding Substances
- Antibiotics, Pesticides, and Hormones
- Airborne Emissions from Animal Production Systems
- Comprehensive Nutrient Management Planning
- Study Questions
When discharged to surface water, biodegradable material is decomposed by aquatic bacteria and other microorganisms. During this process, dissolved oxygen is consumed, reducing the amount available for aquatic animals. Severe depressions in dissolved oxygen levels can result in fish kills. There are numerous examples nationwide of fish kills resulting from manure discharges and runoff from various types of AFOs.
Manure may be deposited directly into surface waters by grazing animals. Manually-collected manure may also be introduced into surface waters. This is typically via storage structure failure, overflow, operator error, etc.
Manure can also enter surface waters via runoff if it is over-applied or misapplied to land. For example, manure application to saturated or frozen soils may result in a discharge to surface waters. Factors that promote runoff to surface waters are steep land slope, high rainfall, low soil porosity, and proximity to surface waters. Incorporation of the manure into the soil decreases runoff.
Nitrogen (N) is an essential nutrient required by all living organisms. It is ubiquitous in the environment, accounting for 78 percent of the atmosphere as elemental nitrogen (N2). This form of nitrogen is inert and does not impact environmental quality since it is not bioavailable to most organisms and therefore has no fertilizer value. Nitrogen can form other compounds, however, which are bioavailable, mobile, and potentially harmful to the environment. The nitrogen cycle shows the various forms of nitrogen and the processes by which they are transformed and lost to the environment.
Nitrogen in manure is primarily in the form of organic nitrogen and ammonia nitrogen compounds. In its organic form, nitrogen is unavailable to plants. However, organic nitrogen can be transformed into ammonium (NH4+) and nitrate (NO3-) forms, via microbial processes which are bioavailable and have fertilizer value. These forms can also produce negative environmental impacts when they are transported in the environment.
"Ammonia-nitrogen" includes the ionized form (ammonium, NH4+) and the un-ionized form (ammonia, NH3). Ammonium is produced when microorganisms break down organic nitrogen products such as urea and proteins in manure. This decomposition occurs in both aerobic and anaerobic environments. In solution, ammonium is in chemical equilibrium with ammonia.
Ammonia exerts a direct biochemical oxygen demand (BOD) on the receiving water since dissolved oxygen is consumed as ammonia is oxidized. Moderate depressions of dissolved oxygen are associated with reduced species diversity, while more severe depressions can produce fish kills.
Additionally, ammonia can lead to eutrophication, or nutrient over-enrichment, of surface waters. While nutrients are necessary for a healthy ecosystem, the overabundance of nutrients (particularly nitrogen and phosphorus) can lead to nuisance algae blooms.
Pfiesteria often lives as a nontoxic predatory animal, becoming toxic in response to fish excretions or secretions (NCSU, 1998). While nutrient-enriched conditions are not required for toxic outbreaks to occur, excessive nutrient loadings can help create an environment rich in microbial prey and organic matter that Pfiesteria uses as a food supply. By increasing the concentration of Pfiesteria, nutrient loads increase the likelihood of a toxic outbreak (Citizens Pfiesteria Action Commission, 1997).
The degree of ammonia volatilization is dependent on the manure management system. For example, losses are greater when manure remains on the land surface rather than being incorporated into the soil, and are particularly high when the manure is spray irrigated onto land. Environmental conditions also affect the extent of volatilization. For example, losses are greater at higher pH levels, warmer temperatures and drier conditions, and in soils with low cation exchange capacity, such as sands. Losses are decreased by the presence of growing plants. (Follett, 1995)
Nitrifying bacteria can oxidize ammonium to nitrite (NO2-) and then to nitrate (NO3-). Nitrite is toxic to most fish and other aquatic species, but it typically does not accumulate in the environment because it is rapidly transformed to nitrate in an aerobic environment. Alternatively, nitrite (and nitrate) can undergo bacterial denitrification in an anoxic environment. In denitrification, nitrate is converted to nitrite, and then further converted to gaseous forms of nitrogen - elemental nitrogen (N2), nitrous oxide (N2O), nitric oxide (NO), and/or other nitrogen oxide (NOx) compounds. Nitrification occurs readily in the aerobic environments of receiving streams and dry soils while denitrification can be significant in anoxic bottom waters and saturated soils.
Nitrate is a useful form of nitrogen because it is biologically available to plants and is therefore a valuable fertilizer. However, excessive levels of nitrate in drinking water can produce negative health impacts on infant humans and animals. Nitrate poisoning affects infants by reducing the oxygen-carrying capacity of the blood. The resulting oxygen starvation can be fatal. Nitrate poisoning, or methemoglobinemia, is commonly referred to as "blue baby syndrome" because the lack of oxygen can cause the skin to appear bluish in color. To protect human health, EPA has set a drinking water Maximum Contaminant Level (MCL) of 10 mg/l for nitrate-nitrogen. Once a water source is contaminated, the costs of protecting consumers from nitrate exposure can be significant. Nitrate is not removed by conventional drinking water treatment processes; its removal requires additional, relatively expensive treatment units.
Nitrogen in livestock manure is almost always in the organic, ammonia or ammonium form but may become oxidized to nitrate after being diluted. It can reach surface waters via direct discharge of animal wastes. Lagoon leachate and land-applied manure can also contribute nitrogen to surface and ground waters. Nitrate is water soluble and moves freely through most soils. Nitrate contributions to surface water from agriculture are primarily from groundwater connections and other subsurface flows rather than overland runoff (Follett, 1995).
Animal wastes contain both organic and inorganic forms of phosphorus (P). As with nitrogen, the organic form must mineralize to the inorganic form to become available to plants. This occurs as the manure ages and the organic P hydrolyzes to inorganic forms. The phosphorus cycle is much simpler than the nitrogen cycle because phosphorus lacks an atmospheric connection and is less subject to biological transformation.
Phosphorus is of concern in surface waters because it can lead to eutrophication. Phosphorus is also a concern because phosphate levels greater than 1.0 mg/l may interfere with coagulation in drinking water treatment plants (Bartenhagen et al., 1994). A number of research studies are currently underway to decrease the amount of P in livestock manure, primarily through enzymes and animal ration modifications that make phosphorous in the feed more available (and usable) by the animal. This means that less phosphorus must be fed to ensure an adequate amount for the animal and, as a result, less phosphorous is excreted in the manure.
Phosphorus predominantly reaches surface waters via direct discharge and runoff from land application of fertilizers and animal manure. Once in receiving waters, the phosphorus can become available to aquatic plants. Land-applied phosphorus is much less mobile than nitrogen since the mineralized form (inorganic Phosphate) is easily adsorbed to soil particles. For this reason, most agricultural phosphorus control measures have focused on soil erosion control to limit transport of particulate phosphorus. However, soils do not have infinite phosphate adsorption capacity and with long-term over-application, inorganic phosphates can eventually enter waterways even if soil erosion is controlled.
Both manure and animal carcasses contain pathogens (disease-causing organisms) which can impact human health, other livestock, aquatic life, and wildlife when introduced into the environment. Several pathogenic organisms found in manure can infect humans.
Table 1. Some Diseases and Parasites Transmittable to Humans from Animal Manure
|Anthrax||Bacillus anthracis||Skin sores, fever, chills, lethargy, headache, nausea, vomiting, shortness of breath, cough, nose/throat congestion, pneumonia, joint stiffness, joint pain|
|Brucellosis||Brucella abortus, Brucella melitensis, Brucella suis||Weakness, lethargy, fever, chills, sweating, headache|
|Colibaciliosis||Escherichia coli (some serotypes)||Diarrhea, abdominal gas|
|Coliform mastitis-metritis||Escherichia coli (some serotypes)||Diarrhea, abdominal gas|
|Erysipelas||Erysipelothrix rhusiopathiae||Skin inflammation, rash, facial swelling, fever, chills, sweating, joint stiffness, muscle aches, headache, nausea, vomiting|
|Leptospirosis||Leptospira Pomona||Abdominal pain, muscle pain, vomiting, fever|
|Listeriosis||Listeria monocytogenes||Fever, fatigue, nausea, vomiting, diarrhea|
|Salmonellosis||Salmonella species||Abdominal pain, diarrhea, nausea, chills, fever, headache|
|Tetanus||Clostridium tetani||Violent muscle spasms, “lockjaw” spasms of jaw muscles, difficulty breathing|
|Tuberculosis||Mycobacterium tuberculosis, Mycobacterium avium||Cough, fatigue, fever, pain in chest, back, and/or kidneys|
|Q fever||Coxiella burneti||Fever, headache, muscle pains, joint pain, dry cough, chest pain, abdominal pain, jaundice|
|Foot and Mouth||Virus||Rash, sore throat, fever|
|Coccidioidycosis||Coccidioides immitus||Cough, chest pain, fever, chills, sweating, headache, muscle stiffness, joint stiffness, rash wheezing|
|Histoplasmosis||Histoplasma capsulatum||Fever, chills, muscle ache, muscle stiffness, cough, rash, joint pain, join stiffness|
|Ringworm||Various microsporum and trichophyton||Itching, rash|
|Coccidiosis||Eimeria species||Diarrhea, abdominal gas|
|Cryptosporidiosis||Cryptosporidium species||Watery diarrhea, dehydration, weakness, abdominal cramping|
|Giardiasis||Giardia lamblia||Diarrhea, abdominal pain, abdominal gas, nausea, vomiting, headache, fever|
|Toxoplasmosis||Toxoplasma species||Headache, lethargy, seizures, reduced cognitive function|
|Ascariasis||Ascaris lumbricoides||Worms in stool or vomit, fever, cough, abdominal pain, bloody sputum, wheezing, skin rash, shortness of breath|
|Sarcocystiasis||Sarcosystis species||Fever, diarrhea, abdominal pain|
The treatment of public water supplies reduces the risk of infection via drinking water. However, protecting source water is the best way to ensure safe drinking water. Cryptosporidium parvum, a protozoan that can produce gastrointestinal illness, is a concern, since it is resistant to conventional treatment. Healthy people typically recover relatively quickly from such illnesses. However, they can be fatal in people with weakened immune systems such as the elderly and small children.
Runoff from fields where manure has been applied can be a source of pathogen contamination, particularly if a rainfall event occurs soon after application. The natural filtering and adsorption action of soils typically strands microorganisms in land-applied manure near the soil surface (Crane et al., 1980). This protects underlying groundwater, but increases the likelihood of runoff losses to surface waters. Depending on soil type and operating conditions, however, subsurface flows can be a mechanism for pathogen transport.
Soil type, manure application rate, and soil pH are dominating factors in bacteria survival (Dazzo et al., 1973; Ellis and McCalla, 1976; Morrison and Martin, 1977; Van Donsel et al., 1967). Experiments on land-applied poultry manure have indicated that the population of fecal organisms decreases rapidly as the manure is heated, dried, or exposed to sunlight on the soil surface (Crane et al., 1980).
Antibiotics, Pesticides, and Hormones
Antibiotics, pesticides, and hormones are organic compounds which are used in animal feeding operations and may pose risks if they enter the environment. For example, chronic toxicity may result from low-level discharges of antibiotics and pesticides. Estrogen hormones have been implicated in the reduction in sperm counts among Western men (Sharpe and Skakkebaek, 1993) and reproductive disorders in a variety of wildlife (Colburn et al., 1993). Other sources of antibiotics and hormones include municipal waste waters, septic tank leachate, and runoff from land-applied sewage sludge. Sources of pesticides include crop runoff and urban runoff.
Little information is available regarding the concentrations of these compounds in animal wastes, or their fate/transport behavior and bioavailability in waste-amended soils. These compounds may reach surface waters via runoff from land-application sites.
With the trend toward larger, more concentrated production operations, odors and other airborne emissions are rapidly becoming an important issue for agricultural producers.
Whether there is a direct impact of airborne emissions from animal operations on human health is still being debated. There are anecdotal reports about health problems and quality-of-life factors for those living near animal facilities have been documented.
Source of Airborne Emissions
Odor emissions from animal production systems originate from three primary sources: manure storage facilities, animal housing, and land application of manure.
In an odor study in a United Kingdom county (Hardwick 1985), 50% of all odor complaints were traced back to land application of manure, about 20% were from manure storage facilities, and another 25% were from animal production buildings. Other sources include feed production, processing centers, and silage storage. With the increased use of manure injection for land application, and longer manure storage times, there may be a higher percentage of complaints in the future associated with manure storage facilities and animal buildings and less from land application.
Animal wastes include manure (feces and urine), spilled feed and water, bedding materials (i.e., straw, sunflower hulls, wood shaving), wash water, and other wastes. This highly organic mixture includes carbohydrates, fats, proteins, and other nutrients that are readily degradable by microorganisms under a wide variety of suitable environments. Moisture content and temperature also affect the rate of microbial decomposition.
A large number of volatile compounds have been identified as byproducts of animal waste decomposition. O'Neill and Phillips (1992) compiled a list of 168 different gas compounds identified in swine and poultry wastes. Some of the gases (ammonia, methane, and carbon dioxide) also have implications for global warming and acid rain issues. It has been estimated that one third of the methane produced each year comes from industrial sources, one third from natural sources, and one third from agriculture (primarily animals and manure storage units). Although animals produce more carbon dioxide than methane, methane has as much as 15 times more impact on the greenhouse effect than carbon dioxide.
Dust, pathogens, and flies are from animal operations also airborne emission concerns. Dust, a combination of manure solids, dander, feathers, hair, and feed, is very difficult to eliminate from animal production units. It is typically more of a problem in buildings that have solid floors and use bedding as opposed to slotted floors and liquid manure. Concentrations inside animal buildings and near outdoor feedlots have been measured in a few studies; however, dust emission rates from animal production are mostly unknown.
Pathogens are another airborne emission concern. Although pathogens are present in buildings and manure storage units, they typically do not survive aerosolization well, but some may be transported by dust particles.
Flies are an additional concern from certain types of poultry and livestock operations. The housefly completes a cycle from egg to adult in 6 to 7 days when temperatures are 80 to 90°F. Females can produce 600 to 800 eggs, larvae can survive burial at depths up to 4 feet, and adults can fly up to 20 miles. Large populations of flies can be produced relatively quickly if the correct environment is provided. Flies tend to proliferate in moist animal production areas with low animal traffic.
Emission Movement or Dispersion
The movement or dispersion of airborne emissions from animal production facilities is difficult to predict and is affected by many factors including topography, prevailing winds, and building orientation. Prevailing winds must be considered to minimize odor transport to close or sensitive neighbors. A number of dispersion models have been developed to Airborne Emission Regulations.
Most states and local units of government deal with agricultural air quality issues through zoning or land use ordinances. Setback distances may be required for a given size operation or for land application of manure. A few states (for example, Minnesota) have an ambient gas concentration (H2S for Minnesota) standard at the property line. Gas and odor standards are difficult to enforce since on-site measurements of gases and especially odor are hard to do with any high degree of accuracy. Producers should be aware of odor- or dust-related emissions regulations applicable to their livestock operation.
Source: Lesson 40 of the LPES: Adapted from Livestock and Poultry Environmental Stewardship curriculum, lesson authored by Larry Jacobson, University of Minnesota; Jeff Lorimor, Iowa State University; Jose Bicudo, University of Kentucky; and David Schmidt, University of Minnesota, courtesy of MidWest Plan Service, Iowa State University, Ames, Iowa 50011-3080, Copyright (c) 2001.
Environmental Impacts of Animal Feeding Operations Study Questions
Identify the definition that best fits the following terms:
Comprehensive Nutrient Management Planning
Recently, the concept of Comprehensive Nutrient Management Planning (CNMP) was introduced by the U. S. Environmental Protection Agency (EPA) and U.S. Department of Agriculture’s (USDA’s) Natural Resources Conservation Service (NRCS). It is anticipated that the CNMP will serve as a cornerstone of environmental plans assembled by animal feeding operations to address federal and state regulations. EPA and NRCS guidelines for CNMP are given in Table 1.
|Table 1. Summary of Issues addressed by a CNMP as initially definied by EPA's Guidance|
|Planning components of CNMP||Issues addressed|
|A manure handling and storage plan||
|Land application plan||
|Site management plan||Soil conservation practices that minimize movement of soil and manure components to surface and groundwater|
|Record keeping||Manure production, utilization, and export to off-farm users|
|Other utilization options||Alternative safe manure utilization strategies such as sale of manure, treatment technologies, or energy generation|
|Feed management plan||Alternative feed programs to minimize the nutrients in manure|
Pork Production Study Questions
Identify the definition that best fits the following terms: