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Poultry Production

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Poultry production is an important and diverse component of American agriculture. Poultry products including eggs, chicken and turkey meat are a healthy part of the diets of most Americans. In 1997, nearly 99,700 farms were producing poultry and poultry products (egg, broiler, and turkey; NASS/USDA). While broiler chicken production is concentrated primarily in the southern and southeastern U.S., turkey production occurs primarily in the Corn Belt and in North Carolina. Egg production is distributed throughout the U.S.

Modern poultry production occurs primarily in enclosed buildings to protect the birds from weather, predators, and the spread of diseases from wild birds. This has allowed farmers to greatly increase production efficiency while significantly reducing the amount of labor required. As with pork production, this has resulted in environmental challenges with production of larger volumes of manure in much smaller areas.

This module will cover the modernization of poultry production over the past 60 years, different phases of production and the production systems in which they occur.

Background of Poultry Production in U.S.

Backyard Operations
(Source: J. Sell, Iowa State University)
Chickens are the most numerous birds in the world. The chicken is believed to have been domesticated nearly 5000 years ago from wild birds in Southeast Asia. On the other hand, the domestication of the turkey occurred much more recently, by American Indians in prehistoric times. The turkey was introduced into Europe in the sixteenth century by returning Spanish explorers. Settlers emigrating to the U.S. who later bred this European stock with wild turkeys in the Eastern U.S. to produce the ancestors of today's commercially grown turkeys.

The poultry industry has largely grown from backyard operations which provided supplemental income for the family to a vertically integrated industry. (PDF, 373KB) Exit EPA Poultry consumption in the U.S. has increased from the 1900s, when chicken was eaten only on Sundays to making poultry an every day item today.

  U.S. Broiler Production (1934-99)
Increase in Young Chicken Exports Increase in Young Chicken Exports
(Source: J. Sell, Iowa State University)

U.S. Poultry Inventory
Specie #/year kg
Broiler 8 billion 18.5 billion
Turkey 273 million 3.2 billion
Layers 269 million 72 billion eggs
Ducks 20 million ~ 64 million
per USDA 1999

Broiler production greatly increased throughout the 1980s and 1990s due to Americans becoming more health conscious and through an unprecedented increase in exports. Part of this increase has also been attributed to the poultry industry supplying products that are further processed and easier for the consumer to prepare. These increases have led to an all time high in poultry production in the U.S. (Table). Currently, most poultry production in the United States is in the Southeastern states.

At one time, there were many distinct breeds of chicken, each having particular traits or characteristics. Through selective breeding, only a few strains of birds dominate the market today. There are many primary breeding companies of poultry, but only a handful are responsible for most of the broiler chicken, Exit EPA laying hen, Exit EPA and turkey Exit EPA production in the world.

Concentration and specialization of the poultry industry have led to the development of allied industries. These industries supply housing, feeding and other equipment, hatchery equipment, processing supplies and equipment, drugs and other health products, feed additives, and several other items.

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Products from Poultry

U.S. Per Capita Consumption Poultry Industry Develops New Value-Added Products
(Source: J. Sell, Iowa University)

Distribution of Eggs ProducedPoultry products (broiler meat in particular) has the highest per capita consumption in the United States. People eat many different poultry products, including eggs, turkey ham, buffalo wings, hot dogs, chicken nuggets, chicken-patties, fried, roasted, glazed, marinated, etc. Not all of poultry products, however, are directly consumed by humans. For example, eggs are also used for the production of therapeutic vaccines and are beginning to be used for production of antibodies and pharmacological proteins. Part of the increase in poultry production in the 1980s and 1990s can be attributed to the development of new, further-processed, value-added products. Similarly, the egg market has changed in scope through the late 1980s such that a greater proportion of eggs that are produced are destined for a liquid egg market. Liquid egg is used in a variety of institutions including hotels, restaurants, hospitals, and if dried, included in numerous other products, such as cake mixes. Today, the U.S. produces 33% of the world's broiler meat, 53.7% of the turkey meat, and 11% of the eggs (USDA-FAS, 2001).

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Poultry Production Phases

Poultry production encompasses a number of different species, including the chicken (reared for laying eggs-"layers", or meat production-"broilers"), turkeys, ducks, and other waterfowl and gamebirds. Each species and particular type of production is uniquely different. We will primarily focus on laying hens, broiler production, turkey production, and duck production.

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Breeding Flocks

Lighting and Housing Types

Lighting plays a very important role in bird growth, development, and maturity. Most commercial poultry specie are photosensitive animals. For example, a constant or decreasing amount of daily light (as occurs during the fall and winter months) will delay sexual maturity in growing birds. An increasing amount of light (as occurs in the spring) will stimulate sexual maturity. Since lighting plays such an important role in the development of sexual maturity, adolescent birds are generally reared in black-out houses. This allows the producer to have complete control over the lighting cycle of the birds by providing artificial light.
Breeder Houses - Slat Floor
Housing for Breeder Broilers
(Source: J. Sell, Iowa State University)

Once birds reach the age of sexual maturity, they are moved to the laying house. Breeder broilers and ducks are generally be kept in a barn with a slotted floor or with a wire floor with litter in the middle of the house to act as a mating area. Breeder turkeys are generally reared in all litter houses. Clean, nesting boxes are provided so that the birds may lay their eggs without being disturbed by other birds and so that the eggs may be kept clean and easily collected.

Restricted Feeding

Adolescent broilers (especially), turkeys, and ducks, when given the opportunity, will eat until they become obese. Therefore, restricted feeding is necessary if the birds are going to be used as breeder stock. Otherwise, the obesity severely limits the numbers of eggs laid and the fertility of those eggs. For this reason, restricted feeding is necessary. There are two main types of restrictive feeding programs. The first of these is every day feeding of a limited amount, or lower nutrient content diet. The amount fed will ensure adequate growth but not result in obesity. Another type of restrictive feeding is an every other day feeding program. where birds are fed a specific quantity of feed every other day. Since male broiler chickens grow faster, they often are reared separately from the females until they are moved into the breeder house. Specific ratios of male-to-females are kept in the breeder house (typically, broilers-1 male :15 females, turkeys and ducks-1:8 to 10) to ensure fertility of hatching eggs.


Hatchlings Destined
for Grow-out Facilities
(Source: Purdue University)
Eggs are typically collected from breeder farms, taken to a hatchery and stored from 0 to 10 days prior to being set in an incubator. These eggs will be stored at temperatures between 55-68° F, depending on when they are to be incubated. When the eggs are placed in incubators, embryonic development begins. Different species of birds require different incubation times. Chickens hatch in 21 days while turkeys and ducks need 28 days. The hatchlings (chicks, poults, or ducklings) are processed (vaccinated, gender sorted, and/or other procedures) then transported to commercial grow-out facilities. Transport typically will take anywhere from a few hours to one day.

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Laying Hens

The modern laying hen is a biological marvel. She begins laying eggs at approximately 18 weeks of age and by the end of her first year, she may have produced upwards of 200 eggs - nearly 25 pounds. The hen reaches peak egg production (95 + %) within 4 to 6 weeks after she begins to lay eggs. In order to produce such a hen, it is critical that the hen be carefully managed during her first 17 weeks of life.

At the beginning of a pullet's life in the hatchery, she is vaccinated to prevent future diseases. On the farm, pullets will be grown in cages until they are moved into the laying house at 16 to 17 weeks of age. Pullet chicks will typically be beak trimmed during their first three weeks of life in the pullet house to minimize cannibalism.

Lighting programs are very similar to what was described for breeding flocks.

Induced molting

Molting is the process of the bird shedding and re-growing feathers. Molting occurs naturally in the wild, as seasonal daylight shortens and females stop laying eggs. Laying hens are generally molted once or twice during their productive lives. Molting usually does not affect egg size, but allows for an improved egg laying rate, improved shell quality, and increased albumin height. It also allows a producer to keep the birds longer than they might otherwise be kept. To induce molt, a producer may use a period of fasting and a reduced amount of daylight, giving the birds water and allowing them to lose a proportion of their body weight. Daylight length will then be increased, and the hens begin laying eggs again.

In-line vs. Off-line production

Eggs Refrigerated
In-line Layer Operation
(Source: Purdue University)
Laying hen farms are composed of two different types, in-line and off-line.

In-line production - Hen houses are placed side-by-side and linked by a conveyor belt. The conveyor belt leads to a centralized processing building, where the eggs from all houses are sorted, graded, either packed or broken and further processed, and refrigerated prior to shipping.

Off-line production - This is similar to the in-line production, but the eggs that are collected on a conveyor belt and sent to a main building are packed and refrigerated prior to shipping to another facility to be processed.

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Broilers, Turkeys, Ducks (meat-bird production)

Broilers - Anit-Spill Feeders
(Source: Purdue University)

Brooder Rings Nipple or Cup Waterers
Brooder Rings Keep Broilers
near Heat, Feed and Water
Waterer in Broiler House
(Source: Purdue University) (Source: Purdue University)

Broilers are relatively easy to raise. To begin with, the whole house is heated and brooder rings are placed around each brooder (heating) unit. These rings create a "microclimate" relative to the rest of the room to prevent drafts and keep the birds near each other and near the feed and water. The nipple or cup waterers in each pen must be fully functional and supplemental jug waterers in the brooder rings must be kept filled. When the birds arrive, they are placed into the rings and introduced to the waterers and feed. Feed is placed in the feeders and on paper placed on the floor of the pen to encourage young birds to eat. Generally, broilers are brooded in a portion of the house until a certain age before being given access to the entire barn. These facilities, or "houses" generally have litter floors. Depending on the geographical location of the house, natural ventilation will be either provided by opening curtain-sided walls or large insulated door panels on the sides of the house.

Some farms separate male and female birds, a practice called separate-sex feeding. Separate-sex feeding accomplishes a number of goals. When birds are separated and fed according to gender (versus rearing males and females together), there will be more uniformity among males and among females in the flock. Separation of the birds also allows producers to feed diets that more closely meet the nutritional needs of the male and female birds.

Turkey Housing
(Source: Purdue University)
Turkey Toms - Age to 35 Pounds Chart
(Source: Purdue University)

In previous decades, turkeys have been mainly considered a holiday product. However, with advances of further-processing as well as an increasingly health-conscious population in the U.S., the turkey has become a popular year-round meat. Raising turkeys takes more time than raising broilers, as turkeys take longer to mature. Generally, a turkey is sent to market anywhere between 15 and 25 weeks of age. At 20 weeks of age, a male turkey should weigh about 35-40 pounds.

Poult (baby turkey) - Close-Up
Turkey Poults
(Source: Purdue University)
Getting poults (baby turkeys) started is not as easy as starting broilers. Both benefit from brooder rings in order to keep them close to the heat source, food, and water and to prevent drafts. Additionally, the farm worker must physically show the poults where the water and feed are when placing poults into the brooder rings; otherwise, some birds will never manage to find it.

Poults are usually gender-sorted at the hatchery and the males (toms) and females (hens) are reared separately. They may also toe-trimmed, and beak-trimmed at the hatchery to prevent the birds from injuring each other.

Over their life cycle, turkeys may live in 2 or 3 different barns. The brooder barn, is used for the first 6 to 8 weeks of life. After that, the turkeys may be moved to an intermediate barn. Lastly, they are moved into a grow-out facility. By having multiple barns for different ages, a farm is able to rear a greater number of birds in a shorter amount of time.


While broilers and turkeys may seem like fast-growing birds, the duck is the most rapidly growing animal of all poultry species. A typical duck will weigh 7 pounds in only 6 or 7 weeks!

Ducks can be raised in a number of different types of houses. Some are raised on all-litter floors while others have slats or wire for the flooring. Some houses contain a litter floor with a ramp leading up to raised-wire or expanded plastic flooring over a shallow pit. Since ducks like to play with the watering system (typically a nipple-waterer system), it is located over the raised flooring. Generally, ducks go through two or three stages of housing. Each stage would house anywhere from 13 to 20 groups of ducks per year.

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Production Systems

Old Chicken House Make-Shift Ventilation
Small Poultry Operation with Dirt Floor Make-shift Ventilation
in Poultry House
(Source: J. Sell, Iowa State University) (Source: J. Sell, Iowa State University)

Prior to WWII, the majority of poultry were reared in backyard flocks on dirt-floored pens, in small sheds with natural or make-shift ventilation.

Larger Ventilated Building Large Outdoor Pen
An Early Year-round Production Building Poultry Grown in Large Outdoor Areas
(Source: J. Sell, Iowa State University) (Source: J. Sell, Iowa State University)

Between 1940 and 1960, advancements in nutrition and genetics allowed the broiler market to shift from being able to produce a 3-3.5 pound bird at 16 weeks to one that only took 8 weeks. Due to advances in production efficiency and refrigerated trucking, markets expanded to a much larger geography while the price of poultry per pound dropped dramatically from approximately 65 cents in 1940 to 29 cents in 1960. Due largely to changes in price versus other meat options, demand for broilers increased dramatically. Production systems during this time also underwent dramatic changes from the seasonal, small backyard sheds to large year-round naturally ventilated buildings and during some seasons, large outdoor pens.

Turkeys Broilers - Anit-Spill Feeders
Modern Enclosed Poultry Building On-demand Feeder Line
(Source: Purdue University) (Source: Purdue University)
Chick at Drinking Cup Broiler at Nipple Waterer
On-demand Cup Waterer Nipple Waterer
(Source: Purdue University) (Source: Purdue University)

Today, turkey and broiler flocks are reared in enclosed buildings with updated equipment. For instance, birds are now reared in confinement with on-demand feeder lines, on-demand cup or nipple waterers, or on-demand bell-type waterers. These developments overcame most problems with weather, predators, potential pollution from lot runoff, and allowed the use of more intensive production schedules. Today, almost all turkeys and broilers are reared on litter floors.  Ducks, turkeys, and occasionally broilers are reared in multi-stage facilities with facilities for brooding birds, and in larger facilities (either a separate room or separate building) that they will be moved into at an older age.

Laying Hen in Wire Cages Breeder Houses - Slat Floor
Wire Cages Slotted Floor Facilities
(Source: Purdue University) (Source: Purdue University)

Young pullets, laying hens, and broiler breeders are reared in either wire-cages or slotted-floor systems. If a slotted flooring system is used, there may or may not be a central area containing litter. Duck facilities encompass a number of different production types and may or may not have multistage facilities. Systems in use include all-litter houses, raised-wire flooring over a shallow pit (which would be located below a nipple water line) and houses with raised-wire floors.

Large Ventilation Fans
Ventilated Building
(Source: Purdue University)
Layers in commercial facilities produce a great deal of body heat. Ventilation to keep the hens cool is usually more of a concern than providing heat in winter. Non-brooding birds (3-4 weeks and older) grow best at around 70-75 degrees. In winter, they are protected from winter winds in an insulated building. Enough ventilation must be provided to remove moisture produced by the animals and to provide fresh air. In summer, large sidewall vents are opened or large ventilation fans are operated to keep the animals comfortable. This is referred to as either 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 to the outdoors. Further information on poultry ventilation. Exit EPA

Disadvantages associated with large enclosed, production facilities are that different ages of birds with different degrees of disease resistance are housed in close proximity which can facilitate disease spread if adequate cleaning and disinfecting are not feasible in some situations, and higher levels of medication may be required to control disease. The primary rule of thumb for workers on a farm with multiple ages of birds is to always travel from the youngest birds on the farm to the oldest, and not vice-versa. Biosecurity plans between farms, and between multiple production buildings on the same farm can help reduce the incidence and spread of disease from one flock to the next.

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Feed Conversions per Pound Research and Innovation Have Led to Dramatic Progress in Typical Broiler Performance

Comparison Weight in 1939 and 1993
Improvement in Diet Have Resulted in
Dramatic Improvements in Growth
(Source: J. Sell, Iowa State University)
Poultry in the U.S. are fed diets which are primarily ground corn to supply heat and energy and soybean meal to provide protein. Vitamins and minerals are also added in their feed. It takes only 11.4 pounds of feed to rear a broiler to a 6 pound market weight. This same broiler would drink about 3 gallons of water during this time (approximately 7 weeks). Part of the poultry industry's increase in productiveness has largely been attributed to the efficiency of conversion of feed to gain -or- egg production. This increased efficiency can be largely attributed to improvements in genetics and nutrition.

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Common Manure Handling Systems

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Poultry manure is handled as a solid litter, either deposited directly by animals on pastureland, or collected in bedding placed on solid shelter floors to absorb the urine. Some turkeys, broilers, and ducks are raised on concrete or earthen floors. After every flock, the litter is either:

  1. Removed and fresh litter applied,
  2. Tilled and fresh litter placed on top, or
  3. Cake manure removed, remaining litter tilled or mixed, and fresh litter placed on top. 
Decaker/Cruster Applying Poultry Litter
Tractor-drawn Decaker/Cruster Solid Manure Spreader
(Source: Kelly Manufacturing Co.) (Source: Purdue University)

Cake manure is sometimes removed with a tractor-drawn decaker/cruster which removes the top layer of manure, breaks it apart, and separates the larger manure particles from the finer litter particles (which are placed back into the house).  Poultry litter is normally surface applied, but in some cases may be incorporated into the soil with a farm tillage operation shortly after spreading.

For further information on proper sampling of poultry litter. Exit EPA

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Layer Manure - Dry

Layer Cages Manure is Surface Applied
Laying Hens on Wire Floors Surface Applied Solid Manure
(Source: Purdue University) (Source: Purdue University)

Manure from pullets and laying hens is relatively dry as it falls through layer cages (Figure, above left) into a concrete storage area. Manure composition in these facilities can range in dry matter between 20 and 60 percent. The storage pit provides for long-term storage of the manure.  Manure is then typically surface applied (Figure, above right). Composting is another option for solid manure management.

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Layer Manure - Semi-Solid/Liquid

Some laying hen facilities contain shallow pits with scrapers or belts, or shallow flush pits. This manure typically can not be stacked and requires some type of containment storage. Liquid manure that is mostly water (< 12% solids) must be kept in a watertight storage. Liquid manure can be handled with tank trucks/wagons, injection-type spreaders, or irrigation equipment. Semi-solid manure (12 to 20 percent solids), on the other hand, does not flow readily but still requires containment with walls. This type of manure can be handled easily with bucket loaders and open broadcast spreaders. Most Midwestern states require manure storages for larger operations to be large enough to hold six month’s accumulation. This avoids the need to apply manure during the crop growing season and when weather conditions are unsuitable – such as on frozen or snow-covered ground or when the soil is wet enough that heavy application vehicles could compact and damage the soil.

Agitate Liquid Manure Thoroughly Liquid Manure Applied to Exposed Soil Surface
Liquid Manure Pit Agitation Surface Applied Liquid Manure
(Source: Purdue University) (Source: Purdue University)

Liquid Manure Injected Directly into the Soil
Injecting Liquid Manure
(Source: Purdue University)
Liquid manure from storages is normally agitated thoroughly before removal and hauled to the field for application using large tanker wagons or trucks. Liquid manure is either applied on the soil surface or incorporated shortly after application to control loss of volatile ammonia and release of odors. Incorporation is very effective at controlling runoff of manure nutrients and odor from land application if done within a few hours after application. An alternative application method is the use of 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 against the release of odors.

In larger operations, liquid manure may be pumped to nearby application sites and 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 seldom possible to use this method in heavily populated areas.

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Lagoons - Duck

Aerial view of Lagoon
Two-stage Lagoon System
(Source: Purdue University)
Lagoons are typically used only for laying hen production with flush-type pit systems, and in some duck production systems. Lagoons are different from liquid manure storages 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 lagoon is much larger and more expensive than a liquid manure storage with the same storage time, and should be much less concentrated, in terms of organic solids present.

Gravity Drain, Flat Bottom Gutter Reverse Hairpin Flat-Bottom Gutter
Gravity Drain, Flat Bottom Gutter Reverse Hairpin Flat-bottom Gutter
(Source: Purdue University) (Source: Purdue University)

Pit Recharge System
Recirculating Lagoon Water to Flush
Manure from a Gutter under a Slotted Floor
(Source: Purdue University)
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 from three days to three weeks. This is done by pulling a drain 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 one or more times a day or a "pit recharge" system that works basically like a toilet that is flushed every few days.

Treatment Volume
Single Stage Lagoon
(Source: Purdue University)
A portion of the lagoon contents must be left in the lagoon after contents are pumped to the land (a minimum treatment volume) to retain a large number of microbial organisms to treat the fresh 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 drops to the bottom of the lagoon, forcing the bottom layer, containing partially digested manure solids, to the top. This phenomenon can result in higher odor levels for a week or two around the lagoon.

Spray Irrigation
Irrigation of Lagoon
(Source: Purdue University)
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 stabilized. In a well-operated lagoon, effluent should have only about 20% as much nitrogen and about 30% to 40% as much phosphorous and potassium as raw manure, because of treatment and sedimentation of solids to the bottom of the lagoon. 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 very concentrated, it may be possible to haul the sludge off site or 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 normally be injected or otherwise incorporated as with liquid manure.

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Lagoons - Egg Wash Water

Since eggs from laying hen houses contain traces of manure on the shell, most states require that the water used to wash the eggs be collected and processed accordingly. Many laying hen operations collect this dilute wash-water in lagoon systems and apply the nutrients to croplands via irrigation systems (typically spray irrigation). Some producers treat this low-nutrient, wastewater using constructed wetlands or other systems prior to land application.

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Potential Environmental Impacts of Animal Feeding Operations

(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 groundwater, 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.

Table 1. Summary of U.S. Water Quality Impairment Survey

Total Quantity in U.S. Amount of Waters Surveyed Quantity Impaired by All Sources Quantity Impaired by Agriculture
3,662,255 miles
23% of total
840,402 miles
36% of surveyed
248,028 miles
59% of impaired
170,750 miles
Lakes, Ponds, and Reservoirs
41,600,000 acres
42% of total
17,400,000 acres
39% of surveyed
6,541,060 acres
31% of impaired
2,417,801 acres
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
Reference: National Water Quality Inventory: 1998 Report to Congress (EPA, 2000a). AFOs are a subset of the agriculture category. Summaries of impairment by other sources are not presented here.

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.)
Rank Rivers Lakes Estuaries
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:

Comprehensive Nutrient Management Planning

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Oxygen-Demanding Substances

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.

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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.

The Nitrogen Cycle

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)

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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).

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The Phosphorus Cycle

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.

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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

Disease Responsible Organism Symptoms
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
Hog Cholera Virus  
New Castle Virus  
Psittacosis Virus Pneumonia
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
Balantidiasis Balatidium coli  
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
References: USDA, 1992 (for diseases and responsible organisms). Symptom descriptions were obtained from various medical and public health service Internet websites. Pathogens in animal manure are a potential source of disease in humans and other animals. This list represents a sampling of diseases that may be transmittable to humans.

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).

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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 wastewaters, 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.

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Airborne Emissions from Animal Production Systems

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.

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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.

Liquid Manure Injected Directly into the SoilIn 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.

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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 Exit EPA 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.

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Environmental Impacts of Animal Feeding Operations Study Questions

Identify the definition that best fits the following terms:

  1. What are some of the positive environmental benefits of production agriculture?

    Improved soil quality
    Carbon repository
    Reduced storm runoff
    Ground water recharge
    All of the above


  2. USDA estimates that manure phosphorous exceeds crop needs in what percent of U.S. countries?

  3. What is the common name for the class of production agricultural plants that do not need commercial nitrogen fertilizer?
    N Converters

  4. If biodegradable organic matter is added to a stream, fish kills most often result from:
    Lack of oxygen
    Lack of visibility
    Build up of sludge deposits

  5. Most manure spills that enter streams result from:
    Pastured animals with stream access
    Rupture of manure storage
    Improper land application of manure
    Damage to manure transfer or irrigation pipes
    Feedlot runoff from animal area
    All of the above

  6. Nitrogen gas (N2) account for ___________ % of the atmosphere?

  7. Nitrogen in manure can take many chemical forms. Which of the following is NOT included?
    Nitrogen gas
    Organic nitrogen
    Catatonic nitrogen

  8. Which nutrient in runoff from agricultural land has been blamed for the hypoxia problem in the Gulf of Mexico?
    Soil erosion

  9. Which of the forms of nitrogen are volatile?

  10. High nitrate levels in drinking water can lead to the following serious condition in infants:

    "Green baby syndrome"


  11. The most important method of reducing phosphorous entering streams is:
    Placing riprap along edge of stream
    Preventing soil erosion
    Improving field drainage

  12. Which of the following is NOT a significant source of air emissions around a livestock or animal production operation?
    Feed processing
    Land application of manure
    Animal production lots and buildings
    Manure Storage

Score in Percentage:

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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 defined by EPA’s Guidance

Planning components of CNMP Issues addressed
A manure handling and storage plan
  1. Diversion of clean water
  2. Prevention of leakage storage plan
  3. Adequate storage
  4. Manure treatment
  5. Management of mortality
Land application plan
  1. Proper nutrient application rates to achieve a crop nutrient balance
  2. Selection of timing and application methods to limit risk of runoff
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
Reference is available from USDA/EPA Unified National Strategy for Animal Feeding Operations (PDF, 403KB)

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Poultry Production Study Questions

Identify the definition that best fits the following terms:

  1. Chickens are the most numerous birds in the world.

  2. Egg products are used for:
    Cake mixes
    Therapeutic vaccines
    All of the above

  3. What led broiler chicken production to expand beyond a seasonal, local market during the 1940s and 1950s?
    Advent of commercial poultry vaccines
    Mechanical ventilation systems
    Refrigerated trucking
    All of the above

  4. Most broiler chickens and turkeys are reared on raised wire flooring.

  5. Molting refers to:
    Process of making a pelleted diet with heat
    Process of reproductive rest where hens shed/regrow feathers
    Process of ventilation with electric or pneumatic fans

  6. The breeding chicken flock has moved to "black-out" housing to:
    Save on electrical costs
    Take advantage of the photosensitive nature of the bird for sexual maturation
    Prevent cannibalism

  7. Restricted feeding of broiler breeder birds is done to:
    Prevent obesity
    Save on feed costs
    Reduce labor costs

  8. The incubation period of a chicken egg is:
    18 days
    21 days
    28 days
    32 days

  9. A pullet is a:
    Male chicken of reproductive age
    Means of raising/lowering curtains in a naturally ventilated poultry house
    An immature hen

  10. Male turkey toms reach 40 pounds when marketed at 18 to 20 weeks of age.



  11. Poultry manure is routinely applied to fields through:
    Surface application

  12. This type of poultry routinely uses liquid-flush pit and lagoon systems:
    Broiler breeder

  13. These 2 factors have largely reduced time to market for broiler chickens from 12 weeks (1945) to 7 weeks (2002):
    Feeding and watering systems
    Nutrition and genetics
    Ventilation systems and vaccination programs

  14. To prevent the spread of disease, worker should always travel from:
    Housing for younger birds to older bird housing
    Housing for older birds to younger bird housing

  15. A laying hen reaches peak egg production:
    4 to 6 days after beginning to lay
    4 to 6 weeks after beginning to lay
    4 to 6 months after beginning to lay

Score in Percentage:

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