Jump to main content.

Dairy Production

You will need Adobe Reader to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

Dairy production is an important part of American agriculture. Milk and other dairy products remain a staple in the diets of most Americans. In 2000, there were about 90,000 dairy farms in the United States. During the 1980s and 1990s, dairy production markedly shifted from the Midwest and Great Lakes regions to the West.

Modern dairy production is diverse with systems ranging from cows housed indoors year-round to cows maintained on pasture nearly year-round. Expansion to larger herd sizes has allowed producers to increase the efficiency of production and capitalize on economies of scale, but it has resulted in environmental challenges with larger numbers of cattle and more manure concentrated in smaller areas.

This module will look at dairy production as it has evolved in the U.S., the array of dairy products available, dairy production systems, milking systems, and typical manure handling systems in use today.

All photos are from M. Schutz, Purdue University unless otherwise noted.

Background of Dairy Production in the U.S.

The first cattle in the western hemisphere arrived with Christopher Columbus on his second voyage. Other cows began to arrive along with settlers from Europe and followed the pioneers westward. Until the mid 1850s, the dairy industry in America revolved around the family-owned dairy cow, with little sales of milk or other dairy products outside the family. The dairy industry began to change dramatically in the early 1900s, after a series of developments. Principles of bacteriology that led to improved milk quality and safety by Louis Pasteur with the process of pasteurization; development of breed associations that promoted the genetic selection of cows for their ability to produce milk; the Land Grant act of 1862 that established colleges of agriculture to educate farmers in the scientific principles of breeding, feeding, and management; the centrifugal separator that allowed milk fat to be removed and allowed the manufacture of more products; determination of milk fat content by the Babcock test (named for Professor S. M. Babcock of the University of Wisconsin); and tuberculin testing of dairy herds that eliminated milk as a source of tuberculosis all played a role in the growth of U.S. dairy production.

Milk Cows and Operations in Indiana

As the dairy industry grew in the first half of the Twentieth Century, the largest numbers of cows and dairy herds were located in the Great Lakes region of the U.S. This area was very suitable for pasturing cattle and for producing forages which could be stored as winter feed. It was also conveniently situated near the population centers of the U.S. at that time. The location of farms near the point of use was critical since milk is a highly perishable commodity and modern refrigeration and transportation systems were not yet available. Thus, milk was bottled at the farm or taken to a local creamery and delivered to stores and households daily. Cows and farms reached peak numbers in the 1940s, when rural electrification allowed for the rapid cooling and on farm bulk storage of milk and allowed it to be transported over longer distances to markets. This allowed dairy production to become more concentrated. Cow numbers and dairy farm numbers for Indiana, which is typical of states in the Great Lakes region are in Fig. 1.

Milk Cows and Milk per Cow in Indiana
The concentration of more cows on fewer farms was accompanied by dramatic increases in production per cow (Fig. 2), arising from improved genetic selection, feeds, health care, and management techniques. Better roads enhanced the ability to transport milk to processing plants, improvements in housing and environment to keep cows more comfortable, less competition for alternative land uses, and the ability to raise feed under irrigation has led to a shift in dairy production to Western states. California surpassed Wisconsin in milk produced in 1993 and in number of dairy cows in 1998.
Milk Cows and Milk per Cow in Indiana

Presently, there are about 9 million dairy cows on 900,000 farms in the U.S. California, Wisconsin, New York, Pennsylvania, and Idaho are the leading dairy producing states (Fig. 3). Production continues to increase in Idaho, New Mexico and California, while it is declining in most of the Midwest and Northeast. In the upper Midwest, dairy farms have been discontinuing production at the rate of more than three per day over the past five years.

2001 Milk Production Ranking
The tri-state region of Indiana, Michigan, and Ohio, however, appear to be maintaining or increasing cow numbers, as the industry reacts to relatively inexpensive feed costs and access to the high-demand markets for fluid milk in the Southeastern U.S. Continued growth of the industry is expected in the Eastern Corn Belt and in the High Plains, just east of the Rocky Mountains. External pressures on the dairy industry due to environmental concerns will limit its growth in some areas or force farms to relocate (Fig. 4).
Impacts on Dairy Production in Indiana

Top of Page

Dairy Products

Grocery Store's Dairy Case

A trip to the grocery store's dairy case shows the variety of products resulting from the milk. Fluid milk is available in several varieties - Skim Milk (0% fat), 1%, 2%, and Whole (approximately 3.5%). Raw milk is separated into skim milk and cream, and then re-blended to a standard fat content for each product. Because cows' milk averages more than 3.5% fat, the extra cream is used to make other liquid products like whipping cream, half and half, and eggnog or it is manufactured into butter or ice cream. Fluid milk in the U.S. is pasteurized (milk is pasteurized by rapidly heating it to 72 - 75 °C for 15 to 20 seconds, and then quickly cooling) to kill potentially harmful bacteria. Fluid milk is also homogenized (fat droplets are dispersed so they do not float to the top) and is fortified with vitamins A and D, which along with the absorbable calcium naturally in milk are needed for strong healthy bones and teeth. Over the most recent two decades, fluid milk consumption per capita has declined, and sales of low-fat milk have increased relative to whole milk. Recent innovative marketing of convenient single servings of milk and introduction of a wide variety of milk flavors have increased sales of individual servings.

Milk Bottling

Following the increased health consciousness of U.S. consumers in the late 1980s and 1990s, there was a period of decreased sales of butter, which is made by churning the cream portion of milk. However, sales have increased recently, as have sales of other high-fat products, such as premium ice cream and full-fat cheese. Cheese, which is made primarily from the protein (casein) portion of milk, also contains butterfat and currently accounts for a large percentage of dairy product demand and consumption. Per capita consumption of cheese consistently increases from year to year in the U.S. and is largely driven by demand for fast food and pizza. While demand for buttermilk (the portion of cream remaining after butter is churned out) and whey (the portion of milk remaining after cheese curd is removed) are negligible, the dried-powdered forms of these products are used as additives in the baking, candy, sport-drink, and animal feed industries. Whey powder also forms the basis for many brands of calf milk-replacers.

Health conscious consumers have also begun to purchase more yogurt relative to ice cream, and numerous low fat frozen deserts are available in grocery stores. Furthermore, milk is used directly in baked goods, candy and other ready to eat foods, like sauces and salad dressings.

Cheese Vat

In many states, the sales of meat from cull cows and bull calves that are raised as veal or dairy steers account for a significant portion of total beef production. Most cull cows, because they are older and produce less tender cuts of meat, are utilized for production of ground beef. Dairy veal and dairy steers are sold in similar markets and under identical USDA grading systems to more traditional beef breed steers. Byproducts of dairy beef production include leather, fertilizer, cosmetics, glue, and pharmaceuticals.

Top of Page

Dairy Production Systems

Black and white Holstein

Source: USDA - ARC

In the U.S., milk comes from breeds of cattle genetically selected for milk production. At one time in the U.S., cattle were selected simultaneously for beef and milk production. This is still the case in many parts of the world. The common dairy breeds in the U.S. today have been selected almost exclusively for milk production for many generations.

Black and white Holstein cows make up over 90% of the U.S. dairy herd. Some Holsteins are red and white, but, aside from color, indistinguishable from black and white Holsteins. The U.S. Holstein is well known around the world for her ability to produce large volumes of milk, butterfat and protein. She is a very profitable cow for farmers when large amounts of feed with high levels of grain are available. The U.S. Holstein is relatively new to North America, with the first imports of registered Holsteins arriving in the 1880s. However, the breed has dominated production in the U.S. since the end of World War II, and advances in artificial insemination have increased her popularity in breeding programs around the world largely owing to her advantage in production over all other breeds.

Jersey Cow

Source: USDA - ARC

The Jersey is the second most popular cow in the U.S. and makes up about 7% of the U.S. dairy herd. She is known for her smaller size (1000 lbs. for a mature Jersey cow versus 1500 lbs. for a mature Holstein cow), higher percentages of fat and protein in her milk, early maturity, and efficiency of milk production. Payment by milk processors to dairy producers based on the content of butterfat and protein in milk has increased the popularity of the Jersey, especially in markets where milk is manufactured into cheese. Other dairy breeds make up only around 2% of the dairy cattle population. These include:

More information about the breeds of dairy cattle. Exit EPA

A few other dairy breeds have become popular more recently. Dutch Belted, Danish Jersey, Normandy, Montbeliarde, Danish Red, British Friesian, and Norwegian Red have gained notoriety for their purported superiority under grazing management (pasture production systems). Many of these breeds have been developed in countries where grazing is widely practiced. Nevertheless, many U.S. dairy producers have good success grazing Holsteins and other traditional U.S. breeds of dairy cattle.

Until recently, very little crossbreeding was practiced in the U.S. Crossbreeding, which refers to mating cows to bulls of a different breed, is gaining in popularity for several reasons. Much of the genetic improvement in Holsteins has been for milk production alone, while other breeds have been selected for other traits like fertility, moderate size, disease resistance, and strength. Thus, crossbreeding allows the breeds to compliment each other's strengths. There is also some level of hybrid vigor expected in the progeny; that is, first generation crosses may be better than the average of the parents.

Grazing versus Intensive Dairy Production Systems

Cows on Pasture

In the United States, most milk is produced by cows raised in intensive production systems. These include tie stall barns, free stall barns, and open lots. The more intensively managed systems feed cows rations that are relatively high in concentrates and stored forages. Other cows are raised in pasture-based systems, which are the primary production system in several dairy producing countries in the world, such as New Zealand. Pasture-based systems often strive to optimize rather than maximize milk production while paying careful attention to controlling input costs. Some producers use a combination of the two systems, which is appealing in that it reduces costs, but still allows the feeding of concentrate to improve milk production levels.

Top of Page

Lifecycle Production Phases

Typical LIfe Cycle of a Cow

A cow typically remains in the dairy herd until about 5 years of age, although many cows are capable of remaining productive in the herd for 12 to 15 years. Following birth, the calf is usually removed from her dam after only a few hours. The newborn calf is fed milk or milk replacer until weaning at 6 to 8 weeks of age. The calf will then be raised until it reaches appropriate breeding weight at about 15 months of age. Heifers are then maintained and continue to grow through their gestation. They usually calve, or give birth, at about 24 months of age. However, they do not reach mature size until at least 4 years of age.

Newborn Calf

Normally cows begin to produce milk only after calving, but some heifers may be milked early to reduce stress and udder edema. Each period of production or lactation lasts for 12 to 14 months or longer and spans the time period from calving to dry-off, which is when milking is terminated about 60 days before the next anticipated calving. Thus, cows are bred while they are producing milk, usually beginning at about 60 days after calving to maintain a yearly calving schedule. Indeed, dairy producers attempt to get cows bred precisely during the time they are producing the most milk, which has negative implications for cow fertility. Following the 2-month dry period, the cow calves again and lactation cycle begins anew. Cows average about 2.5 lactations, although many remain productive considerably longer. Cows tend to survive longer in less-intensive pasture systems than when on concrete all of the time. The leading reasons cows leave the dairy herd are low production, infertility, mastitis (inflammation of the udder), and lameness.

Calves and Heifers

Valves are fed colostrum immediately after birth

Source: University of Wisconsin

Immediately after birth, the calf is fed 2 quarts of colostrum and at least another 2 quarts within 12 hours. The ability of the calf to directly absorb immunoglobulins from the cow's initial milk declines rapidly after the first 12 hours. Thus every effort is made to get the calf to consume colostrum early. Calves' navels are then dipped with iodine to prevent infection and the calf is moved to an individual pen or hutch as soon as it is dry. Choices for individual housing for calves include calf hutches, indoor crates, and indoor pens. Group pens allow too much nose-to-nose contact and permit disease to spread quickly for very young calves. Hutches provide very suitable ventilation for the calves and automated equipment can be used to simplify feeding calves in hutches. But indoor facilities are convenient for the calf feeders, especially in cold weather. Often indoor calf facilities are made of converted buildings, greenhouse barns, or coverall hoop barns.

Prior to weaning at 6 to 8 weeks, calves are vaccinated, dehorned, have extra teats removed, and male calves may be castrated to be raised as steers. Female calves are either raised by the dairy farm as replacement heifers, contract raised for the dairy farm by a heifer grower, or sold to other dairy farms. Male calves are mainly sold as veal calves or raised as steers, either by the farm or a buyer. A small number of bull calves may be raised for breeding stock and sold to local dairies as natural service bulls. A tiny percentage of bull calves from exceptionally good cows with registered pedigrees may be sold through contract to Artificial Insemination companies. Formerly, the image of the veal industry is that calves were kept in tiny crates in total darkness so they would remain anemic. The modern veal industry is more likely to be in more open facilities with excellent lighting and ventilation.

Protein Sources
Best Acceptable Inferior
Skim Milk Specially manufactured soy flour Unprocessed soy flour
Buttermilk Soy concentrate Meat solubles
Whole Whey Hydrolyzed fish protein Fish Flour
Delactosed whey   Distiller solubles
Casein   Brewer's yeast
Milk albumin   Oat flour
Whey protein concentrate   Wheat flour
Fat Sources
Lard Hydrogenated vegetable oils Liquid vegetable oils
Stabilized greases    

Aside from the very first days when calves are fed colostrum, they are fed discarded milk or milk replacer. The best protein sources for milk replacer are from dairy products. At the same time, the calf is offered water and calf starter feed, which it should be consuming readily prior to weaning it off of milk. Calves should be offered starter within the first week and should be getting adequate energy from the starter by weaning. Often calves are encouraged to eat the starter by addition of molasses. It is not necessary to feed hay to calves prior to weaning, but it is sometimes made available.

Protein Sources
  Grain Starters
1 2 3
Ingredients (air dry basis)  
Corn (cracked or coarse ground), % 50 30  
Ear Corn (coarse ground), %     50
Oats (rolled or crushed), % 22 18  
Barley (rolled or coarse ground), %   20 21
Wheat Bran, %   8  
Soybean Meal, % 20 16 21
Molasses, % 5 5 5
Dicalcium phosphate, % 0.5 0.5 0.5
Limestone, % 1.5 1.5 1.5
TM Salt and Vitamins, % 1 1 1
Composition (dry matter basis)  
Crude protein, % 18.1 18.0 18.4
TDN, % 80.0 78.8 78.0
ADF, % 7.0 6.9 9.1
Calcium, % 0.8 0.8 0.82
Phosphorus, % 0.48 0.56 0.47
Vitamin A, IU/lb 1000 1000 1000
Vitamin D, IU/lb 150 150 150
Vitamin E, IU/lb 11 11 11

At weaning, calves are moved to group housing. Forms of group housing include superhutches, drive-through freestall barns, drive-by freestall barns, and open housing on bedded pack. Some calves are weaned directly onto pasture. Normally, heifers are kept in these housing systems until they reach breeding age at 12 to 15 months. Feeds tend to include some calf starter, perhaps some other grain or corn silage; and excellent quality hay is offered.

Following breeding, heifers are maintained until moving to the dairy farm for calving. Facilities are often less extensive. Often heifers are raised in feedlots, or on pasture, although some heifers are also raised in freestall barns.

Back to Lifecycle Production Phases

Top of Page


Maternity Pens

For cows, the period from 60 days prior to calving until 40 days after calving is called the transition period, because cows make a transition to producing milk and consuming a higher energy ration. Heifers and dry cows are usually moved to a close-up dry area for close observation beginning at 3 weeks prior to calving. Usually the close-up dry cows are housed in freestalls, or on pasture or open lot. When calving appears imminent, cows are moved to individual maternity pens or an open calving area. Diligent efforts are made to keep these areas clean. Even cows raised on pasture are sometimes moved to pens for calving to allow close observation in case the delivery must be assisted, to keep the calf out of cold drafts, and to allow careful attention to the calf immediately after birth. Calving pens are usually bedded with lots of clean wheat or oat straw, although sand and sawdust are used too.

Some dairy producers prefer to keep cows on pasture. There are certainly advantages in reduced costs of feed harvest and storage, reduced cost for manure management and storage, improved foot health, and perhaps less disease when the cows are not as heavily concentrated in a limited area. These grazing systems often depend on the principles of managed intensive grazing to optimize grass and milk production. Some, but not all, grazers also practice seasonal calving to allow the cow's highest milk yield and energy demands to match with seasons of maximal grass production. Thus calving is planned for Spring in the Northeast and Midwest, and Fall in the far South. Due to less rainfall, little grazing is practiced west of the Great Plains. Grass is far and away the key component of diets on grazing dairies. Even stored feed may include excess grass from pastures that is ensiled and fed when grass is not available. Most grazing dairies supplement the grass with some level of ground corn or other concentrate feeds, and perhaps with some purchased alfalfa hay and/or corn silage. Often the grass is baled in round bales, wrapped in plastic, and stored as baleage.

Tie Stall Barn for Cows

In the Midwest and elsewhere it is common for small to medium-sized dairies to house cows in barns for most of the year, but to provide supplemental grazing during the summer. Even then, cows may only get a small portion of their forage from pasture, with most feed fed in the barn or a feedlot.

Traditionally, cows in the Midwest and Northeast were housed in tie-stall barns. Often cows were maintained in these barns and fed and milked right in their own stalls. While several of these barns are still in use, the inefficiency of labor and difficulty of milking have made new tie stall barns relatively uncommon.

Freestall Barn for Cows

The concept of providing cows with the opportunity to freely move from her stall to the feeding area was developed in Washington State in the mid 1950s. Freestall barns have become the mainstay of the dairy industry in recent years. Older freestalls were often constructed of wood and the stall was bedded with lots of straw. Even these older stalls can still be very useful today if plenty of bedding is provided to keep cows comfortable. Modern freestalls are more likely to be constructed of steel loops or dividers and bedded with sawdust or sand. The fact that sand provides little organic matter as food for bacteria, keeps cows dry, and helps cool cows in summer makes it the "gold standard" of bedding materials. Occasionally, freestalls are lined with rubber mattresses filled with ground tires, other cushion materials, or even water. Modern barns are constructed of wood or steel supports and rafters or trusses, steel roofing with an open ridge, and curtain sides that may be opened to maximize airflow in summer. Ventilation is usually assisted with fans. In some facilities, tunnel ventilation is used, in which air is mechanically drawn through the length of the building at rapid speed, which eliminates the dependence on wind speed needed for natural ventilation. To attain rapid air movement, the roof and sides are built solid with no air inlets. Greenhouse barns and other kinds of hoop structures are available to dairy producers for freestall barns. Their advantage is in reduced construction costs, although covering may need to be replaced as often as every 5 years. The additional light in these barns is an advantage for observing cattle, and the sun may be partially blocked out by covering with shade cloth in summer. Cow cooling systems, such as misters or sprinklers, are often present above feeding areas during hot weather. In the arid Southwestern states, newer dairy facilities are investing in state-of the art evaporative cooling systems to keep cows comfortable and productive. Supplemental cow cooling should be available any time the temperature exceeds 72 to 75 degrees.

Dry cows, during the period in which they are not lactating, are often housed in less expensive buildings. Because dry cows do not metabolize as much energy as lactating cows, they produce less heat, and so it is not as difficult to keep them cool in summer.

Back to Lifecycle Production Phases

Top of Page

Typical Herd

The typical mix of animals in a dairy herd for 100 milking cows is:

Milking herd:


Back to Lifecycle Production Phases

Top of Page

Feeding and Feed Storage

Typical Rations for Cows

Total Mixed Rations for Cows (Midwest Rations)



Typical rations fed to dairy cows in the Midwest often contain corn silage, alfalfa or grass silage, alfalfa hay, ground or high-moisture shelled corn, soybean meal, fuzzy whole cottonseed, and perhaps commodity feeds (corn gluten, distillers grains, soybean hulls, citrus pulp, candy bars, etc.). Proximity to crop processing plants and industries may dictate the availability of commodity feeds in different locales and some regions may have different feedstuffs. For example, short growing seasons may limit use of corn silage in far Northern climates and may be replaced by alfalfa silage in the ration. Cows are usually fed rations that are balanced for their milk production level or stage of lactation, which reflects the differences in energy and protein required for different amounts of milk produced. A cow produces the most milk immediately after the birth of her calf, but production drops off over the next several months. Usually, all of the feedstuffs are blended together in a mixer and fed as a Total Mixed Ration or TMR. Keeping every bite of feed a cow eats as uniform as possible helps to maintain a healthy population of bacteria in the cow's rumen (second stomach). It is the bacteria that digest the forages in the cows ration and allow her to consume and process foods that other animals and humans could not. Blending all feeds is difficult to accomplish in tie stalls, and is obviously not practiced with cows on pasture where cows eat only grass while on pasture and are fed grain at the time of milking.

Upright Concrete Stave Silos

Upright concrete stave silos

Feed storage and feeding systems account for a considerable number of buildings and structures on dairy farms. Dry hay may be stored in a hay loft, or second story, in the barn, in separate hay barns or stacked outside and covered with plastic. For many years, the primary storage structure for silage was an upright silo. Concrete stave silos and oxygen limiting silos, of which Harvestore™ is a familiar brand name, were popular storage structures for chopped and ensiled (fermented) corn, alfalfa, and grass. This method of storage was successful and cows readily ate well-fermented crops. However, the physical removal of silage from such storage was relatively slow and increasing herd sizes dictated more labor-efficient storage methods, such as silage bags and bunker silos, and silage stacks. These methods also preserve silage well, provided that the silage is adequately packed to eliminate oxygen that can hinder the fermentation process. Fermentation lowers the pH of the stored feed and preserves its feed value.

Feed Alley

Feed Alley

Commodity feeds are added to silage or hay to provide a complete and balanced ration. Commodity feeds are usually stored in a commodity barn that has several bays, one for each commodity. Commodity sheds are usually constructed to allow delivery of one semi-trailer of the commodity in each bay. Cows are usually fed at feed bunks in an outside lot, in a drive through feed alley in the barn, or at a drive-by feed alley, for cows housed in open lots.

Top of Page

Milking Parlors

Most Cows are Milked in a Milking Parlor

Cows are milked twice per day on most farms. However, 10% increased milk production can be obtained by milking the cows 3 times per day, and many dairy farms are beginning to do so. Some operations even milk a portion of their cows 4 times per day. Cows housed in tiestall barns are often milked in their stalls. A number of dairy farms, primarily those whose owners are members of religious denominations that do not utilize electricity, still milk cows by hand rather than with milking equipment. These are not common and usually involve only a few cows. The milk from such operations does not enter the fresh milk market and is utilized only for manufacturing purposes. Most cows milked in tiestall barns are either milked with bucket milkers or pipeline milking systems. Milking cows in tiestall barns is extremely labor intensive and requires much stooping and bending. The desire to reduce this type of labor has led to many types of milking parlor designs, in which the milker need not bend to be at the level of the cows udder.

Child Milking Cow

Source: Gennex, CRI

Some cows in the Midwest and Northeast are milked in Tie Stall Barns.

Walk-through Parlor

Walk-through Parlor

Walk-through or step-up parlors are often installed or retrofitted into existing tiestall barns as a cost effective way of alleviating the demands of the milking chore. In these parlors cows enter from the rear, step up onto an elevated platform for milking, and then exit forward through a headgate. Walk through parlors are inexpensive, but labor demands are still relatively high.

Step-up Parlor

Step-up Parlor

Herringbone Parlor

Herringbone Parlor
Source: Midwest Plan Service

One of the most popular types of parlors is the herringbone, so named because the cows enter and stand next to each other, but face away from the operator's pit at an angle. Milkers attach the milking clusters to the teats from the side of the cow, and to have better visual contact with the cow's udder while she is being milked. It is usually easier to keep the milker positioned properly beneath the cow's udder.

Parallel Parlors

Parallel Parlor
Source: Midwest Plan Service

Parallel parlors are similar to the herringbone parlors except that cows stand perpendicular to the operator pit and the cows are milked from the rear, between the cow's hind legs. Advantages are that the cows stand closer together so the worker has to walk less between cows that are being milked. Disadvantages are that the cow's tail is often in the way and it may be a long reach for some milkers to reach the cow's front teats.

Rotary Parlors

Rotary Parlor

Rotary parlors are gaining in popularity. Some older styles of rotary parlors were not very efficient or dependable. New ones, however, have proven to be a viable alternative for large dairy farms. With the rotary parlor, the platform on which the cows stand moves around, while the cleaners and milkers stand in one location. Milking cows is still a demanding task, however, because the cows come by so quickly that each task must be performed in about 10 to 12 seconds with no break between cows.

No matter what kind of parlor is used, there are some key components of milking procedures that are followed in each. Namely, the cow's teats must be thoroughly cleaned and dried, the milking equipment must be working properly and attached properly, and the teats must be disinfected with an approved teat dip following milking. This is to prevent possible spread of mastitis from cow to cow. Similarly, the milk must be handled properly after it leaves the cow. It must be cooled to under 45 degrees Fahrenheit within 2 hours of milking. Plate coolers are often more efficient at cooling milk than bulk tanks and are used on most farms. Bulk tanks manufactured after January 1, 2000 must be equipped with a recording thermometer so that the temperature history of the milk can be monitored. A sample of milk from each bulk tank accompanies the milk truck to the receiving plant. The milk undergoes a battery of tests to assure that it is safe and of high quality before it is accepted for processing. Dairy producers must meet specific requirements for bacteria counts and somatic cells (white blood cells) in milk; and they are paid a premium for high quality milk. No added water or antibiotic residues are allowed, under penalty of losing one's permit to sell milk.

Top of Page


Common Dairy Production Disorders

There are a number of common diseases and disorders that affect cattle at various stages of life (Fig. 1). Cows may experience a difficult birth, and death losses at birth may be as high as 5%, though these losses can be overcome by selecting bulls known for the calving ease of their offspring. Diarrhea, caused by any of several species of bacteria, and pneumonia are the leading cause of death loss in calves. Calves may also be afflicted with less harmful disorders like pink eye. In older heifers, the primary risks include pneumonia, injury, and bloat. Cows may be afflicted by any of a number of disorders that result in a loss of milk production. Mastitis (inflammation of the udder), lameness, milk fever (hypocalcemia), ketosis, reproductive disorders, and bacterial diarrhea are some of the more common ones. Vaccination programs are effective at controlling or decreasing the severity of many of these diseases.

Top of Page

Common Manure Handling Systems

Table 1. Manure Production per 200 Cows*
  Per Day (lb.) Per Year (LB)
Feces and Urine 24,100 8,800,000
Total Solids 3,360 1,230,000
Volatile Solids 2,800 1,020,000
Total N 126 46,000
Total P 26 9,610
Total K 812 23,600
*does not include wastewater and bedding
*estimates may increase with milk production

Cows differ considerably in the amount of manure they produce. Jerseys, for example, produce only 60% as much manure as Holsteins. With respect to many environmental rules, especially state regulations, however, no consideration is made for breed or body size. Composition of typical dairy manure is known (Table 1). Consideration must be given to the kind(s) of bedding used (Table 2) and the milking system (Table 3), both of which contribute to the amount of manure produced on a dairy farm.

Table 2. Bedding
Housing Type Chopped Straw Sawdust
Tiestall 0.8 0.1
Freestall 0.3 0.2
Loose Housing 1.1 ---
0.6 ft3 per cow is a good guide


Table 3. Wastewater
# Milking Cows gal/cow/d ft3
0 - 50 5 - 8 0.6 - 1.0
50 - 100 4 - 6 0.5 - 0.8
150 + 2 - 4 0.2 - 0.5
1 ft3 = 7.48 Gallons

Skidsteer loading a manure spreader

Skidsteer loading a manure spreader


A number of manure handling systems are utilized in dairy production. For tiestall barns, manure is collected in gutters behind the cows and removed from the barn as a solid material by a barn cleaner. Outside of the barn, the barn cleaner places the manure on a storage stack or directly into a manure spreader.

There are three types of manure handling systems used for freestall barns:

  1. Manual scraping,
  2. Flush systems, and
  3. Automatic alley scrapers.
Flush systems work very well

Flush systems work very well

Some freestall barns use slotted concrete floors above a pit, but these are quite rare in the U.S. With manual scrape systems, manure is scraped to the end of the barns by a skidsteer or mechanical loader with a scraping attachment. The manure is either stored temporarily in a solid stack, or loaded directly onto a manure spreader. Some barns are equipped with a freestall alleyway that is flushed with recycled wastewater to convey the manure to a storage pit or lagoon. Mechanical alley scrapers consist of a hinged v-shaped plough driven by a cable or chain. The plough is continuously or periodically dragged forward to draw manure to the end of an alley. When being pulled, the plough's blade splays across the entire alley between two curbs. After completing a pass, the chain or cable reverses direction and pulls the plough backward as the plough's blades fold together so as not to pull manure the opposite direction. Flush systems are comprised of a tank that delivers copious amounts of water to flush all manure off the alleys. Provided there is adequate slope along the channel and adequate water pressure from the tank, flush systems work very well. However, some concerns have been raised that a number of bacterial pathogens may be circulated through the barn by flush systems.

Storage containers

Storage Containers
Source: Al Sutton, Purdue University

Frequently manure from the freestall barn is stored temporarily in a storage pit and combined with more dilute waste from the milking parlor. Milking parlor waste often contains very little manure, but does have much residual milk from cleaning and may have various cleaning products as well. Manure from pits is agitated and then loaded onto a slurry wagon for application onto cropland, often with direct incorporation into the soil.

Effluent Drips Down for Collection

Effluent drips down for collection

Collection pits may also be used when solids are to be separated from the liquid portion of the manure. Solid separation can be mechanical, in which the liquid portion of the manure is squeezed though a screen. This provides a relatively dry solid that may be composted and perhaps even reused as a bedding material after drying. Sloped screen separators work by trickling the manure over a sloped screen so that the effluent drips through the screen with the solids sliding down for collection. Other mechanical separators draw an apron across the manure to force it across a screen. Concrete pit separators work by using a porous "weeping wall" in which the effluent is allowed to weep through the slots between boards or screens while the solids are retained. The solids then can then be removed as a semi-solid from the concrete pits. Composting is another option for solid manure management.

Settling Pond

Settling Pond

With sloping screen separators or other mechanical methods, the effluent may go into a settling pond to settle out even more solids before the effluent enters the lagoon. Many lagoons have been constructed with clay or compactible soil. In sandy or lighter soils, dairies must line the lagoons with compacted clay or synthetic liners.

New Technology

Recently, there has been much interest expressed in developing technology to utilize methane produced by anaerobic digestion of manure . As cost of the technology declines and pressure to manage manure and control odors on larger farm units increases, this technology will become more common. On some very large farms, these systems are used to generate electricity and hot water for the farm. Some are able to to sell electricity back into the grid through their local cooperatives. Cost of this technology remains too expensive for all but the largest producers at this time. Furthermore, anaerobic digestion should be viewed as a value-added process, but not as a solution to nutrient management difficulties, since nitrogen, phosphorus, and potassium remain in the effluent following digestion. Advantages appear to be in reduced energy costs, potentially reduced odors, and a more stable manure slurry.

Top of Page

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 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.

Table 1. Summary of U.S. Water Quality Impairment Survey
Total Quantity in US 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:


Top of Page

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.

Back to Environmental Impacts

Top of Page


The Nitrogen Cycle

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.


Back to Environmental Impacts

Top of Page


"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)

Back to Environmental Impacts

Top of Page


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).

Back to Environmental Impacts

Top of Page


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.

Back to Environmental Impacts

Top of Page


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).

Back to Environmental Impacts

Top of Page

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.

Back to Environmental Impacts

Top of Page

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.

Back to Environmental Impacts

Top of Page

Source of Airborne Emissions

Liquid Manure Injected Directly into the Soil

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.

Back to Airborne Emissions

Back to Environmental Impacts

Top of Page

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.

Back to Airborne Emissions

Back to Environmental Impacts

Top of Page

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:

Back to Environmental Impacts

Top of Page

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: USDA/EPA Unified National Strategy for Animal Feeding Operations (PDF) (34 pp, 404K)

Back to Environmental Impacts

Top of Page

Dairy Production Study Questions

Identify the definition that best fits the following terms:

  1. Heifer
    A female bovine that has not borne a calf
    An adult male bovine, normally used for breeding
    A really long time
    A type of silo unloader

  2. Holstein
    An older cow that is pregnant
    A full mug of beer
    A cow of the most common breed of dairy cattle
    A brown beef bull

  3. Freestall
    Complimentary room at the rural motel
    Feeding program for high producing cows
    A housing arrangement where cows can move freely between their feeding area and resting areas.
    A calf's hesitation when it is first removed from its hutch

  4. Leading Dairy Producing States
    Wisconsin, Texas, Indiana, North Carolina, Michigan
    California, Wisconsin, New York, Pennsylvania, Minnesota
    California, Idaho, Washington, New Mexico, Nevada
    Michigan, Ohio, Indiana, Illinois, California
    California, Wisconsin, New York, Pennsylvania, Indiana

  5. Pasteurization
    Process to make penicillin
    Removing cream from the skim milk
    Rapidly heating milk to 72 - 75 °C for 15 to 20 seconds, and then quickly cooling to slow growth of bacteria
    Managed intensive grazing of cows
    Boiling the milk to sterilize it

  6. Whey
    Juice that seeps from a silo when wheat silage is harvested and stored
    Portion of cream remaining after butter is made
    Oil used on clippers to trim hair from cows' udders
    Portion of milk remaining after cheese curd is removed
    Sarcastic response to someone who says "No way!"

  7. Guernsey
    A red and white to mostly red breed of cattle that are known for the yellow color of their milk.
    A famous garden seed company
    A type of portable shelter used where calves are kept when placed on pasture land
    A bracket for a milk pipeline
    A mostly black breed of cow with a belt white hair around its belly

  8. Dry Cow
    A martini made with milk and non-sweet vermouth
    A cow that is not producing milk prior to second or subsequent calving
    A cow with a very mildly humorous personality
    An indication of inadequate water intake
    The weight of a cow after the weight of water is discounted

  9. Calf Hutch
    A small, outdoor, individual housing unit for a calf
    A cabinet for calf medicine
    A disease of the calf's navel, sometimes called "navel ill"
    The most popular brand of calf milk replacer
    Calf Starsky's partner

  10. Estrus

    An indication that the cow is ready to be bred
    A type of grain fed to bulls
    The process of removing calves from the cow
    A hook used to hold rafters together
    An important religious holiday


  11. Bedding
    A cow blanket
    Sand, bare concrete, dirt
    Silage, soybean meal, feather meal
    Cotton seed, hay, tallow
    Sand, straw, newspaper, wood shavings

  12. Total Mixed Ration
    A feeding system where all feeds are blended together
    A feeding system where the cow is fed a single, but different, feed everyday
    A kind of cereal fed to cows
    A feeding system that allows the same feed to be fed to calves, heifers, and cows
    Limit feeding cows

  13. Rumen
    A chocolate brown breed of dairy cattle
    An additive in feed to prevent hardware disease
    A common antibiotic
    The largest compartment of a cow's "stomach"
    The act of renting a farm

  14. Parallel Parlor
    A long narrow room in the dairy farm office to receive sales persons
    A milking system in which cows stand side by side and milked from between the rear legs
    Two herringbone parlors set up side by side
    A completely automatic milking system
    The area just behind a cow's flank

  15. Mastitis
    Rigging in a ship's sail
    A breed of very large dogs
    Inflammation of the udder
    A swelling under the cow's jaw
    A young male calf

Score in Percentage:

Top of Page

This page is sponsored by EPA's Ag Center. Ag Center logo

Local Navigation

Jump to main content.