Dairy Production

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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.

• Background of Dairy Production in the U.S.
• Dairy Products
• Dairy Production Systems
• Lifecycle Production Phases
• Feeding and Feed Storage
• Milking Parlors
• Diseases
• Common Manure Handling Systems
• Potential Environmental Impacts
• Study Questions

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.

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. 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. 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. 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).

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Dairy Products

Dairy Products Fluid Milk Egg Nog Cheese Butter Yogurt Ice Cream Powdered Milk Whey Powder Butter Powder Meat Leather goods Fertilizers Cosmetics

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.

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.

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.

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Dairy Production Systems

(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.

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:

• Ayrshires - moderately large cows that are red and white to mahogany and white and are known for producing milk that is quite rich in butterfat and for the conformation of their udders;
• Brown Swiss - large brown cattle that are known for their docile manner, high milk protein to milk fat ratio, sound feet and legs, and purported resistance to heat stress in hot and humid regions;
• Guernseys - red and white to mostly red and are somewhat larger than Jerseys and are known for the yellow color of the butterfat in their milk, which is rich in Beta-Carotene; and
• Milking Shorthorns - a rugged breed of cattle that are red and white to mostly red, mostly white, or roan (speckled) and are known for milk that is well suited for cheese production and for their grazing ability.

More information about the breeds of dairy cattle.

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.

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.

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Lifecycle Production Phases

• Calves and Heifers
• Cows

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.

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Calves and Heifers

(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.

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.

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.

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Cows

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.

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.

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 wonderful 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.

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Feeding and Feed Storage

Total Mixed Rations for Cows Midwest Rations Corn silage Alfalfa/grass silage Alfalfa hay Corn Soybean meal Fuzzy whole cottonseed Commodity feeds (corn gluten, distillers grains, soybean hulls, citrus pulp, candy bars, etc.)

Mixer

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

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

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Milking Parlors

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.

Some cows in the Midwest and Northeast are milked in Tie Stall Barns. Hand Milking (Amish) Bucket Milkers Pipelines (Image Source: Genex, CRI)

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.

Walk-through Parlor
Step-up Parlor

Image Source: Midwest Plan Service
Herringbone Parlor

Image Source: Midwest Plan Service
Parallel Parlor

Rotary Parlor

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.

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Diseases

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.

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Common Manure Handling Systems

Table 2. Bedding   ft3/cow/day 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 Gal = 7.5 ft3

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

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.

(Source: Al Sutton, Purdue University)
Storage Containers

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

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.

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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 2 lists the leading pollutants impairing surface water quality in the U.S. Agricultural production is a potential source of most of these.

List of Contaminants in Animal Manure:

• Oxygen-Demanding Substances
• Nitrogen
• Ammonia
• Nitrate
• Phosphorus
• Pathogens
• Antibiotics, Pesticides, and Hormones
• Airborne Emissions from Animal Production Systems
• Study Questions

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

Nitrogen (N) is an essential nutrient required by all living organisms. It is ubiquitous in the environment, accounting for 78 percent of the atmosphere as elemental nitrogen (N₂). This form of nitrogen is inert and does not impact environmental quality since it is not bioavailable to most organisms and therefore has no fertilizer value. Nitrogen can form other compounds, however, which are bioavailable, mobile, and potentially harmful to the environment. The nitrogen cycle shows the various forms of nitrogen and the processes by which they are transformed and lost to the environment.

Nitrogen in manure is primarily in the form of organic nitrogen and ammonia nitrogen compounds. In its organic form, nitrogen is unavailable to plants. However, organic nitrogen can be transformed into ammonium (NH₄⁺) and nitrate (NO₃^-) forms, via microbial processes which are bioavailable and have fertilizer value. These forms can also produce negative environmental impacts when they are transported in the environment.

Ammonia

"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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Nitrate

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 (NO_x) 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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Phosphorus

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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Pathogens

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.

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.

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.

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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 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:

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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.

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Dairy Production Study Questions

Identify the definition that best fits the following terms:

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