Paul Ebner
Animal Sciences
Purdue University
This publication is one title
in the Concentrated Animal Feeding Operations series.
To view the entire series,
visit
http://www.ansc.purdue.edu/CAFO/
|
CAFOs and Public Health:
Pathogens and Manure
Introduction
Concentrated animal feeding operations (CAFOs) can generate large quantities of manure, most of which is applied to fields as fertilizer. Plants are able to utilize many manure nutrients such as nitrogen and phosphorous; and in doing so, they limit the entry of these compounds into water resources where high concentrations can be harmful to both environmental and human health. Livestock manure can also contain disease causing microorganisms; and if manure is improperly stored or mishandled, these pathogens could pose a health hazard if they come in contact with water or raw foods. As such, there are concerns that the manure generated by CAFOs could result in infectious disease outbreaks in surrounding communities.
The aim of this fact sheet is to examine the fate of microbial pathogens in manure in an attempt to discern the actual health risks associated with the introduction of pathogens to the environment through livestock manure.
Manure and Microorganisms
Many of the organisms that cause infectious disease in humans, such as Salmonella, E. coli, and Cryptosporidium can be readily found in livestock manure. Often, these microorganisms are normal inhabitants of the intestinal tracts of animals and can replicate to high concentrations without doing any noticeable harm to the animal. In many cases, the organisms may be beneficial to the animal by aiding in the digestion and absorption of nutrients similar to the non-harmful microbes found in the intestinal tracts of humans. These intestinal microorganisms become part of manure when they are shed or excreted in the feces along with undigested food.
How Could Contamination Occur?
In most modern livestock operations, manure is collected and stored for variable amounts of time before being applied to pasture or cropland. Producers use different types of manure collection and storage systems, including pits (located underneath the buildings that house the animals), separate outbuildings, and man-made lagoons, as well as others (see Reference 1 for more detailed information on modern manure management).
Indiana regulations do not allow any direct (point source) discharge of manure or contaminated water into the waters of the state from manure storage facilities. In the past, the transfer of manure or effluent through pipes to lagoons has resulted in a high number of spills. The majority of new CAFOs in Indiana, however, do not use lagoon systems. Therefore, if collection and storage facilities are properly designed and maintained, there should be minimal risk of manure spillage, seepage, or overflow during this stage.
After a period of storage, producers then apply manure in varying stages of decomposition to fields as fertilizer. At this stage, non-point source introduction of manure into water is possible if the manure is improperly applied (e.g., applied to sloped land, eroding, or saturated soil, or at rates that would saturate the soils, etc.). Therefore, because the manure is less contained at the stage of land application, there is probably a greater risk of contamination of water resources (see Reference 2 for more detailed information).
Case Studies
It is often very difficult to definitively determine the origin of a microorganism involved in an infectious disease outbreak. This can be especially true for outbreaks involving raw foods or water. As such, while there have been cases where the responsible microorganisms were conclusively shown to come from livestock manure, they are rare.
One such outbreak occurred in Walkerton, Ontario, when heavy rains washed manure into well water thereby causing high concentrations of E. coli and Campylobacter to enter public drinking water. Over 2000 people were affected by the outbreak which included seven fatalities3. A similar outbreak involving E. coli and Campylobacter occurred in Washington County, New York, where manure run-off washed into an untreated well that serviced the fairgrounds4.
In the 1990s there were several outbreaks involving E. coli O157:H7 and apple cider. In most cases, it was believed that fallen apples were harvested from the ground of orchards that were either grazed by cows or were fertilized with cow manure. As a result, apple cider is now regularly pasteurized in the United States5.
There are also cases where livestock waste was implicated but not clearly shown to be the cause of an outbreak. The Cryptosporidium outbreak of Milwaukee, Wisconsin, which affected an estimated 403,000 people6,7, is probably the most famous. While this outbreak is often cited as a being caused by manure run-off from dairies, new evidence has shown that the origin of the causative agent is more uncertain7. Similarly, livestock waste was implicated in but not definitively shown to be responsible for a similar Cryptosporidium outbreak in Carrollton, Georgia, in 1989 affecting over 13,000 individuals4.
It is important to note that in those outbreaks where livestock manure was clearly shown to be the cause of contamination, the involved farms would not be considered CAFOs. Therefore, the risks are not exclusive to larger, confined operations but apply to animal manure as a whole.
What Can Be Done to Minimize the Risk?
Most of the human pathogens found in manure have adapted to live in the intestine; thus, they do not tend to survive for extended periods in soil or even manure. Therefore, the most effective tool in eliminating pathogens from manure, from both practical and economic standpoints, is time. If manure is allowed to sit undisturbed in storage or in soil, the concentration of pathogens will decrease with time as they die out or are overgrown by native microbes.
In Indiana, CAFO operators are required to produce and adhere to a manure management plan. In basic terms, a manure management plan describes the actions to be taken by the operator to ensure that the storage of manure, and its land application to cropland or pasture, will not result in over-fertilization and contamination of waterways. CAFO operators must outline how manure is collected and stored, how both manure and soil are regularly tested, and how much manure will be applied to fields, all the while, taking into account topography of their land, soil types, drainage courses, and nearby streams, ditches, or lakes8,9. While not specifically designed for pathogen reduction, measures that guard against over-fertilization, i.e., application at agronomic rates, should decrease the risk of pathogens entering water supplies by allowing time for large percentages of the pathogens to die out.
The following are recommended “best management practices” that CAFO operators can employ to further decrease the risks of manure pathogens entering water or food supplies 2,10.
1. Do not apply manure to wet or saturated soils.
2. Inject liquid manure or incorporate (mechanically mix into soil) solid manure on the day it is applied.
3. Apply manure only to frozen land if approved by the manure management plan, and only to land not prone to flooding, i.e., land with less than a 2% slope or land with proper erosion control practices in place.
4. Incorporate liquid manure in karst areas (areas with a limestone landscape, which are characterized by caves, long cracks, and underground streams).
5. Incorporate manure on non-erosive soils unless erosion control practices are used.
6. Use cover crops and other erosion control practices with erosion-prone land.
7. Ensure that storage sites are impeccably maintained and managed.
Conclusions
Because it is difficult to pinpoint the exact source of contamination in infectious disease outbreaks involving raw foods or water, it is difficult to determine the level of risk posed by pathogens in livestock manure. It does deserve further study, however, as livestock manure has been implicated, albeit rarely, in outbreaks in the past.
In Indiana, CAFO operators are required to produce and adhere to a manure management plan. While not specifically designed to reduce the risk of pathogens entering water supplies, the regulations designed to minimize contamination of water resources with nutrients such as nitrogen and phosphorus should also reduce contamination of water resources by pathogens by allowing the time needed for the organisms to be destroyed naturally. Because the consequences of manure mismanagement can be severe and affect large groups of people, CAFO operators should adopt best management practices (BMPs) that further reduce risks such as immediately incorporating manure into the soil, adopting various soil conservation practices, and diligently managing and maintaining storage sites.
References
1 Purdue University Cooperative Extension. 2007. Publications and articles on waste management. http://www.ansc.purdue.edu/dairy/waste/wastepub.htm.
2 Frankenburger JR. 2006. How pathogens from livestock can move to water resources. In: Pathogens in animal manure: should we be concerned? National Livestock and Poultry Environmental Learning Center Webcast. http://pasture.ecn.purdue.edu/ ~frankenb/pathogens-frankenberger/index.html.
3 Public Health Agency of Canada. 2000. Waterborne outbreak of gastroenteritis associated with contaminated municipal water supply, Walkerton, Ontario, May-June 2000. Canada Communicable Disease Report.
4 Gerba CP, Smith JE. 2005. Sources of pathogenic microorganisms and their fate during land application of wastes. J Environ Qual. 34:42-48.
5 Centers for Disease Control and Prevention. 1997. Outbreaks of Escherichia coli O157:H7 infection and Cryptosporidiosis associated with drinking unpasteurized apple cider—Connecticut and New York, October 1996. MMWR. 46:4-8.
6 Guan TY, Holley RA. 2003. Pathogen survival in swine manure environments and transmission of human enteric illness—a review. J Environ Qual. 32:383-392.
7 Eisenberg JN, Lei X, Hubbard AH, Brookhart MA, Colford JM Jr. 2005. The role of disease transmission and conferred immunity in outbreaks: analysis of the 1993 Cryptosporidium outbreak in Milwaukee, Wisconsin. American Journal of Epidemiology. 161(1):62-72.
8 Indiana Department of Environmental Management. 2007. Confined feeding operation. https://test.secure.in.gov/idem/agriculture/livestock/cfo/index.html.
9 Indiana Department of Environmental management. 2007. Manure management plan template. http://www.in.nrcs.usda.gov/technical/agronomy/590SamplePlan Template.doc.
10 Sutton A, Richert B, Jones D, Joern B. 1999. Best management practices (BMPs) to efficiently use swine manure as fertilizer. In: Indiana agriculture in transition. Purdue University Cooperative Extension.
|
