CFOs - Confined Feeding Operations

Impact of CFO Odor and Odor Setback Models

PDFImpact of CFO Odor and Odor Setback Models

Yingying Hong and Paul Ebner - Purdue Animal Sciences

In Duplin County, North Carolina, a full-scale wastewater treatment system (foreground) that replaced the swine lagoon.  

Odors can have varying effects on different people. There is a growing consensus that CFO odor, like other odors, at high concentrations can lead to physical reactions. In most cases, these reactions can lead to what are called “mood disturbances”, such as changes in mood, stress, etc. One recent study surveyed 101 adults living within 1.5 miles of at least one swine CFO over two weeks, and it showed a strong positive association between self-rated odor intensity and negative moods(Horton 2009). That is, the higher the odor intensity, the more likely individuals felt stress, anxiety, and other negative moods. Increases in self-reported disease symptoms, such as headache, wheezing, and nausea, were also sometimes observed in CFO neighbors when experiencing intense odor (O’Connor 2010). Two recent studies (Avery 2004; Wing 2013) have shown that intense odor can elicit some quantitative responses (e.g., some immune responses, elevated blood pressure). Many studies showed that the adverse physical symptoms were more prevalent in individuals who were highly concerned about CFO odor, indicating that stress could exacerbate physical symptoms (Donham 2010).

Currently, at the state level, CFOs in Indiana are not regulated based on odor. However, there are numerous tools available to individuals involved in CFO siting that are designed to aid in choosing sites where the CFO would have lowest impact on neighbors, specifically when it comes to odor. In many cases, community conflict could be significantly reduced by employing such tools at the onset of deciding where to site a CFO. The Purdue Agricultural Air Quality Laboratory has developed an odor setback model(Lim 2000), which incorporates facility size, types of animals, amount of manure generated, prevailing winds, and odor abatement practices, among other factors, to recommend setback distances and predict best locations for CFOs. This model is available to all Indiana counties. It is updated periodically, and can be accessed here: Livestock Odor Setback Model – Purdue University.

Another commonly used odor setback model is the Minnesota Odor From Feedlots Setback Estimation Tool (OFFSET model; Jacobson 2000). This model provides a range of setback distances for different “odor annoyance free frequencies”; defined as the percentages of time when neighbors will not experience an odor. In a previous study comparing five livestock setback estimation models, the setback distances recommended by the Purdue model were similar to the distances that provided 94% to 97% odor annoyance free frequency in the OFFSET model (Guo 2004).

More studies have confirmed that odor can lead to physical reactions in people living in proximity to CFOs. However, these symptoms and the community conflict they sometimes generate could be alleviated by using available tools that more scientifically identify sites where CFO odor will have the least impact on neighbors.


Avery RC, Wing S, Marshall SW, Schiffman SS. 2004. Odor from Industrial Hog Farming Operations and Mucosal Immune Function in Neighbors. Arch Environ Health. 59(2):101-8.

Donham KJ. 2010. Community and occupational health concerns in pork production: A review. J Anim Sci. 88:E102-11.

Guo H, Jacobson LD, Schmidt DR, Nicolai RE, Janni KA. 2004. Comparison of five models for setback distance determination from livestock sites. Canadian Biosystems Engineering. 46:17-25.

Horton RA, Wing S, Marshall SW, Brownley KA. 2009. Malodor as a Trigger of Stress and Negative Mood in Neighbors of Industrial Hog Operations. Am J Public Health. 99:S610-5.

Jacobson LD, Guo H, Schmidt DR, Nicolai RE, Zhu J, Janni K. 2000. Development of an odour setback determination tool for animal feedlots. ASAE Paper No. 004044. St. Joseph, MI: ASAE.

Lim TT, Heber AJ, Ni JQ, Grant R, Sutton AL. 2000. Odor impact distance guideline for swine production systems. Proceedings of the Water Environment Federation, Odors and VOC Emissions 2000. 16:773-788.

O'Connor AM, Auvermann B, Bickett-Weddle D, Kirkhorn S, Sargeant JM, Ramirez A, Von Essen SG. 2010. The Association between Proximity to Animal Feeding Operations and Community Health: A Systematic Review. PLoS One. 5(3):e9530.

Wing S, Avery Horton RC, Rose KM. 2013. Air Pollution from Industrial Swine Operations and Blood Pressure of Neighboring Residents. Environ Health Perspect. DOI:10.1289/ehp.1205109.​​​​​​

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