Livestock manure is a valuable source of crop nutrients, but it can also come with pathogens that may cause livestock and people to become ill. The number and type of pathogens in manure vary based on animal species, feed, and animal health. There are many different types of pathogens in manure, so using multiple best management practices at once will give the best results.
Pathogens can infect humans directly through contact with manure or indirectly through contaminated water and food. Children, the elderly, and those with compromised immune systems are at the highest risk for infection.
Common manure pathogens include bacteria, protozoa, and viruses. These pathogens can cause fever, diarrhea, nausea, abdominal pain, vomiting, and in the worst case scenario, death. Over the years, there have been a number of disease outbreaks from manure exposure in the United States.
Common manure pathogens
|Escherichia coli (E. coli)
Disease outbreaks from manure exposure in the U.S.
|$ of people ill
|# of people deceased
|Source of outbreak
|Spinach contaminated by manure from a nearby cattle farm
|Washington County, NY
|Manure storage drained into shallow, unchlorinated well at fairgrounds
|Swimmers in lake contaminated with manure
|Swimmers in lake contaminated with manure
There are three main areas of focus where livestock producers can reduce pathogens:
In the animal
During manure collection and storage
During land application of manure
Stressed, unhealthy livestock are more likely to excrete pathogens than healthy animals. Therefore, keeping livestock healthy needs to be a priority to reduce the amount of pathogens in manure. Just because an animal appears healthy, does not necessarily mean that their manure will be pathogen-free. Some animals are carriers of disease without ever showing symptoms, themselves. Below are a few ways to keep livestock healthy:
Clean feed and water
Appropriate space allowance per animal
Sanitation and biosafety measures
Slotted floors or prompt manure removal from barn
Fly and vermin control
Another way to decrease pathogens in manure is through feed selection. Adding antimicrobials to feed will reduce the amount of pathogens in manure. Organic acids and yeast extracts added to feed have also been effective at lowering the amount of pathogenic bacteria in manure. In some cases, replacing a high-grain diet with a hay-based diet has reduced E. coli concentrations in cattle manure. Replacing finely-ground feed with coarsely-ground feed can reduce Salmonella content in swine manure. Livestock producers should talk to their veterinarian before drastically changing feed.
Using vegetative buffers near storage and areas of runoff will filter out pathogens before they reach a waterway. The effectiveness of a buffer strip depends on many factors, and the ideal buffer will have the following qualities:
Loam-textured soil for good infiltration
Soil with high organic matter and adsorption rate
Thick vegetation with deep, fibrous roots
No rill or gully erosion for even flow
At least 15 feet wide (MN law requires 16.5 ft along ditches, and 50 ft along lakes, rivers, and streams)
Time of year (buffers will be relatively ineffective during the winter and at snowmelt)
Follow Minnesota rules for manure stockpiles and open lots to help prevent pathogens from running off into waterways. Locate stockpiles on a flat, concrete or clay surface with at least two feet of separation from the seasonal high-water level. Catch basins downhill from the stockpile or open lot will intercept any manure that does run off. Clean water can be diverted from open lots and stockpiles by using berms, ditches, and gutters and downspouts. Be sure to fence livestock on pasture away from waterways to reduce the amount of manure directly entering water.
Storing manure under anaerobic (no oxygen) conditions, like deep pits below livestock housing, will also reduce pathogens. Though some bacteria can survive anaerobic conditions, most pathogens will be killed within 30 days. Using anaerobic digesters can accelerate the destruction of pathogens.
High temperatures combined with aeration also kills most pathogens. Composting is a good way to do this. A compost pile consists of organic material such as manure, bedding, and dead livestock. Temperatures within a compost pile can reach 150⁰F. We recommend two cycles of temperatures of at least 131⁰F to kill pathogens. Aeration and uniform heat distribution are mandatory for the breakdown of a compost pile into dark, soil-like material.
The following are a few other, more costly treatment options to reduce pathogens. Lime added to manure can reduce pathogens and odors, and when it is land-applied, it also reduces soil acidification. Ozone destroys bacteria, though the high organic matter content in manure can reduce its effectiveness. Ultraviolet (UV) light and Pasteurization at 158⁰F for 30 minutes are also effective at killing most pathogens. Chlorine disinfects drinking water but should not be applied directly to manure. Because manure has high organic matter content, it will be generally ineffective and can produce toxic and carcinogenic byproducts.
The main concern with pathogens at application is runoff and loss through tile drainage. People are at the greatest risk for pathogen infection when manure runoff reaches resources like waterways or food crops.
Pathogen concentrations decrease when exposed to UV light and drying. Since that naturally occurs when manure is surface applied, delaying manure incorporation will reduce pathogen numbers. However, waiting to incorporate manure can have adverse environmental effects as nitrogen is lost to the atmosphere and runoff risk is increased. Flies and vermin are also more likely to pick up and carry pathogens from manure that is left on the surface. Therefore, the recommended method is to incorporate manure soon after application.
To further reduce manure runoff, follow proper application methods to avoid over application. Test soil and manure for nutrient content to determine how much manure to apply. Calibrate equipment carefully for the intended rate. Avoid applying manure onto frozen ground where it cannot be incorporated.
Reducing pathogens in manure is important for livestock operations of all sizes, and the practices listed above will help do that. Before using each management practice, take into consideration the costs and benefits. Will these practices be economical? Will the social and environmental cost be too high if management action is not taken? All in all, reduction of pathogens at the agronomic level helps protect the health of people everywhere.
Reviewed in 2021