Horses and Manure

Horses are important for sport, work, pleasure, education, and therapy. In New Jersey, in addition to playing an important role in the state's economy, horse farms help to maintain open, green spaces that add to the scenic beauty of the state. Horses and the farms on which they live are often very valuable. To be good stewards of the land, horse farmers should manage their farms in a way to minimize the potential for negatively impacting the environment with horse manure.

This fact sheet gives an overview of horse manure production, quantity, and composition; the influence of diet on nutrient excretion; environmental benefits and impacts of horse manure; nutrient balance on horse farms; horse manure management; and regulatory compliance assistance. In this fact sheet, the term manure refers to both feces and urine.

Equine Nutrition

Basic knowledge about how equine nutrition and management influence manure production can lead to practices that reduce environmental pollution.

A horse will digest about 60% of most feedstuffs. This means that if a horse is fed 25 pounds of dry feed, 15 pounds will be digested and absorbed and 10 pounds will be excreted as feces. Digestibility will vary by feed and the horse's size, age, and productive status (work, sport, pleasure, breeding, pregnancy, lactation, retirement). Feeds that are higher in fiber such as hays and grasses will have a lower digestibility. Conversely, concentrate feeds that contain grains such as corn, oats, and/or barley, usually have a higher efficiency of digestion and less fecal excretion.

Nutrients in the feed are also of concern. Nitrogen (N) is a major component of amino acids, the "building blocks" of protein. Horses need protein for maintenance, growth, reproduction, lactation, and work. Phosphorus (P) is a macromineral needed for maintenance, growth, and other physiologic functions. Water is also essential for bodily functions. Water is lost from the body primarily in the excretion of feces and urine, respiratory loss, sweat, and in the case of lactating mares, in milk. Water intake affects the consistency of manure.

Horses should be fed a diet that is formulated to meet nutritional requirements, while avoiding excesses. All nutrients that are digested and absorbed are metabolized in the horse's body. Excess N derived from the amino acids comprising dietary protein is converted to urea in the liver and excreted in the urine. Undigested N is excreted in the feces. Therefore, overfeeding protein will increase the excretion of N. Similarly, overfeeding P will increase the excretion of P, most of which is excreted in the feces.

Horse owners should feed horses according to their nutritional needs. Specific recommendations for N (protein) and P intakes are given in the National Resource Council publication, Nutrient Requirements of Horses, 2007.

Manure Quantity and Composition

A 1,000-pound horse will defecate from 4 to 13 times each day, producing 35 to 50 pounds of manure daily—approximately 9.1 tons per year. Typically a ton of horse manure will contain 11 pounds of N, 2 pounds of P, and 8 pounds of potassium (K). To obtain more accurate numbers, manure should be tested for nutrient content (see Rutgers Cooperative Extension fact sheet FS935, Feed and Forage Testing Labs).

A horse kept in a stall will usually use about 10 to 20 pounds of bedding per day. This bedding should be replaced on a regular basis. Various types of bedding materials are used on farms (e.g., wood by-products such as shavings, chips, and sawdust; straw; or paper), so the composition of the manure-and-bedding mixture will vary from farm to farm. In general, manure plus bedding will have a volume of between 2 and 3 cubic feet per horse per day.

Environmental Impacts and Benefits

Environmental Benefits: When managed properly, manure can be a valuable resource on a farm. Manure can be a source of key nutrients for crop production (especially N and P). The organic matter present in manure can improve both soil quality and the water-holding capacity of the soil. However, most horse owners do not have enough land to use the amount of manure that is produced. Monitoring horse manure so that it does not cause environmental impacts is the goal of manure management.

Environmental Impact of Excessive Dietary Nutrients and Poor Manure Management: When not managed properly, horse manure can pollute groundwater or surface waters due to the N, P, and carbon (C; organic matter) content. These nutrients can reach waterways as surface runoff, or leachate, from the manure pile

Nitrogen excreted from horses is usually present as urea in the urine, which is quickly converted to ammonia (NH₃), or remains in association with organic matter in the feces. Ammonia (NH₃) can be volatilized into the atmosphere. If NH₃ or P or other nutrients from horse manure come into contact with surface waters (e.g., a lake or slow-moving stream), it can cause excessive nutrient enrichment, which can lead to the proliferation of algae and other aquatic plants, a process known as eutrophication. The subsequent death and decomposition of the algae may result in an environment that tolerates little life, plant or animal. (To learn more about eutrophication, visit the eXtension webpage or the U.S. Geological Survey webpage.

Nitrogen present in organic matter in the feces will be converted in the soil to NH₃ and then NO₃, which can be taken up by plants. Any NO₃ not taken up by plants can easily move through the soil and eventually leach into the groundwater and become a human health concern. Nitrate can also undergo the process of denitrification in the soil and be lost into the atmosphere as gaseous nitrogen (N₂), N₂O or nitrous oxide in particular, which is a global warming gas.

Phosphorus is also present in manure. When spread on the land it will not leach like N unless the soil matrix becomes overly saturated with the mineral. However, phosphorus will run off if applied at the wrong time of the year such as when soil erosion occurs. This can lead to contamination of surface waters where it may contribute to eutrophication.

When manure is not properly incorporated into the soil, organic matter present in manure (carbon, in addition to N and P) can be a concern when it runs off into surface waters. Eutrophication and additional oxygen depletion may occur due to the decomposition of the organic matter.

Pathogens and Vermin: Pathogens such as Escherichia coli, Salmonella spp., and Cryptosporidium parvum may be present in manure. However, the frequency of Salmonella and C. parvum is low in horse feces, and there have been no known outbreaks of E. coli infections in humans attributed to horses. Internal parasite infestations in horses may also result from improper horse manure management. Flies, rodents, dust, and odors may also be manure related concerns on horse farms. These problems can be minimized by proper design of housing and manure storage areas and careful attention when turning or moving manure piles.

Nutrient Balance of Horse Farms

When managed properly, nutrients from manure should be viewed as part of an overall cycle occurring on the farm (see figure). Nutrients enter the farm as feeds or fertilizer, are excreted as manure, and are subsequently spread on the soil for uptake by plants. The plants are then used as feed or sold from the farm.

Nutrient inputs include feed, animals, fertilizer, pasture forage growth, and bedding. Outputs are animals, milk, meat, manure, and crops. Nutrient recycling also occurs on the farm, from feed to horse to soil to plant and back to feed again if manure is used as fertilizer for pasture or hay crops. The optimal goal is for the farm to remain in balance between inputs and outputs with losses to soil, water, or air.

Soil can store nutrients from manure, assuming that the amount of manure applied to the soil is not excessive. When land application of manure is not managed properly, heavy rains can cause nutrient runoff to surface waters or leachate to groundwater. When land is over-manured and the ability of crops to take up nutrients is exceeded, these nutrients build up in the soil and pose a hazard in ground or surface water.

Ideally, farms will be able to maintain a balanced nutrient cycle and prevent wasteful loss of nutrients as pollution. According to the 2007 Equine Industry Survey, 42,500 horses are housed on 7,200 operations on 96,000 acres in the state of New Jersey. This is an average of 2.26 acres per horse and represents an acceptable stocking density. When managed properly, there should be adequate acreage for spreading manure on a farm with this stocking density while maintaining a balance of nutrients. Farms that stable or board horses on smaller acreages may have significantly less available land for spreading. These farms need to have ways of disposing excess manure off the farm.

Horse Manure Management

There should be a plan for manure removal. Manure should be removed from stalls or exercise lots on a regular basis. Manure disposal options include removal from the farm by haulers, direct land application, or composting with on-farm or off-farm use of compost.

Location and size of manure storage sites are important. Manure storage piles should be kept in a dry area not affected by flooding or storm runoff from paddocks, structures, or pastures. Do not store manure on a stream bank, near a wetland, or in an area that is close to the water table. Store manure on level ground if possible. Long-term storage structures, such as composting facilities or stack storage, should have adequate space. The storage structure should have a firm base and be covered to prevent runoff or leaching (tarp or roof). Appropriate conservation practices (buffers, filter strips, etc.) should be implemented to reduce surface loss of manure nutrients if the storage area is not covered.

When spreading, manure should be harrowed or otherwise incorporated into the soil. Nutrient losses from excessive manure spreading should be avoided, and manure should be applied based on a soil test and crop or pasture grass nutrient needs. Since manure is only slowly available after spreading, previous manure applications should be considered when applying manure to crops.

Spread manure only when the crops need nutrients, such as before or during rapid growth. Avoid spreading on frozen ground or near waterways. Remember that horse manure may contain internal parasite eggs or larvae. It is important not to spread horse manure on pastures where horses could become re-exposed to parasites, unless there is a good deworming program already in place.

When the composting of horse manure is done properly, internal parasites will be destroyed. The composted product can then be spread safely on pastures. Composting is the managed, accelerated decomposition of organic materials during which microorganisms such as bacteria and fungi break down the organic materials at elevated temperatures. Proper levels of moisture and air and the appropriate manure-and-bedding mixture are required to ensure proper decomposition. Turning the composting material helps to ensure that all parts of the manure are at elevated temperatures for suitable time periods. The final product will be freer of odors than horse manure and will have greater value as a soil amendment or fertilizer. The composting process will also reduce the total volume of manure for disposal. Location issues need to be addressed and are similar as discussed under manure storage.

Regulatory Compliance Assistance

Horse farms that pollute or discharge waste into New Jersey waters (regardless of the size of farm) may be regulated as Concentrated Animal Feeding Operations by the New Jersey Department of Environmental Protection (NJDEP). To assist New Jersey horse farmers, the State Department of Agriculture has developed an assessment and management process to help farmers manage horse manure. All livestock farmers in New Jersey are required to manage their manure in an environmentally friendly manner. Farms with seven or more animals units (one Animal Unit = 1,000 pounds) are required to develop an Animal Waste Management Plan describing how they manage manure on their farm. (For more information, please contact the New Jersey Department of Agriculture. Rutgers Cooperative Extension and the USDA Natural Resources Conservation Service are available to help develop plans for managing horse manure.

Conclusion

Horse owners need to manage horse manure to avoid pollution. Nutrient inputs, outputs, and losses all occur on a farm. Recycling of nutrients should be encouraged, and practices that contaminate surface waters or groundwater should be eliminated. Horse owners should remember that nutrients have value not only for feeding horses but also when present in manure where they can be a value or a detriment to the whole farm. It is the horse farmer's responsibility as a land steward to keep that cycle in balance.

Additional Information

For more information about horse manure management, check out the Rutgers Cooperative Extension website on Animal Waste Management. Our series of fact sheets on manure management address the regulatory control of horse manure management, the composition of manure, composting advice, and nutrient management. For additional help, you may contact your Cooperative Extension county office (see the Rutgers Cooperative Extension website).

Listed in the References section below are several publications and websites of interest. For example, the publication by Wheeler and Zajaczkowski (2002) is an excellent overview of horse manure management.

References

1. Agricultural Waste Management Field Handbook. 1992. National Engineering Handbook. USDA Natural Resources Conservation Service.
2. eXtension website on Animal Manure Management sponsored by Livestock and Poultry Environmental Learning Center: http://www.extension.org/animal_manure_management.
3. Foulk, D., R. Mickel, E. Chamberlain, M. Margentino, and M. Westendorf. 2004. Agricultural Management Practices for Commercial Equine Operations. Rutgers Cooperative Extension, New Jersey Agricultural Experiment Station Rutgers University. Bulletin Series #E296.
4. MWPS. 2005. Horse Facilities Handbook. MidWest Plan Service, Iowa State University, Ames, IA.
5. NJDA. 2007. New Jersey Equine Industry Survey. Rutgers Equine Science Center, New Jersey Agricultural Experiment Station, New Brunswick, NJ. http://esc.rutgers.edu.
6. NRC. 2007. Nutrient Requirements of Horses (6th rev. ed.). National Academy Press, Washington, DC. value
7. Wheeler, E. and J. S. Zajaczkowski. 2002. Horse Facilities 3: Horse manure stable management. Pennsylvania State University, State College, PA. http://www.abe.psu.edu/extension/factsheets/g/G97.pdf (PDF).

September 2013