Natural systems of all creatures, including humans, will purge pathogens or parasites through excrement. These pathogens and parasites are transferred to the compost pile with the manure, and may be present in the finished compost.
I don’t know of any manure that is 100% safe in every conceivable situation.
You must decide what level of risk is appropriate for you given your circumstances and that of your household. Be careful that finished manure is not used in a way that remaining pathogens could contaminate humans, pets, livestock or water sources.
If you are going to use manure in a home composting situation, ask your veterinarian (or a local veterinarian if you don’t have pets) what the risks to humans are for handling or ingesting that type of manure. This can change over time, so keep up with local news and ask the vet again on a periodic basis.
Always Avoid These Manures
Human feces. Human feces carry a high volume of disease-carrying pathogens. Do not compost human feces in any home composting system except a composting toilet that meets the legal requirements and licensing required for your location. If there are minimal or no legal requirements for your area, research systems very carefully, choose a safe system, make sure you have properly installed the unit and follow all manufacturer’s instructions for use.
Diseased animals. Do not compost manure of sick animals or animals that are on medication. Bacteria, viruses, or parasites causing the disease will likely be in the animal’s feces, as will medication not absorbed by the animal’s system.
Animals at risk of epidemic infection. Do not compost manure of any animals that are carrying an epidemic infection, or for which there is current risk for an epidemic. Avian and swine flu viruses are examples of disease that could be transferred to humans by contact with bird or poultry feces (or swine respiratory secretions) according to news reports. Your local vet and government health agencies should be able to advise you on current concerns in your area.
Cat feces, dog feces, and caged bird feces are covered in another article.
Consider these Factors that Increase Risk
When considering risk factors, think about exposure to finished compost as well as exposure to pathogens while the pile is decomposing. Many people assume the heat of a pile will kill bacteria, viruses, or pathogens. Remember that only the “sweet spot” in the center of the pile reaches a high temperature. Unless you turn a pile with meticulous care and precision, there will be materials in your pile that are never in the center and never reach a high temperature.
Pregnant women. If a woman who is pregnant or may become pregnant may come into contact with the compost pile or finished compost, take every possible precaution. Personally, I would not use any manure in this situation. Unborn fetuses can be permanently harmed by pathogens in pet feces. Do not take any chances.
Children. Children like to play in the dirt and their immune systems may not yet be fully developed. Take extra care if you have children in your household. Young kids eat dirt. Older kids slide into home plate or dive for the winning touchdown, often resulting in a face full of dirt.
Everyone gets dirty while working or playing outside and can subsequently put fingers in their mouth, or pick up food with dirty hands and put that in their mouth, or use their teeth to pull off a garden glove, or otherwise wind up with dirt (including finished compost) in their mouths and ingest it.
Weakened immune systems. Immune systems most at risk are those of the very young, the elderly, or immune systems impaired by disease.
Method of Composting. Lessen the human interaction with infected compost and you lessen the opportunity for transfer, so methods that limit your exposure should decrease the risks.
If you are composting in an open pile rather than in a compost bin, children and pets have immediate access to the pile and are more likely to come into contact with it. If you use an open pile or bin and turn the compost, you will have repeated exposure to any pathogens in it. If you use a tumbler, you will only come into contact with the compost when inputting and harvesting/spreading compost. If you use a soil ingestor, you will only come into contact while depositing materials into it, so this method would have the lowest risk provided it is not contaminating a water source.
Crops for Human Consumption. If finished compost will be used on vegetable or herb gardens, there is greater risk that it will end up being ingested by humans. Take extra care in your selection of inputs and make sure crops are adequately washed before being consumed.
Manure is a Common Input for Home Composting
Composting safely requires thought. Keep yourself informed, evaluate the risks in relation to your situation, and make wise choices.
Mary Tynes, Master Composter, www.mastercomposter.com
Image Credit: http://www.flickr.com/photos/niosh/2492033995/