Getting Started with On-Farm Mortality Composting - gpvec

ON-FARM MORTALITY COMPOSTING RESEARCH AND EDUCATION PROJECT
A Project of the Washington State University BIOAg Program
www.mortcompost.info
Getting Started with On-Farm Mortality Composting
Composting can be a safe and effective method for disposing of on-farm mortalities. It allows
for immediate year-round disposal and on-farm nutrient recycling, as well as a marketable
product. When done correctly, carcass composting eliminates pathogens, does not contaminate
groundwater or attract pests, and creates a high quality soil amendment. There are several
important steps involved in a successful mortality composting operation.
Regulations
State requirements for reporting, testing of the final product, and volume produced vary
depending on the type and size of operation and use of the final product. Contact the Department
of Ecology or your local Health Department, or see the website www.mortcompost.info for more
information.
Equipment and Tools
The basic tools needed for a successful composting operation are:
Front-end or skid steer loader for moving materials and carcasses, and for building and
turning the piles.
Logbook to record dates and weights of carcasses in compost piles, temperatures, amount
and type of bulking materials, dates the piles are turned, and any other important
observations.
A probe-type thermometer with a 36’ stainless steel stem to monitor pile temperatures.
Location and Method
When choosing a location for the compost piles, drainage and accessibility are primary concerns.
The site needs to allow for leachate and water run-off management. Poor site drainage can cause
problems with water ponding and saturated materials, muddy working conditions, pathogens and
odors. A land slope of 2-6% is optimal. Ditches or berms can be used up-slope to divert storm
water around the piles, minimizing the total amount of leachate and run-off that must be
managed. The piles should be set back at least 300 feet from surface water and drinking water
wells. Avoid sites with lots of rocks, these get mixed in with the compost when it is turned.
Once a site is selected it is time to decide what kind of pile will work for your site and situation.
The two simplest options are windrows and static piles. A static pile is built for one mortality at
a time and remains separate for the entire composting process. A windrow is a long pile that can
be extended as needed.
Important Factors
A successful compost pile requires the right balance of moisture, Carbon to Nitrogen ratio,
particle size or porosity, and pile size.

The ideal moisture content is between 50% and 60%. The material should feel moist to the touch
but not wet. As a rule of thumb, if a handful of material does not feel moist to the touch and
crumbles after squeezing, it is too dry. If several drops of water can be squeezed from the
material by hand, it is too wet. If the material sticks together when it is squeezed and leaves a
drop or two of moisture on your hand, it is just right.
The ideal C:N ratio for a compost pile is 25:1 to 40:1. Materials that are too high in Nitrogen
and low in Carbon will lose gaseous ammonia or water soluble nitrates that can cause odor and
environmental issues. A mix that is too low in Nitrogen and high in Carbon will slow down the
composting process by limiting microbial growth. This is less of an issue with mortality
composting because the carcass is so high in Nitrogen, but it is still an important factor to
consider when mixing materials.
A particle size of 0.25 to 1 inch is optimum. It must be large enough to allow adequate air flow,
but small enough to prevent rapid drying or cooling of the pile. Larger particles do not absorb or
insulate as well and can cause problems with leaching, odors and pests. Woodchips and straw
can be useful to mix with denser materials to increase the porosity and oxygen availability, but
generally do not make very good composting materials by themselves.
The size of the pile will depend on the size and number of carcasses to be composted. A typical
pile will be 6 to 8 feet tall with a base width of approximately 1.5-2X the height. The piles
should be mounded to shed moisture in wetter climates. If low moisture is a concern, the piles
can be built with a depression on top to collect water. There must be enough space between
windrows or piles to maneuver equipment. When using windrows, carcasses can be added to the
end as needed but the location and date of each addition should be recorded.
Building the Piles
Before building the compost piles or windrows, the types and proportions of co-composting or
bulking materials must be selected. This will depend on the material available in the area and the
C:N and moisture content of these materials. Finished compost can be used for up to 50% of the
bulking material in a new pile. Using more than this will limit the nutrients available to the
microbes and slow down the composting process. Finished compost is especially helpful as a
‘blanket’ over the pile to reduce odors and insulate the pile in cold weather. See the website
www.mortcompost.info for a list of typical co-composting materials and their values.
Once the site has been selected and the materials gathered, it is time to build the pile.
Start with at a base of bulking material 2-3 ft deep. If high moisture or poor drainage is a
concern, a base of large wood chips or something similar under the bulking material will
help with aeration and drainage.
Place the carcass on top of the base of bulking material so that no part of the carcass is
less than 2 ft from any edge. Lance the rumen a few times to prevent bloating and speed
up decomposition. Then bury the carcass completely with at least another 2 ft of bulking
material. Again, make sure that all parts of the carcass are 2 ft or more from any edges.
This is very important! It is easy to underestimate the amount of material over the
carcass so it is a good idea to use a stick or some other method of measurement to double

check. The pile is likely to settle so watch it carefully for several days to make sure that
the carcass is adequately covered. Add more material if needed.
Record the date, number and size of carcasses, and bulking material used in the log book.
Monitoring the Piles
It is very important to monitor the piles closely, especially in the beginning, for odors, pests,
settling of materials, moisture and temperature.
Record temperatures and observations weekly in the log book.
As the microbes become active, the internal temperature of the pile will rise. In order to
kill any harmful bacteria or other pathogens, the internal temperature of the pile must
reach at least 131 o F for three consecutive days. As long as the pile stays hot the microbes
are still working. It is important to note that outside temperatures can also have an affect
on the internal temperature of the pile.
After several months of active composting, the pile can be turned to mix and aerate the
materials. Some large bones and hair may still be left at this point but the majority of the
soft tissues and small bones should be gone.
After turning, rebuild the pile and let it continue to compost. It is important to make sure
that the bones are adequately covered again after the pile is mixed so they do not attract
pests. Continue to monitor the pile and record weekly temperatures. The internal
temperatures should spike again as the microbes get back to work, and again internal
temperatures need to reach at least 131 o F for 3 days in a row to kill any pathogens.
Continue to monitor and mix the pile until the compost is finished.
The Finished Product
The final product should have no trace of tissues or unpleasant odor. Some of the bones may
still be left but should be brittle and easily broken. Large bones can be taken out and put into the
next compost pile if necessary. The finished compost should be brown or dark brown in color
and have a pleasant earthy odor. The texture should be crumbly, allowing air to penetrate but
holding moisture with out being saturated. Depending on materials and management, the entire
process can take anywhere from four months to over a year.
The compost can be stored in large piles on site until it is land applied, or transported off the
farm. If testing is required before distribution, the finished compost must be tested for:
Nutrients, Pathogen Levels, pH, and Stability. The tests must be done by a lab accredited by the
Washington State Department of Ecology.
More Information…
This is a very basic outline of what it takes to begin a successful on-farm carcass composting
operation. Keep in mind there is much, much more information available on anything from
bulking materials and pile construction, to troubleshooting and testing. There are many web
resources available from other states and universities, as well as books and videos. Starting a
successful on-farm mortality composting operation will take some research and planning but it
will be well worth the effort. Good luck!
ON-FARM MORTALITY COMPOSTING RESEARCH AND EDUCATION PROJECT
A Project of the Washington State University BIOAg Program
www.mortcompost.info