Iowa State University’s swine teaching farm started composting mortalities eight years ago in an effort to increase biosecurity practices. Swine farm manager Jay Lampe reports that move was positive.
“This process has changed our management style and lowered our biosecurity risks while providing a sustainable way of managing mortalities,” he says. “Composting has eliminated two potential sources of disease outbreaks — rendering and fuel trucks entering our property.”
The size of and cost to construct a composting facility varies according to available land, type of materials and size of mortalities. Iowa State’s facility has a full roof and eight bays; each is approximately 10 feet square with 4-foot-high concrete walls. This allows adequate space for all carcass sizes from the farm to be composted.
Tom Glanville, Iowa State agricultural and biosystems engineer, says the correct process of preparing and using a mortality composting facility is vital to its success. Start by placing a 12-inch layer of dry cover material, like sawdust, wood shavings or chopped corn stalks in the bottom of a compost bin. “Decaying carcasses will release excess moisture, so this absorptive base layer plays an important role in preventing release of excess liquid,” he notes.
You need to alternate layers of the cover material with additional carcasses until the bin or bay is filled. “The top layer should always be cover material,” Glanville says. “Realize that you might not be able to fill an entire bin in a short period of time, depending on your operation’s mortality rates and size of the moralities.”
Once filled, the compost must undergo a heating cycle of 60 to 90 days. Again, this varies based on the size of mortalities. After this cycle, the partially composted carcasses are moved from the primary bin to a secondary bin. “Moving the compost breaks up the materials, redistributes excess moisture and introduces a new oxygen supply,” Glanville notes. “By the end of another 60- to 90-day heating cycle, even large carcasses are normally reduced to a few large bones that are free of soft tissues which cause odors or attract insects and predators.”
Composting can continue through the winter months, but the facility layout plays a role. By having bins share a large amount of common wall area, it cuts down on the area exposed to the cold, reducing heat loss.
You can find more information about composting equipment, facilities, procedures, sizing and layout at extension.iastate.edu/store.
At the Iowa State swine farm, a nitrogen source (mortalities or manure) and a carbon source (typically corn stalks or woodchips) are the main materials used in composting. After the process is complete, the composted material is then applied on cropland. This adds organic matter and allows mortalities to be returned to the soil without odor or attracting insects or scavengers, Glanville says.