Producers use composting for livestock mortalities

PULLMAN, Wash. — Composting is one option for livestock producers to deal with animal mortalities.

“If you have livestock, at some point you are going it have mortalities,” said Lynne Carpenter-Boggs, soil scientist and professor at Washington State University. “That body needs to be dealt with very quickly to avoid odors or spreading disease.”

Composting is an aerobic decomposition of organic materials.

“During composting there’s a transformation of the organic raw materials biologically, chemically and physically to create compost that looks substantially different from the starting materials,” said Carpenter-Boggs during a webinar hosted by eOrganic.

Carbon and nitrogen are key to providing nutritious food for microorganisms to do the decomposition process.

“These microorganisms need sufficient oxygen and moisture to become very active,” Carpenter-Boggs said. “Once they’ve become active, they go into a feeding frenzy degrading the feedstocks.”

Carbon sources of feedstocks include wood chips, wood shavings, rejected feed, spoiled silage or haylage and straw used for bedding.

“Wood chips and straw are especially good materials for forming a base of compost,” Carpenter-Boggs said.

High nitrogen materials include the manure, separated solids, food waste and animal carcasses.

“Nitrogen feedstocks are important for increasing the heat, but they also can be potential sources of odor,” Carpenter-Boggs said.

“The ideal mixture is going to have 50% to 60% moisture, a carbon to nitrogen ratio of 30 to 1, a fairly neutral pH and sufficient air flow for aerobic activity,” she said.

“The temperature should heat up within a matter of days or at most two weeks, and it’s critical for the compost pile to get to 131 degrees,” she said. “This hot phase may last two to six months, and then gradually the temperature will decline as it goes through a longer, warm phase that lasts for up to 12 months.”

The hot temperature, Carpenter-Boggs said, is really important for the composting process.

“This is where management comes in by monitoring and documenting that there has been at least three consecutive days at 131 to 170 degrees,” she said.

“If it’s too cool, that means you don’t have effective composting and you’re not going to get a good reduction in pathogens,” she said. “If it’s too hot, there’s some risk of spontaneous combustion and you’ll get smoke or fire which is not very common, but you don’t want it to happen.”

On most operations at some point there will be turning or mixing of the compost pile.

“This will help blend the material and insure all of it has gone through good decomposition, and when you do that you’re incorporating more oxygen and bringing fresh feedstocks to the microorganisms,” Carpenter-Boggs said.

“You will likely see a temperature increase when you do the turning, but over time the amount of temperature increase is going to decline which shows the microbes have used up most of their foods.”

Composting livestock will likely look different for each farming operation depending on the available materials, livestock type, equipment and space.

Static piles can be used with lots of types of livestock, said Rachel Wieme, soil scientist and researcher at Washington State University.

“Lay down a large, thick base of high carbon and absorbent material — the key is at least 2 feet high,” she said. “We want it large enough so we can lay the carcass in the middle and still have plenty of space around the edges of the carcass.”

It is also important to have plenty of material covering the carcass, at least 2 feet thick.

“That material is acting as a biofilter by catching and absorbing odors, as well as insulating the pile to keep the temperature high,” Wieme said.

Composting in bins or stalls is an option that can work well for some livestock operations.

“The structure can allow for moisture management with a roof,” Wieme said. “With bins aeration is really important, and it can help speed up the composting process.”

Putting perforated pipes throughout the base material or adding a fan or blower to force air through the pile will add aeration to the process.

“The high heat of composting is effective for controlling against bacteria and viral pathogens,” Wieme said.

“Once you have your pile set up, microbes take over most of the work. However, you cannot completely walk away from it,” she said. “You need to check on your pile routinely to ensure biosafety.”

The end product of composting will be about half the mass and volume of the materials when it was started.

“While that process happens it could leave parts of the carcass exposed, and that needs to be remedied immediately,” Wieme said. “It can also happen from high winds or heavy rain.”

Any exposed part of the carcass will increase odors, and it can become a biosecurity issue, Wieme noted.

“It will attract pests such as hawks, eagles, coyotes, dogs or cats,” she said.

The compost pile is ready to be utilized as a fertilizer, Wieme said, when there are temperature drops and the materials do not significantly reheat when they are turned.

“It should have low or no odor, and it should be much darker in color from the buildup of humic acids,” she said.

Wieme highlighted some of the benefits of utilizing compost.

“It is a source of nutrients, it often provides a slight neutralization of soil pH and it is shown to increase soil moisture holding capacity through improvements in soil tilth and soil structure,” she said.

“Compost provides biotic inoculants, food and habitat for biology, so it is a great source of bringing more microbes into your soil,” she said. “It does act differently than other fertilizers because it is a slow release of fertility, so it will take a few years for half of the nutrients to be available for plants to use.”