With rendering costs, biosecurity concerns and environmental regulations increasing, it's getting harder — and more expensive — to deal with carcasses on the farm. One alternative is composting — where naturally occurring bacteria (microbes) digest carcasses into a humus-like material called compost. The process works for manure, too.

Compost is a mixture of organic material that's been piled to undergo thermophilic (high heat, 120-160°F) decomposition. The heat generated by microbes known as thermophiles thrive on a diet of carbon (C) and nitrogen (N) in the right ratios, sterilizing pathogens and seeds.

Chris Augustin, North Dakota State University Extension specialist in Carrington, explains thermophilic bacteria break down the short organic chains of manure and carcasses, converting them into long, stable chains that are resistant to weathering and breakdown. The bacteria require oxygen, which is why bulking material is part of the compost equation.

He says the trick to composting is to maintain a C:N ratio between 20:1 and 40:1, 30:1 being ideal. Expect varying ratios of C:N as protein (low C source) and plant residues (high C source) intermix.

“Composting is more art than science,” Augustin says, as variables such as temperature, weather, carcass size and management make this process far from straightforward.

Step 1. Select the site

Site selection is important, Augustin says. Most large-animal compost piles are built in long, uncovered windrows, based on the carcass size and volume of material needed to cover them.

Piles should be constructed atop concrete or clay pads to avoid leaching or contaminating ground water. In fact, a permanent pad or base for composting piles makes it easier to work around in wet or dry weather.

Consider choosing a site with vegetation to reduce the environmental impact of leachate. Leachate is a flush of liquid, either from the decomposing carcass, or rain and snowmelt filtering through the pile. Harmful leachate can include chloride and ammonia nitrogen. A containment pond for leachate is ideal; Augustin recommends up to a 4% slope.

Follow good neighbor practices and avoid locating compost piles next to homes, main roads or picnic areas. Tom Glanville, Iowa State University (ISU) professor of ag and biosystems engineering, suggests locating compost sites 500 ft. away from homes and public roads, 200 ft. from public wells or visible bedrock outcrops, and 100 ft. from private wells or streams.

Step 2. Build the pile

Long, narrow windrows (base width 16-18 ft., about two loader widths) are easier to manage than broad-based piles. Though they will require more space, these windrows are easy to construct and maintain with typical farm equipment (Figure 1).

Pointed crowns and steep sides are recommended for wet climates to shed moisture, while a flat or concave top can be used in drier climates to accumulate moisture.

“It's important to have the right kind of envelope material under and around the carcasses,” Glanville says.

These materials can vary. Glanville field-tested corn silage, ground cornstalks and feedlot manure capped with ground hay. Base material should be about 2 ft. thick to absorb leachate. The heavier the carcass, the thicker the base should be.

Materials should allow air to pass through the pile, yet absorb leachate. Fine-textured material doesn't allow enough air to move through compost piles, which can leave large portions of carcasses intact. Conversely, overly coarse material can result in foul odors, flies and scavengers. Glanville had good success using a 2-in. grinder screen for envelope material.

“It can be too coarse, and it can be too tight. But there's a big wide friendly zone in between,” Glanville says.

For single or small carcasses, Glanville suggests a minimum pile width of 8-10 ft., and doesn't recommend placing more than two, full-sized carcasses back to back.

It's crucial to use enough material when composting and leave no part of the carcass exposed. A minimum 12-in. layer of co-compost (such as manure) should be placed around all sides of the carcass to discourage predators. This also helps heat the carcass and reduce odor.

Glanville recommends about 2 ft. of material over the top and sides of the carcass. He used 12 cu. yards of cover/base material for every 1,000 lbs. of carcass, equivalent to 1 ton of ground hay or straw, 1.4 tons of ground cornstalks or 3.2 tons of corn silage for large, uncovered and un-turned compost piles.

“It boils down to having about as thick of material underneath and over the top as the thickness of the animal itself,” he says.

Next Page: Managing the Pile