Composting: Economical Alternative to Rendering

As rendering costs and biosecurity concerns increase, Iowa producers turn to composting death losses. In Ohio, producers are fine-tuning their techniques after six years of composting. When Dan Opheim stocked his new 2,000-head contract finishing barns last spring, he faced the tough decision of how to handle any mortalities. While dealing with dead pigs is not a pleasant thought, every producer must

As rendering costs and biosecurity concerns increase, Iowa producers turn to composting death losses. In Ohio, producers are fine-tuning their techniques after six years of composting.

When Dan Opheim stocked his new 2,000-head contract finishing barns last spring, he faced the tough decision of how to handle any mortalities.

While dealing with dead pigs is not a pleasant thought, every producer must be prepared to handle them. The Cylinder, IA, producer's plan included mortality composting as part of a Iowa Pork Industry Center demonstration project spearheaded by Iowa State University Extension livestock field specialist Dennis DeWitt and Extension ag engineer Kris Kohl.

In 2000, DeWitt enlisted pork producers to try composting as a cost-effective alternative to rendering services. In Iowa, much as in other states, rendering companies are charging more for their services. Some have closed.

“The cost of on-farm rendering service is rising to several hundreds of dollars a month,” DeWitt says. “Producers are seriously seeking a biologically and environmentally safe method of mortality disposal. Composting appears to fit the bill.”

As Opheim's finishers were being built, he considered buying a $4,000 incinerator or using a rendering service, which would cost at least $2,000/year.

Instead, Opheim built a composting unit in between his new contract barns for New Fashion Pork and a 500-head, open-front unit on another farm. That puts the composting unit about one-half mile from each barn site. This required Opheim to get an Iowa Department of Natural Resources (DNR) permit to compost mortalities.

Opheim purchased eighteen 10-ft.-long concrete pen dividers from a local ready-mix plant for $40 each. He constructed three 20 × 30-ft. bins, using soil to hold the partitions in place. Under the bins is a layer of 8 to 10 in. of cement truck washout (the leftovers from pouring cement), purchased for $400.

The total cost was $1,120 plus the one day Opheim spent constructing the bins.

To compost the dead hogs, Opheim uses the corn stover bedding from the open-front sow housing unit. He starts with a 1-ft. base of the bedding in the bin. The dead hog is laid on top of the bedding and then covered with more bedding. Subsequent mortalities, about 100 over six months, are added and covered with bedding. The demonstration project requires producers to keep a log of additions to the pile.

After eight weeks, Opheim uses a tractor with a front-end loader to turn the pile into the second bin. A third bin is used to complete the composting. In the fall, the finished compost is spread on fields in compliance with his nutrient management plan.

“I think producers will compost as they find how efficient this system is,” he says.

The composting pile allows him to immediately dispose of dead hogs and keep the rendering truck away from the farm.

Back to the Basics

DeWitt outlines the basic rules for composting in Iowa: producers must use a site with an all-weather surface (such as concrete or compacted gravel) and dispose of dead animals within 24 hours.

In addition, the Iowa DNR requires composting in a manner that prevents formation and release of runoff and leachate and controls odors, flies, rodents and other vermin.

The principle of composting is simple: the natural bacteria in the dead pig works to degrade the carcass while a carbon material absorbs the fluids, holds in odor and enhances the natural degradation process.

Any carbon source (sawdust, wood chips, bedding, corn stover, turkey or chicken litter) can be used.

The basic principle is to have a carbon (sawdust, etc.) to nitrogen (pig) ratio of 20:1.

The ratio should be adjusted depending on the consistency of the carbon material, DeWitt says.

“If the material is coarse, just add more depth to the pile,” he says.

Kohl gives a visual reference to use when making a compost pile. “Think of the pile as a chimney with air coming through the bottom and up to the top,” he says.

The amount of time needed to degrade carcasses depends on the age and size of the animal. Baby pigs can be totally composted in 30 days, but sows and boars may need 3 months or more.

Temperature Matters

Kohl and DeWitt suggest using a thermometer to record the daily temperature when beginning to compost. This will familiarize producers with the proper temperatures for efficient composting.

Temperatures inside a pile should reach about 140-160° F. Higher temperatures do not necessarily mean faster composting, Kohl stresses.

“People get excited when they reach high temperatures like 180 degrees, but those temperatures can also kill the bacteria that we want working in the pile,” he reminds. “On the flip side, temperatures below 120° F mean the pile may not be working.”

Producers should add more carbon when pile temperatures dip below 120° F.

Kohl describes a working compost pile as “fast, warm and non-odorous,” and a non-working pile as “slow, cold and stinky.”

Common Mistakes

Pork producers in Ohio have been composting their mortalities for six years. Roger Bender and Steve Foster, Ohio State University Extension agents, have helped producers become certified, a requirement in Ohio.

They outline common composting mistakes:

  • Not enough fresh sawdust on top of the compost pile. “We encourage producers to recycle the compost material, but we always recommend adding a foot of fresh sawdust on top as a biofilter,” Bender says.

  • No fence around the compost bins. Using wire fence panels to keep scavengers out is just good common sense, Bender says.

  • Not adding new mortalities immediately. Foster suggests assigning one person to be in charge of collecting the deads and properly placing them on the compost pile.

  • More precise management of a bin composting system may be necessary. Because bins have a limited amount of space, optimum management is needed to keep the pile active, therefore making room for the new mortalities.

  • And, don't forget convenience, Foster stresses. The pile must be located where it is easy to dispose of dead pigs.

“We have to find a labor-efficient way to handle the mortalities,” he says. “It needs to be a least-labor expense because the producer has already lost money on that pig when it died.”

Enhanced biosecurity is another key for producers to remember, Bender says.

“When the dead stock truck doesn't come around anymore, you greatly enhance biosecurity at the farm,” he says. “Those trucks violate every principal of biosecurity.”

Foster and Bender offer this analysis of the cost of mortality handling options.

If a producer has a 5,000 head/year finishing operation and 3% death loss, he will have about three 150-lb. hogs die each week.

If rendering services charge $50/trip, one stop a week costs $2,600 annually; two stops/week would cost $5,200.

Using the same operation, mortality percentage and an estimated incineration cost range from $0.80 to $1.75/lb., the cost to incinerate the mortalities would be $18,720 to $40,950/year.

Terry Knapke, Versailles, OH, set up a windrow composting pile (roughly 4-ft. deep and 35-ft. long) when he built two 960-head contract finishing barns.

The pile, which uses wood chips as the carbon source, is located next to the buildings. The wood chips are free from a local tree trimming service, Knapke says.

“I've used rendering services and buried animals, but this is easier and cheaper,” he says.

Size Matters

Opheim's composting unit is oversized, but that allows him to use a tractor loader to add mortalities, mix and spread the finished compost.

If producers choose to use a bin system, they can use a formula to estimate the space needed.

The National Pork Producers Council (NPPC) swine mortality composting module uses a formula to estimate the pounds of death loss/day, which is used to figure the space needed to compost.

Here's a synopsis of the formula:

  • Total the number of pigs born/year, number of sows, nursery and finishing pigs;

  • Multiply each number by the average weight of the animals and then by the percentage of death loss for each category or stage of production;

  • Take those four figures, add them together and divide by 365 for daily death loss.

  • Take that figure and multiply by 20. (NPPC figures 20 cu. ft./lb. of death loss).

  • Next, divide by 5, because the maximum bin height is 5 ft. This will equal the primary bin area.

  • Divide the primary bin area by the size (sq. ft.) proposed for each bin. This should provide the number of primary bins needed.

  • Round that number up to the nearest whole number and estimate a minimum of one secondary bin for two primary bins. Then add another bin for storage of carbon material.

NPPC estimates the cost of building a structure to compost mortalities at $1,500 to $2,000/bin.

Basic Principles for Composting Mortalities

Here are several basic principles to remember when composting swine mortalities.

Each state has rules on composting sites. Some states, like Minnesota, require a roofed structure. Other states only require that composting is done on an all-weather surface, for example, concrete or packed gravel.

Another important thing to remember in using an outdoor pile is proper maintenance. The top of the pile should be groomed regularly to avoid depressions that could collect rainwater. Extra water could slow the bacteria process, causing odors and drawing flies, reminds Roger Bender, Ohio State University Extension agent.

An unused, open-front barn may be perfect for composting. The roof prevents too much moisture (rain or snow) from entering the pile, the building allows for storage of extra carbon material, and the floor is slopped appropriately for drainage.

The basic layout of a compost pile is the same whether a bin is used or a windrow system is implemented. A 1-ft. or thicker layer of carbon material should be spread, then the dead animal placed on top, then another layer of carbon. The carcasses should not touch and should be placed in the pile before they start to freeze or decay.

Moisture content is a big key to getting a compost pile started. The appropriate range is 50-60%.

Placement of deads in the pile should be routine for workers. The biosecurity procedures should be the same for the compost pile as they are for the farm. One worker should have composting responsibilities, preferably at the end of the work day.

Any carbon material will work in a composting pile, reminds Dennis DeWitt, Iowa State University Extension. A material with multiple particle sizes works better than all coarse or all fine material.

Compost material that has been partially used will work faster than new material because it is already inoculated with bacteria.

Location of the composting pile is important. Producers should consider aesthetics and landscaping, provide limited or appealing view for neighbors or passing motorists when siting a pile. In addition, maintaining biosecurity precautions is a must, DeWitt reminds.

For more information on composting or to acquire the NPPC swine mortality composting module, contact NPPC at (515) 223-2600, visit or contact your state pork producers association office. The cost is $15.

Consult your state department of agriculture or department of natural resources for regulations governing composting of swine mortalities.

Several Web sites offer a wealth of information on composting: