Increased public concern for the environment and resulting stricter regulations governing the disposal of dead pigs presents a new challenge for the hog industry. The volume of dead pigs produced annually is daunting. A 1000 sow farrow-to-finish farm with a mortality of 7%, 10%, 5%, 1%, and 1% in the sow, neonatal, nursery, growing, and finishing herd respectively, will produce in one year over 40,000 pounds of dead pigs. In the past, these pigs have typically been either buried, incinerated, or taken for rendering. Unfortunately, each of these options now is less acceptable or unavailable. Buried animals can contaminate ground water and smoke from burning animals contaminates the air. Also, with the closure of many rendering plants, fewer hog operations have that option. The industry's challenge is to find inexpensive, environmentally-friendly alternatives for the disposal of dead pigs. This article will review the methods for dead pig disposal being developed, and those that warrant investigation. Two techniques developed by the poultry industry - composting and fermentation - have great potential for the swine industry. However, dead pig disposal is regulated and State authorities must first approve alternative techniques before they can be implemented in the field.

On-farm Procedures

Most pig carcasses are disposed of on-farm. The methods used include trench burial, disposal pit, burning, or the more recent opportunity--composting. The major advantage of an on-farm system is its biosecurity. On-farm systems do not require outside collection-trucks to visit the farm nor do farm trucks have to risk contamination when visiting a rendering plant or central collection site.

Composting

The poultry industry, which has had increasing difficulty in disposing of its dead birds, has found an alternative in composting. Composting uses waste products such as dead pigs, straw, and poultry litter and converts them into an odorless, inoffensive, generally pathogenfree product that can be used as a soil amendment or organic fertilizer. The process of composting carcasses is the same as that used to compost garden waste. A succession of mesophilic and thermophilic microorganisms including bacteria, fungi, and actinomycetes feed on the organic substrates to produce carbon dioxide, water, minerals, and a stabilized organic matter called humus. The speed and efficiency of this aerobic process depends on the temperature, nutrients, moisture, availability of oxygen, and particle size.

Temperature

Because of the diversity of temperaturesensitive organisms in a pile, some decomposition occurs at virtually any temperature. However, the optimum temperature for microbial activity is less than 550C. In Missouri, decomposition of pig carcasses slowed considerably in winter but increased in the spring when temperatures rose. In North Carolina, our compost piles have consistently reached temperatures over 550C, killing most of the Salmonella, and all of the Erysipelas, in broth cultures placed throughout the pile. Poultry compost piles routinely attain 700C. The temperature can be controlled by adjusting aeration and moisture and covering the pile with an insulating layer of the carbon source, e.g., straw, each time pigs are added to the pile.

Nutrients

Composting microorganisms need appropriate nutrients to work effectively. The most important are carbon and nitrogen. Phosphorous, sulfur, calcium, and trace quantities of other nutrients are required for cell growth. A carbon/nitrogen ratio between 20:1 and 35:1 is optimal. Above that range, decomposition slows. Below a ratio of 15:1, nitrogen is lost as ammonia, that reduces the value of the humus and creates an odor problem. Getting this ratio right is a major factor in successful composting. The recipe we have successfully used is 100 pounds of dead pigs, 150 pounds of turkey litter, and 10 pounds of wheat straw.

Moisture

Since water is essential for nutrient solubilization and cell protoplasm, a moisture content below 20% can severely inhibit the process. Too much water will block air movement causing the pile to become anaerobic. The optimum moisture level is 45-55%. We have achieved this level by adding four gallons of water to the recipe above.

Oxygen

Decomposition in the compost pile is fastest when it is all aerobic. In reality, aerobic conditions probably exist only at the periphery of the 6X4X5 ft piles we construct. Accordingly, decomposition is slower. Commercial composting operations for municipal waste can mechanically aerate their piles, for example, by periodically turning the pile, inserting perforated tubes, dropping the piles from floor-to-floor or pumping air through them. Too much aeration can dehydrate the pile and waste heat. Consequently, the piles may not attain the temperature to operate successfully or to kill the pathogens. In practice, the piles are turned 2-3 days after temperatures peak. This aerates the piles and restarts decomposition. Emulating the success of composting dead birds we have found that it is sufficient to turn the pile three times.

Particle Size

The smaller the particle size of the compost the greater the surface area available on which microorganisms can work. However, some material must be large enough to provide structural support and to trap the oxygen for aerobic digestion. In practice, pig carcasses of less than 30 pounds need not be cut open and the straw that we have used provides carbon, structural support and the aeration necessary. Dennis Murphy has demonstrated that by cutting into their thorax, abdomen, and muscles it is possible to compost pigs weighing up to 300 pounds.

The location, construction, operation, and precautions for composting dead pigs is similar to that required for poultry as detailed in the publication "Composting Poultry Mortality in North Carolina" available from the North Carolina Cooperative Extension Service. We are now tailoring those requirements to the swine industry.

As Feed for Animals

In deference to the mink industry the state of Minnesota specifically allows feeding carcasses to fur animals. The hazard of feeding dead pigs is well known by any farmer who has lost dogs and cats by allowing them access to pigs that died of Aujeszky's disease. However, opportunities for feeding carcasses to animals, other than fur bearing ones, exist. One 2000 sow hog farmer in Pasco county Florida is profitably feeding processed dead hogs and poultry to alligators that are slaughtered for their meat and hides. Also, a hog farm in Singapore used to feed all its dead pigs to crocodiles that were slaughtered for the local leather industry.

Off-farm Procedures

The two main opportunities for carcass disposal off-farm are taking them to a landfill or a rendering facility. Landfill opportunities are decreasing as municipal authorities refuse carcasses although they are permitted to take them. Rendering has been, and will continue to be, the best means for converting carcasses into a valued, biologically safe, protein by-product. Unfortunately, fewer rendering facilities are operating, due to depressed world prices for fat, protein, and hides. Thus, transporting carcasses can be prohibitively expensive. Some counties have designated sites for the central pickup of carcasses, but any off-farm facility is a biosecurity risk. Exciting opportunities are developing in the poultry industry that will enable carcasses to be stored on-farm until enough accumulate to make a trip to the renderer feasible. These techniques include freezing, fermentation, or acid preservation. Another opportunity that can be operated either on- or off-farm is extrusion. Lastly, flash dehydration and fluidized-bed drying are two emerging technologies that could be used to recycle dead pigs.

Central Pickup

Central pickup, and delivery to a rendering plant, is an environmentally sound and efficient method for recycling pig and poultry carcasses. Because the central site is visited by many producers, biosecurity is critical and strict guidelines must be established. Construction costs vary dependent on the work required at the site. Price received for the carcasses also can vary considerably. Greene county in North Carolina profitably operates a site that accepts both poultry and livestock.

Freezing

Freezing was one of the first methods tried to extend the on-farm storage time for poultry carcasses before rendering. Recently, a large poultry integrator has developed a purpose built freezer for holding dead broilers. They plan to use it extensively for preserving carcasses before taking them to a renderer. Each freezer will hold about one ton of dead broilers. The company estimates the electricity costs at about $1.20 per day or $0.01 per pound of dead bird assuming $0.08 per kilowatt hour. These units may be generally available soon for about $2000.

Fermentation

First proposed in 1984, fermentation provides a system that can store chicken and turkey carcasses for at least 25 weeks and produce a silage end product that is pathogen free and nutrient rich. Sanders (1990) recently conducted an extensive review on the subject. Fermented poultry offal, fed at up to 20% of growing-finishing pigs' ration, does not depress gains or increase feed-to-gain ratios. Unfortunately, no one has documented feeding hogs the silage from fermented whole birds or pigs. The bacteriocidal and viricidal activity of fermentation depends on the pH and temperature attained. Viruses labile to low pH do not survive fermentation; inactivation occurring rapidly at 400C, but more slowly at lower temperatures. Most importantly, in fermented silage, Aujeszky's Disease Virus (ADV) is rapidly inactivated at 200C to 300C but survives two days at 100C and nine days at 50C. The optimum temperature for fermentation is about 350C but silage temperature approximates ambient temperatures, indicating that ADV may not be inactivated in colder regions. Fermentation with Lactobacillus acidophilus destroys many bacteria including Salmonella ssp, Salmonella typhimurium, and Clostridium botulin type E.

Fermentation is an anaerobic process that can proceed in any size noncorrosive container provided it is sealed and vented for carbon dioxide, 55 gallon drums are commonly used. Daily, carcasses are ground to 1" or smaller particles, mixed with a fermentable carbohydrate (CHO) source and culture inoculant and then added to the fermentation container. The grinding aids in homogenizing the ingredients. For lactic fermentation, lactose, glucose, sucrose, whey, whey permeate, and molasses are all suitable as a CHO source. Condensed brewers solubles is a particularly appropriate CHO source because it is a fermentation byproduct and silage pH rapidly drops when it is used. Under optimal conditions the pH of fresh carcasses is reduced from 6.5 to less than 4.5 within 48 hours. A properly prepared silage is semi-solid, will last for months and is readily accepted for rendering. Other potential uses for fermented carcasses is in mink or fox feed, extruded aquaculture feeds, and ruminant silage. A pH greater than the optimum 4.3-4.5 can result in a secondary fermentation that spoils the silage. Recently, the recipe was varied to include a proteolytic yeast (Hansenula montevideo), instead of Lactobacillus, for the inoculant and an out-dated, non-diet, soft drink syrup for the CHO source. The result was satisfactory.

Acid-Preservation

Ground, split, or punctured dead broilers can be preserved on-farm at least one month in a 3.4% sulfuric acid solution at a cost of $0.10 per pound of carcass. When this acid-preserved product was rendered it has the same nutritive value as regular poultry-byproduct meal. Acid preservation of pigs has not been tried but may eventually be an inexpensive on-farm method for storing carcasses. The safe handling of sulfuric acid stock solution is a primary concern.

Extrusion

Extrusion is not a new technique for the food industry. It has been used to process human food for more than 50 years and it is the foundation of the pet food industry, producing 13 billion pounds of product with a market value of $8 billion annually. If extrusion is used to process carcasses it will most likely be done centrally because of capital costs. However, if it can also be used to extrude full-fat soybeans and creep feed, individual farmers may be able to justify the cost.

Material is fed into a raw material bin, then to a mixer, and finally into the extruder which works by using friction to create heat, shear, and pressure. In the extruder, a screw (or screws) forces the material through a series of baffles where temperatures of 115-1550C and pressures of 20-40 atmospheres develop for about 30 seconds. The sudden decrease in pressure as the product leaves the extruder causes it to expand and lose 12-15% of its moisture. The food industry mostly uses single screws because they are about 50% cheaper. However, double screw systems can better cope with the high moisture ingredients and therefore would be more appropriate for dead pig disposal.

High quality feed products have been manufactured from extruded whole chicken mortalities, poultry offal and feathers, and hatchery waste. The extrusion process is particularly adept at inactivating bacteria, molds, and viruses.

Fluidized-Bed Drying and Flash Dehydration

Fluidized-bed roasting/drying technology was developed a few years ago for roasting full-fat soybeans. A centrifugal fan blows air over a natural gas or propane burner, heating the air to 3000F. Raw material entering the roaster/dryer is suspended in a turbulent windstorm of hot air. This technology is currently being tested for drying or heat-processing a variety of products including: composted manure, leaf and grass compost, city sewer sludge, meat and fish processing waste, food processing waste, and ground poultry mortalities.

Flash dehydration is similar to fluidized-bed drying, except the material flows along a channel of super-heated air instead of floating on a bed of hot air jets. Like fluidized-bed drying, flash dehydration can be used to dry many types of wet wastes, but it is most applicable for drying large amounts of animal byproducts and offals. The current equipment can dry about four tons of wet offal per hour and it is very energy efficient compared to other drying methods. It can evaporate 500 gal. of water per hour, using one part fuel to evaporate 12 parts of water. The high temperature and short dwell time causes little damage to protein quality. If sterilization of the product is required it can be extruded and dehydrated to about 20% moisture. The cost to dehydrate turkey mortalities to 20% moisture is about $27 per ton of final product and $40 per ton if followed by extrusion (Nesbitt). These costs assume $1.10/gal. for fuel, 12 cents/kwh and 75 cents per ton maintenance. Neither flash dehydration nor fluidized-bed drying have yet been use to recycle pig mortalities but probably both will be used in the future.

Take-Home Message

The age of the environment started in the 1980's and will continue into the 21st century. The swine industry has adopted, and will continue to adopt, those technologies that enable it to meet rigid environmental standards and those that it can use to increase the value of its waste products. For farms that do not have ready access to rendering facilities, composting has been shown to work particularly in the warmer, southern areas of the U.S. The cold northern winters may restrict outdoor composting but it may be economical to provide space inside the hog units. Of all the techniques available to extend on-farm storage of carcasses, fermentation is the most attractive. It is working well for the poultry industry and trials are underway in North Carolina to adapt the procedures for use in swine. It is time the swine industry stopped wasting money trying to dispose of its waste. Our industry must convert its current waste products into useful byproducts. Recycling our waste will save us money and enhance our reputation.

Suggested Reading

"Composting Poultry Mortality in North Carolina" available from the North Carolina Cooperative Extension Service.