PRODUCTION TOOL

W Morgan Morrow, BVSeMS,PhD; and Peter R Ferket, BSe,MS,PhD

Summary - We explored options for disposing of dead pigs, including some recent technologies developed for the poul-

try industry. The methods, including trench buria4 disposal pits, incineration, composting, as animal feed, extru-

sion,fluidized bed drying, flash dehydration,freezing,fermentation, and acid preservation are described. The relativeadvantages and disadvantages of each method, including cos~ impact on the environmen~ and ability to destroy patho-

gens are compared.

Increased public concern for the environment and result-ing stricter regulations governing the disposal of deadpigs present a new challenge for the hog industry. The

volume of dead pigsproduced annually is daunting - a 1000-sow farrow-to-finish farm with:

. 7%mortality in the sow herd,. 10%mortality in the neonatal phase,. 5%mortality in the nursery phase,

. 1%mortality in the growing phase, and. 1%mortality in the finishing herd

will produce approximately 20 tons (1.8x1Q4kg) of dead pigsin one year. In the past, these pigs have typically been ei-ther buried, incinerated, or taken for rendering. Unfortu-nately, these three disposal methods are now less acceptableor unavailable. Buried animals can contaminate ground wa-ter and smoke from burning animals will contaminate theair. Manyrendering plants are closing,leaving fewer hog op-erations with that option. The industry's challenge is to findinexpensive, environmentally-friendly alternatives (that donot spread disease) for disposing of dead pigs.

The poultry industry has developed two techniques-composting and fermentation - that the swine industry canpotentially use. However, all American states regulate thedisposal of dead animals and state authorities must firstapprove these alternative techniques before they can beimplemented in the field.

Disposal procedures:On-farm

Most pig carcasses are disposed of on-farm: they are buriedin a trench or disposal pit, or burned. The major advantage

WMM,Department of Animal Science; PRF, Department ofPoultry Science: North Carolina State University, Raleigh,North Carolina 27695

of on-farm disposal is biosecurity. Outside collection trucksneed not visit the farm nor must farm trucks risk contami-

nation when visiting a rendering plant or central collectionsite.

Trench burial

Because trench burial is such a cheap and efficient disposalmethod, it is used extensively worldwide. Usually, a trenchlarge enough to accommodate the carcasses is dug with abackhoe. Once buried, the pigs slowly decompose until af-ter a few years they are unrecognizable. All major hog-pro-ducing states approve of trench burial. Some states specifya minimum depth of either 3 or 4 ft (0.9 or 1.2m) and somespecify a maximum depth of 6 or 8 feet (1.8or 2.4m). Also,some states mandate that the material covering the trenchbe from 30 to 48 in (0.76 to 1.2m) deep. Hermel (NationalHogFarmer, March 15,1992;pp 34-42) reviewed state require-ments governing the dimensions of the trench and theirproximity to water supplies.

The major disadvantage of burial is that the carcasses cancontaminate groundwater supplies,particularly in areas withlight soil and a high water table. In colder areas it is diffi-cult, if not impossible, to dig frozen ground during the win-ter months. Also,predators can uncover the carcasses,whichis unsightly and a disease risk. Probably because it is such abasic disposal technique, there is no research documentingthe relative advantages or disadvantages of trench burial.

Disposal pitsAlthough disposal pits are more common in the poultry in-dustry than the swine industry, they have some advantagesover other burial techniques. I~is easy to build disposal pitsthat have solid walls and a solid top but with a permeablebase so carcasses can be added continuously (Wineland MJ,1990, Proc Natl Poultry Waste Mgmt Symp, pp 69-74). Al-though there is some aerobic activity on the top of the pile,decomposition is primarily accomplished by various micro-organisms that anaerobically digest the polysaccarides, pro-teins, and fats of the carcass into substrates for methogenic

Swine Health and Production - Volume 1, Number 3 7

bacteria. This decomposition process produces methane, car-bon dioxide, and other malodorous compounds, and dependson the successive interaction of a variety of organisms!thatare temperature-, pH-,and oxygen-dependent.If the environ-ment favors the growth of acid-forming bacteria, decompo-sition-inhibiting fermentation can occur (see Fermentationsection). For poultry, Lomax and Malone (1988, Prof IntiSummer Mtg of Am SOGof Ag Eng) showed that decomposi-tion was faster at 35°Cthan at 24°C,permitting higher load-ing rates.

Interestingly, a variety of insects are found in disposal pits.By consuming carcass flesh and burrowing through the sur-face of the skin, they increase the surface area accessible tomicroorganisms, thereby positively contributing to the de-composition process (Rives D, et aI, 1992,PrOfNatl PoultryWasteMgmt Symp, pp 409-412).Provided the pit is rainproof,little water will leak from the base because the decomposi-tion process produces little water. Unfortunately, anaerobicdigestion can generate hydrogen sulphide in concentrationsthat can exceed human safety levels (MaloneEW,1988,PrOfNatl Poultry WasteMgmt Symp, pp 73-75).For a review ofthe construction and operation of on-site disposal pits forpoultry read Sweeten and Thornberry (1984,PrOf16th AnnTexasBroiler Symp).

IncinerationAlthough incineration eliminates all pathogens, it is costlyand produces pollution. Incinerators can be made from oldlow-pressure (LP) gas tanks for less than $1000(Fig 1). Afully-insulated incinerator with afterburners to decreasepollution can be purchased for less than $2000.ConvertedLP gas tanks must often be replaced after 5 years; the pur-pose-built burners last much longer. Operation costs includethe grates, which must be replaced every 2-3years, and theoil or gas fuel. The 160-sow,farrow-to-finish demonstrationfarm at Rocky Mount, North Carolina averaged 844 gal(3200 L) fuel oil for each of the 8 years ending in 1990.At$1per gal, the fuel oil alone would amount to $5.27per sowper year.

Fig 1.- Incineration

All major hog-producing states permit the incineration ofhogs but do not allow hogs to be burned in a field. Of allthe methods of disposal, incineration generates the mostpublic complaints and is therefore the least likely to remainan option (Murphy DWand Handwerker TS,1988,PrOfNatlPoultry Waste Mgmt Symp, pp 65-72).

CompostingThe poultry industry, which has experienced increasing dif-ficulty in disposing of its dead birds, has developed an al-ternative in composting (Fig 2). Composting uses wasteproducts (such as dead pigs, straw, and poultry litter) andconverts them into an odorless,inoffensive, generally patho-gen-free product that can be used as a soil amendment ororganic fertilizer. The process of composting carcasses is thesame as that used to compost garden waste. A succession ofmesophilic and thermophilic microorganisms, including bac-teria, fungi, and actinomycetes, feed on the organic sub-

Fig2.- Composting

strates to produce carbon dioxide, water, minerals, and a sta-bilized organic matter called humus. The speed and effi-ciency of this aerobic process depends on the temperature,nutrients, moisture, availability of oxygen, and particle size.

TemperatureBecausea compost pile contains a diversity of temperature-sensitive organisms, some decomposition occurs at virtuallyany temperature; however, the optimum temperature formicrobial activity is < 55°c.(McKinleyVL,et al. 1985.BioGycle26:47-50.)Decompositionof pig carcasses slows considerablyin winter but increases in the spring when temperatures rise.In North Carolina, our compost piles consistently reach tem-peratures > 55°C,which killed most of the Salmonella, andall of the Erysipelas,in broth cultures placed throughout thepile. Poultry compost piles routinely reach 70°C.The tem-perature can be controlled by adjusting aeration and mois-ture and covering the pile with an insulating layer of thecarbon source (e.g. straw) each time pigs are added to thepile. The optimum temperature for the pile, then, must be a

Swine Health and Production - May, 19938

compromise between the temperature range that favors mi-crobial activity and that which will result in the fastest de-composition (45°C-50°C) and the temperatures at whichpathogens can be destroyed (> 55°Cfor Salmonella, some ofthe most heat-resistant pathogens).

Nutrients

Composting microorganisms need appropriate nutrients towork effectively. The most important are carbon and nitro-gen. Phosphorous, sulfur, calcium, and trace quantities ofother nutrients are required for cell growth. A carbon: ni-trogen ratio between 20 : 1 and 35:1 is optimal. Above thatrange, decomposition slows. Below a ratio of 15:1,nitrogenis lost as ammonia, which reduces the value of the humusand creates an odor problem. Adjusting the components ofthe pile to get the correct ratio is the key to successfulcomposting. The recipe we have used successfully is:

. 100Ib (45.4kg) of dead pigs,. 150Ib (68.0 kg) of turkey litter, and. 10Ib (4.5 kg) of wheat straw.

MoistureSince water is essential for nutrient solubilization and cell

protoplasm, a moisture content below 20%can severely in-hibit the decomposition process.Too much water will blockair movement, causing the pile to become anaerobic. Theoptimum moisture level is 45%-55%.We have achieved thislevel by adding 4 gal (15L) water to the above recipe.

OxygenDecomposition in the compost pile is fastest when aerobicconditions prevail throughout. In reality, aerobic conditionsprobably exist only at the periphery of the 6x4x5 ft (1.8x1.2x1.5m) piles we construct, which slows decomposition. Com-mercial composting operations for municipal waste can me-chanically aerate their piles by periodically turning the piles,inserting perforated tubes, dropping the piles from floor tofloor, or pumping air through them. Too much aeration candehydrate the pile and waste heat so that the piles do notreach temperatures sufficient for proper decomposition(45°C)or pathogen destruction (> 55°C).In practice, the pilesare turned 2-3 days after each temperature peak. This aer-ates the piles and restarts decomposition. It takes 2-5 daysafter turning for temperatures in the pile to peak again.Emulating the success of composting dead birds, we havefound that it is sufficient to turn the pile three times.

Particle size

The smaller the particle size of the compost, the greater thesurface area available to the microorganisms.However, somematerial must be large enough to provide structural supportand to trap the oxygen needed for aerobic digestion.Murphy(1992,ProcNat! Poultry WasteMgmt Symp,pp 33-40)hasdemonstrated that by cutting into and pulling apart the tho-rax, abdomen, and muscles, it is possible to compost pigsweighing up to 300 Ib (136 kg). In practice, pig carcasses of

less than 30 Ib (14 kg) need not be cut open, and the strawthat we have used provides carbon, structural support, andthe necessary aeration.

The location, construction, operation, and precautions weused for composting dead pigs are similar to those requiredfor poultry (as detailed in the publication "CompostingPoul-try Mortality in North Carolina" available from the NorthCarolina Cooperative Extension Service).The North CarolinaState Veterinary office has authorized us to conduct experi-ments to tailor those requirements to the swine industry.

As feed for animalsIn deference to the mink industry, the state of Minnesotapermits the feeding of carcasses specifically to fur animals.The hazard of feeding dead pigs to livestock is well knownto any farmer who has lost dogs and cats that had access topigs that died of Aujeszky'sdisease (pseudorabies). However,some states allow producers to feed carcasses to animals(other than fur-bearing ones). One 2000-sow hog farmer inPasco County, Florida is profitably feeding processed deadhogs and poultry to alligators that are slaughtered for theirmeat and hides? Also,a hog farm in Singaporefed all its deadpigs to crocodiles that were slaughtered for the local leatherindustry. \

Disposal procedures:Off farmThere are two main methods to dispose of pig carcasses off-farm:

. Taking them to a landfill: For routine use,or whensupply exceeds disposal capacity, producers cansometimes take pig carcasses to a landfill. How-ever, many municipal authorities now refuse pigcarcasses even though state regulations permittheir disposal in a landfill. Landfills can charge$10-$30per ton ($11-$33per tonne), which is costprohibitive. Landfills raise the same concerns ofgroundwater contamination and predators as on-farm burial.

. Selling them to a rendering facility: Renderingwas and is the best means for converting car-casses into a valued, biologically safe proteinbyproduct. Unfortunately, because world pricesfor fat, protein, and hides are depressed, fewerrendering facilities are in operation. Transportingcarcasses can be prohibitively expensive if therendering facility is too far away. Somecountieshave designated sites for the central pickup ofcarcasses. Central pickup and delivery to a ren-dering plant is an environmentally sound andefficient method for recycling pig and poultry

Swine Health and Production - Volume I, Number 3 9

Table I. - Advantages and disadvantages of extrusion processing.Reprinted courtesy of Feedstuffsmagazine,March 9, 1992,Vol 63 #9 p.21.

Protein

Starch

Fat

Fiber

Vitamins

Minerals

Advantages

Denaturization; inactivation of growth inhibitors;breakdown of secondary bonds; formation ofnew bonds

Improves digestibility by gelatinization andexpansion; break down to simple "sweet"components

Mixing; oil extraction; increase fat digestibility;encapsulation of oil; formation of fat and starchcomplex (I: 10 ratio); improve stability byinactivation of lipolytic enzymes

Bulk density reduction; increase nutrient andfiber digestibility

Not applicable

Not applicable

Microorganisms Destruction of bacteria, molds, fungi, yeast, andprotozoa. Some extruders destroy viruses andmold spores

Toxic

compounds

Palatability

Feed form

Destruction of glycoalkaloids; reduce gossypoltoxicity; detoxify aflatoxin with the addition of1.5% ammonium hydroxide; destruction ofallergins

Increased sweetness, unpleasant volatile flavorcomponents flushed off during expansion;improved texture

Versatilityof feed density; texture and shape;improved mechanical durability of finished feed;no need for pellet binders, improve waterstability

Disadvantages'

Destruction of amino acids and cross-linkingreactions of polymers with protein andcarbohydrates

Hydrolysis of carbohydrates

Oxidation of lipidsand flavor components

Not applicable

Loss of vitamin activity, especially with A, D, E, C,

B" B6'pantothenate, biotin, and foliates

Possibly phytate complex with zinc, magnesium,and phosphorous

Not applicable

Not applicable

Development of undesirable flavors by reactionproducts

Not applicable

'Disadvantages are dependent upon the severity of the cooking process, which can be altered by dwell time, screwrotation, speed, and moisture.

carcasses.However,becausethe central siteis vis-ited by many producers, biosecurity is crucial andstrict policies must be established and adhered to(Parsons J and Ferket PR, 1990, PrOf Poultry Serv

Short Course,pp 7-20).Constructioncosts can varydepending on the amount of work the site re-quires. Prices received for the carcasses also canvary considerably. Greene County in North Caro-lina profitably operates a site that accepts bothpoultry and livestock.

In addition to these off-farm disposal options, there are sev-eral off-farm disposal technologies that swine producers areusing more and more frequently:

ExtrusionExtrusion is not a new technique for the food industry. Ithas been used to processhuman food for more than 50 yearsand it is the foundation of the pet food industry, produc-ing 13billion lb (5.9x1O6kg) of product with a market valueof $8billion annually. High-quality feed products have beenmanufactured from:

10 Swine Health and Production - May, 1993

. extruded whole chicken carcasses,3

. poultry offal and feathers (Blake JP, et aI, 1990,Proc Midwest Poultry Fed Mtgs;VandepopuliereJM,1990,ProcNat! Poultry WasteMgmt Symp, pp64-67), and. hatchery waste.4

soybeans and creep feed, individual farmers may be able tojustify the cost.

Fluidized-bed drying and flash dehydrationFluidized-bed roasting/drying technology was developed afew years ago for roasting full-fat soybeans. A centrifugalfan blows air over a natural gas or propane burner, heat-ing the air to 300°F (150°C)and suspending the raw mate-rial in a turbulent windstorm of hot air. This technology iscurrently being tested for drying or heat-processing a vari-ety of products, including:

Fig3.- Single-screwextruder

. compostedmanure,. leaf and grasscompost,. city sewer sludge,

. meat and fish processing waste,. foodprocessingwaste,and. ground poultry carcasses.

Flash dehydration (Fig 4) is similar to fluidized-bed drying,except that material flows along a channel of super-heatedair instead of floating on a bed of hot air jets. Like fluid-ized-bed drying, flash dehydration can be used to dry manytypes of wet wastes, but it is most appropriate for dryinglarge amounts of animal byproducts and offal. The currentequipment can dry about 4 tons (3600 kg) of wet offal per

Material is fed into a raw material bin, then to a mixer, andfinally into the extruder, which works by using friction tocreate heat, shear, and pressure. In theextruder, a screw (or screws) forcesthe material through a seriesof baffleswhere temperatures reach U5°C-155°Cand pressure reaches 20-40 atmo-spheres (2.0x1O6-4.1x1O6pa) for about30 seconds. The sudden decrease inpressure as the product leaves the ex-truder causesit to expand and lose 12%-15% of its moisture. The hightemperatures and pressure associatedwith the extrusion process effectivelyinactivate bacteria, molds, and viruses(Reynolds D, 1990,ProcMidwest Poul-try FedMts) (Table 1).

Single-screw systems (Fig 3) are mostcommon in the industry, probably be-cause they are about 50% cheaper(Hauck BW, 1990, Proc 33rd Ann PetFood lnst Cont). However, double-screw systems are better able to copewith the high-moisture ingredientsand would therefore be more appro-priate for the disposal of dead pigs.

If extrusion is used to processcarcassesit will probably be done centrally be-cause of capital costs. However, if itcan also be used to extrude full-fat

Fig 4.- A flash dehydrator. I: oil or gas burner; 2: preheater; 3:fat press; 4:agitator; 5: drying tower; 6: classifier; 7: cyclone; 8: airlock; 9: rotary screen;10:fan.Figurecourtesy of Ziwex Recyclingtechnology,North Carolina (ZiwagAG).

Swine Health and Production - Volume I, Number 3 11

hour and it is very energy efficient compared to other dry-ing methods. It can evaporate 500 gal (1900 L) of water perhour, using one part fuel to evaporate 12parts of water. Thehigh temperature and short dwell time causes little damageto protein quality. If sterilization of the product is required,it can be extruded and dehydrated to contain about 20%moisture. The cost to dehydrate turkey carcassesto 20%mois-ture is about $27per ton ($30/1000kg) of final product and$40 per ton ($44/1000 kg) if followed by extrusion (NesbittD,1992,Ziwex RecyclingTechnology,USA,personal commu-nication). These costs assume $1.10per gal ($0.29/L) for fuel,$0.12per kilowatt-hour (kWh) and $0.75per ton ($0.83/1000kg) maintenance. Neither flash dehydration nor fluid-ized-bed drying have yet been used to recycle pig carcasses,but both will probably be used in the future.

Storage techniquesThe poultry industry is developing several intriguing tech-nologies that enable carcasses to be stored on-farm untilenough accumulate to make a trip to the renderer feasible.These techniques may be adapted for use in the swine in-dustry.

FreezingFreezing was one of the earliest methods the poultry indus-try used to extend the on-farm storage time of poultry car-casses. Recently, a large poultry integrator has developed apurpose-built freezer to hold dead broilers. They plan to useit extensively for preserving carcasses before taking themto a renderer. Each freezer will hold about 1ton (0.9 tonne)of dead broilers. The company estimates the electricity costsat about $1.20per day or $0.01per pound ($0.02/kg) of car-cass (assuming $0.08per kWh). These units may soon be gen-erally available for about $2000.

Fermentation

First proposed in 1984 by Dobbins (proc Nat! Poultry WasteMgmt Symp), fermentation is an anaerobic process that canbe used to store chicken and turkey carcasses for at least 25weeks and produces a pathogen-free and nutrient-rich silageend product (Parsons and Ferket, 1990, Proc Poultry ServShort Course,pp 7-20).5Sanders (1990, Proc Env Sound AgCon/) recently conducted an extensive review on the sub-ject. Fermented poultry offal, fed at up to 20%of growing-finishing pigs' ration, does not depress gains or increasefeed: gain ratios.6Unfortunately, no one has documented theproduction efficiency of feeding hogs the silage from fer-mented whole birds or pigs.Fermented carcasses can also beused in mink or fox feed, extruded aquaculture feeds, andruminant silage.

The bacteriocidal and virucidal activity of fermentation de-pends on the pH and prevailing temperature of the fermen-tation unit. A pH greater than the optimum 4.3-4.5(Murphy

DW,et al. 1990 ProcNatl Poultry Mgmt Symp: pp 56-63) canresult in a secondary fermentation that spoils the silage.Viruses labile to low pH do not survive fermentation; inac-tivation occurs rapidly at 40°C,but more slowly at lower tem-peraturesJ Mostimportantly, in fermented silage,Aujeszky'sdisease virus (pseudorabies virus) is rapidly inactivated at20°C-30°Cbut survives 2 days at 10°Cand 9 days at 5°CJTheoptimum temperature for fermentation is about 35°C,butsilage temperature usually matches ambient temperatures,indicating that Aujeszky'sdisease virus may not be inacti-vated in colder regions.Fermentation with Lactobacillusaci-dophilus destroys many bacteria including Salmonella Spp,8Salmonella typhimurium,9 and Clostridium botulinum typeE.1O

Typically, carcasses are prepared for fermentation by:

. grinding them to 1 in (2.5cm) or smaller particles(the grinding aids in homogenizing the ingredi-ents);. mixing them with culture inoculant and a fer-mentable carbohydrate (CHO)source (for lacticfermentation, lactose,glucose,sucrose,whey, wheypermeate, and molasses are all suitable as a CROsource; condensed brewers solubles are a particu-larly appropriate CHOsource because they are afermentation byproduct and silage pH rapidlydrops when they are used); and then

adding them to the fermentation container (anysize noncorrosive container that is sealed and

vented for carbon dioxide [Parsons and Ferket,1990,ProcPoultry Serv Short Course,pp 7-20];55-gal drums are commonly used).

.

Recently, investigators varied the recipe to include a proteo-lytic yeast (Hansenula montevideo) instead of Lactobacil-lus for the inoculant and an out-dated, nondiet soft-drinksyrup for the CHOsource.The result was satisfactory (MaloneGW.1992.ProcNatl Poultry WasteMgmt Symp, pp 49-55).

Under optimal conditions the pHof fresh carcassesis reducedfrom 6.5 to less than 4.5 within 48 hours. A properly pre-pared silage is semisolid,will keep for months, and is readilyaccepted for rendering.

Acid Preservation

Ground, split, or punctured dead broilers can be preservedon-farm at least 1 month in a 3.4%sulfuric acid solution ata cost of $0.10per lb ($0.22/kg) carcass (Malone GW,1988,Proc Natl Poultry Waste Mgmt Symp, pp 73-75).When thisacid-preserved product is rendered, it has the same nutritivevalue as regular poultry-byproduct meal.Preserving dead pigsin sulfuric acid has not been tried, but it eventually maybe an inexpensive on-farm method for storing carcasses.Thesafe handling of sulfuric acid stock solution is the primaryconcern.

12 Swine Health and Production - May, 1993

The age of environmentalism began in the 1980sand willcontinue into the 21stcentury. The swine industry will con-tinue to adopt those technologies that enable it to meet in-creasingly rigid environmental standards and those that itcan useto increase the value of its waste products. It is timethe swine industry stopped wasting money disposing of itswaste and began converting these waste products into use-ful and valuable byproducts.

References

1.La Reviere JWM. Microbial ecology of liquid waste treat-ment. In: AdvancesIn Microbial Ecology,Vol 1,Plenum Press,New York, NY. 1973:215-259.

2. Walker WR, Lane TJ, and Jennings EW.Alligator produc-tion in swine farm lagoons for disposal of dead pigs. JAnim

Sci. 1992; 70:Supplement 1. 30.

3. Hague AKMA, Lyons 11,Vandepopuliere JM. Utilization ofground whole hens in broiler diets. PoultrySci.1990;66:1,1-10.

4. Miller BF. Extruding hatchery waste. Poultry Sci.1984;43:1284-1286.

5. Murphy DW and Silbert SA.Preservation of acid nutrientrecovery from poultry carcassessubjected to lactic acid bac-teria fermentation. ] ApplPoultryRes.1992;1:66-74.

6. Tibbetts GW,SeedeyRW,and McCampbell HC.Poultry of-fal ensiled with Lactobacillus acidophilus for growing andfinishing swine diets. ] Anim Sci. 1987; 64:182-190.

7.Gilbert JP,Woolley RE,Shotts EB,and DickensJA. Viricidaleffects of Lactobacillus and yeast fermentation. Appl andEnviron Microbiol. 1983; 46:452-458.

8. Khan M and Katamy M. Antagonistic effects of fatty ac-ids against Salmonella in meat and bone meal. Appl.Microbiol. 1969;17:402.

9.Slywester K and Wartenberg 1. The ensilage of pirosilorybtype as the source of the possible infection with Salmonella

typhimurium.

10.Wirahadikusumah S.Preventing Clostridiumbotulinumtype E poisoning and fat rancidity by silage fermentation.

lantbrukshogsk Ann. 1968;78:477.

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