November 22, 2006 | General

Composting Livestock Mortalities

BioCycle November 2006, Vol. 47, No. 11, p. 42
Performance, composting methods, environmental impacts and biosecurity of the process are evaluated for emergency disposal of cattle by research team at Iowa State University.
T.D. Glanville, T.L. Richard, J.D. Harmon, D.L. Reynolds, H.K. Ahn and S. Akinc

A THREE-YEAR study was commissioned by the Iowa Department of Natural Resources to evaluate the practical feasibility, performance, environmental impacts and biosecurity of using composting for emergency disposal – should a livestock or poultry disease outbreak (or agro-terrorism) occur in Iowa. During that time, approximately 54 tons of 1,000 lb cattle carcasses were composted in 27 full-scale test units (each containing two tons of cattle carcasses) by agricultural engineering and veterinary medicine researchers at Iowa State University. A final report on the research was published in March 2006.
Since composting operations can be adversely affected by weather conditions, the study included six seasonal field trials – each lasting approximately 12 months – that were begun during times of the year that can pose challenging conditions for composting (spring – cool/wet, summer – hot/dry, winter – cold/dry). During the seasonal field trials, test units were extensively monitored to evaluate composting performance, environmental impacts, and biosecurity of the process. Three carcass cover materials – corn silage, ground cornstalks, and straw/manure – were evaluated in replicated field tests; these and 10 other potential cover materials also were extensively tested in the lab and mathematically modeled to characterize and predict their performance potential for use in both routine and emergency mortality composting operations.
Figure one illustrates field monitoring included: Continuous logging of internal operating temperatures in three zones (core, carcass surface, and outer envelope) to assess general composting performance and the ability to meet pathogen reduction criteria developed and used in the biosolids composting industry; Periodic measurement of internal oxygen concentrations in the three zones to evaluate the ability of the cover materials to transport oxygen to the carcass decay zone, and to transport excess water vapor and composting gases out of the pile; Periodic excavation of selected test units to observe and photograph carcass decay and to estimate the time necessary for completion of soft-tissue decomposition; Leachate capture, quantification, and chemical testing to evaluate soil and water pollution potential; Soil testing to a depth of four feet – before and after composting – to assess actual pollution impacts on soil and shallow groundwater; Collection of odor samples from the outer surface of the composting test units to evaluate air pollution potential; Implantation and retrieval of samples of vaccine strains of two common avian viruses to evaluate the potential of emergency composting procedures to inactivate viral pathogens; and Blood sampling and serum testing of specific pathogen-free poultry housed in cages near selected composting test units to assess the potential of the composting operations to retain live viruses.
The final project report, “Environmental Impacts and Biosecurity of Composting for Emergency Disposal of Livestock Mortalities,” containing data collected during the field monitoring and a full analysis, is available on the research project website at This article summarizes the findings.
Carcass Decomposition: Periodic excavation and observation of small sections of selected windrows showed that all soft tissues associated with the 1,000 lb (450 kg) carcasses were fully decomposed within four to six months in unturned emergency composting windrows constructed during warm weather, and in eight to 10 months in unturned windrows constructed during cold weather.
Internal Temperatures/Pathogen Destruction: Continuous temperature monitoring showed that test units constructed with corn silage reached internal temperatures in excess of 55°C in only one or two days following construction regardless of external temperatures, produced the highest core and carcass surface zone temperatures (usually 60°-70°C), and sustained high temperatures the longest of any of the materials tested. Test units constructed with ground cornstalks or straw and manure were generally 10°-20°C cooler than those constructed with corn silage, and sometimes took a week or more to reach peak temperatures if their initial moisture content was low.
Test units constructed with corn silage met USEPA Part 503 Class A time/temperature criteria for pathogen destruction (carcass surface zone) in biosolids in 89 percent of the seasonal units tested. Class A requirements in the carcass surface zones of straw/manure test units were achieved in 67 percent of test units, and in 22 percent of the cornstalk units. Less stringent USEPA Part 503 Class B requirements for significant reduction of pathogens were attained in the carcass surface zones of 100 percent, 67 percent, and 22 percent of the silage, straw/manure, and ground cornstalk test units respectively.
Internal Oxygen Concentrations: Reflecting the high gas permeability characteristic of ground cornstalks, mean O2 concentrations within the core, carcass surface, and outer envelope zones of test units constructed with this material exceeded 15 percent, and minimum values never dropped below 11 percent. Mean O2 concentrations in the core zone of corn silage and straw/manure test units, however, were in the five to 10 percent range during the initial weeks of the trials, and minimum values dropped below five percent. In the carcass surface and outer envelope zones, mean O2 concentrations for silage and straw/manure units exceeded 10 percent at all times, and minimum values were above five percent.
Temperature, Oxygen and Carcass Degradation: Despite substantially higher internal temperatures in silage test units, soft tissue degradation times of carcasses in silage test units appeared to be essentially the same as for those in test units constructed with ground cornstalks or straw/manure. This emphasizes several important points regarding temperature and microbial activity. First, while high temperatures are sometimes indicative of higher microbial activity, they also can occur when microbial activity is moderate but heat retention is high due to use of cover materials with good insulating characteristics. Furthermore, as temperatures rise above 60°C, microorganisms begin to die or go dormant, thereby slowing the rate of decay. Considering the higher O2 concentrations within the cornstalk test units (indicative of higher gas permeability and intrusion of cool external air), it is believed that lower temperatures within cornstalk and straw/manure test units are due mainly to heat loss – not low microbial activity – and that the similarity in carcass decay times reflects similar biodegradation rates in the interior of the piles.
Odor Release and Air Pollution Potential: A 45-60 cm thick layer of ground cornstalks, ground straw, or silage over the cattle carcasses, was effective at containing, breaking down, and masking odorous gases released during carcass decay. The odor detection threshold (ODT) for air samples collected from the surfaces of straw/manure or cornstalk mortality compost piles (during the first four weeks following construction) were similar to those reported in the literature for pond water (200-300 ODT). The ODT for silage was higher (but generally less than 1400), which was expected because of the naturally more odorous nature of silage. These odor detection levels are considered to be quite low for manure-related facilities and, due to the low ODT, small pile area, and naturally-occurring dilution between the pile and a neighboring residence, it is concluded that properly managed emergency mortality composting piles generally would not present an odor nuisance problem.
Leachate Release and Soil/Water Pollution Potential: Evidence of runoff from the emergency composting windrows was rarely noted. Leachate volumes captured beneath the test units were less than five percent of the precipitation (500-600 mm) that fell during the year. The high water holding capacity and gas permeability of the cover materials, resulting in temporary absorption and subsequent evaporation of excess water, are believed to account for their relatively low leachate release.
Soil Contamination: Statistically significant increases in chloride concentrations were noted in all depth increments of 120-cm soil cores collected beneath the composting test units indicating that leachate had penetrated to depths of 120 cm (4 ft) or more. Significant increases in percent total carbon, and percent total nitrogen were limited to the top 15 cm (6 in) of soil, occurring only beneath silage test units for total carbon, and beneath silage, cornstalk, and straw/manure test units for total N. The increases in these pollutants were moderate, amounting to less than 20 percent of precomposting concentrations of percent total carbon, and 10 to 40 percent of total N concentrations prior to composting.
Large and statistically significant increases in ammonia-nitrogen were found at depths of up to 90 cm (3 ft) beneath test units constructed with silage, and at 30 cm (1 ft) and 15 cm (6 in) depths respectively beneath test units constructed with straw/manure and cornstalks. These increases – attributed to high concentrations of ammonia-nitrogen in the compost leachate – were 40 to 160 times precomposting levels of ammonia-nitrogen in the topsoil, and are roughly equivalent to fertilizer or manure nitrogen applications of 360 to 1440 kg/ha (325-1,300 lb/acre). High residual concentrations of ammonia-nitrogen in the topsoil following composting are expected to nitrify following removal of the finished compost from the disposal site. This may lead to subsequent nitrate pollution of the subsoil or shallow groundwater. Further monitoring of soil N at the composting research site is recommended to better understand the dynamics of ammonia dissipation in the soil, and to evaluate mitigation measures that can help to minimize groundwater pollution risks.
Despite the large increases in ammonia-nitrogen concentrations in the topsoil, when compared with the groundwater pollution potential of carcass burial – the most common on-farm method for emergency disposal of livestock carcasses – the nitrogen-related groundwater pollution risks associated with composting appear to be much lower. The total mass of N contained in the composted cattle carcasses was four to 10 times greater than the increases in total N that were measured in the soil beneath composting test units. (This is the estimated total N in the carcasses, which starts out as organic N, mostly in the protein, but gets converted primarily to ammonia N during composting or subsequent leachate degradation in the topsoil.) Burial would have placed the carcass N much closer to the groundwater, further increasing the risks of groundwater pollution.
Cover Material Performance: Comprehensive physical and biological testing of 13 potential cover materials – combined with field performance data for five of those materials – suggest that water-holding capacity, gas permeability, mechanical strength, and biodegradability are the most useful variables for predicting cover material performance. Based on laboratory testing and field observations, turkey litter, corn silage, oat straw and alfalfa hay are top ranked for use in disease-related carcass disposal scenarios where production and retention of heat, and ability to retain liquid, are critical in reducing pathogens and retaining leachate in unturned windrows. These materials, and four others – ground cornstalks, wood shavings, sawdust and soybean straw – are also considered suitable for composting routine or emergency mortalities that have not been caused by disease.
Inactivation Of Common Avian Viruses: Vaccine strains of avian encephalomyelitis (AE) and Newcastle Disease virus (NDV) were reliably inactivated during emergency composting of large animal carcasses in unsheltered windrows. When the test viruses were contained in sealed vials that protected them from stress factors other than heat, survival times ranged from two days to four weeks for NDV, and one to seven weeks for AE. When the test viruses were contained in dialysis cassettes that exposed them to heat plus other stress factors, both types were inactivated within one week regardless of the season when the trial was begun, or of the type of cover material used. This does not imply that time/temperature criteria are not important factors in virus inactivation, but it suggests that other factors also play important roles in pathogen reduction.
Negative serum antibody test results for 71 of 72 pathogen-free sentinel poultry housed in cages located within a few feet of the composting test units indicate that the vast majority of the sentinel birds were not exposed to the live AE and NDV viruses (vaccine strains) that had been applied to carcass surfaces when the test units were constructed. This further suggests that 45-60 cm (18-24 inches) of clean cover material placed over the contaminated carcasses were reasonably successful at containing viruses until they were inactivated. Positive serum antibody test results (6 of 22 birds tested positive for NDV) in sentinel poultry exposed to test units whose external surfaces had been contaminated with vaccine strains of AE and NDV, confirm that live viruses do not reliably adhere to the external surfaces of emergency composting piles, and that use of pathogen-contaminated materials in the outer envelope of emergency composting windrows can expose nearby birds or animals to disease. This further emphasizes the importance of using a sufficiently thick layer of uncontaminated materials over the emergency composting piles to help insure pathogen containment.
Consistently negative serum antibody results during supplemental tests in which poultry were exposed to dust from finished compost (0 of 23 birds tested positive), and to soil beneath composting test units (0 of 6 birds tested positive), provide further evidence that emergency composting procedures are reasonably biosecure and that the composted material is safe to handle and spread.
The following general guidelines are based on results of the comprehensive three-year emergency cattle mortality composting research, as well as on practical experience with nonemergency composting practices used in the swine and poultry industries. These general guidelines are based on performance observations made under Iowa environmental conditions (temperature, wind, precipitation, soil type) and using specific types of cover materials produced in the state. They may not be appropriate for locations having significantly different climatic or environmental conditions, or when using cover materials having physical, chemical, or biological characteristics that differ substantially from the cover materials tested during this study.
Composting System & Configuration: Narrow-based windrow composting systems are recommended for emergency mortality disposal. They are practical to construct with on-farm equipment and materials, and do not require construction of special facilities (base pad, walls, cover) if the proper types and thickness of organic base/cover material are used. To promote oxygen penetration, release of excess heat, and evaporation of excess water, a long and narrow windrow configuration is preferable to a wide-based system. For full-sized (1,000 lb) cattle, a maximum base width of 16 to 18 feet is recommended (sufficient for two full-sized cattle laid side-by-side).
Properly constructed and operated emergency cattle mortality composting operations do not pose unusual pollution threats to soil, water, or air quality but should be sited observing recommended setbacks from roadways, public land, private dwellings, wells, streams, and active poultry and livestock operations, that are typically used for other animal waste facilities. To the extent possible, select a reasonably level location that will not be subject to overland flow of runoff during rainfall or snowmelt.
Base/Cover Material Selection And Thickness: If livestock death is caused by disease, use of moderately moist corn silage or a similar material that quickly produces and sustains high internal temperatures is recommended as it offers the best potential for quick pathogen inactivation. Laboratory tests suggest that materials likely to have heating and heat retention characteristics similar to corn silage include alfalfa hay, turkey litter and oat straw.
For routine or nondisease-related carcass disposal, ground cornstalks, ground soybean straw, wood shavings, sawdust, leaves, ground wheat straw, and dry bedded beef manure will sustain carcass decay and retain excess water. These materials have low potential for rapid development of sustained high temperatures, however, and are not the cover material of choice for situations where rapid pathogen reduction is desired. Dense, soil-like, or fine-textured materials similar to the soil/compost blend tested during this study should not be used for emergency carcass composting. Such materials tend to lack sufficient free air space, and are prone to compaction and moisture retention leading to further loss of free air space. This can lead to low O2 concentrations in the core and carcass surface zones of the composting pile, and very slow carcass decay.
Use of any base/cover materials that are too wet should be avoided. To test wetness, squeeze a handful tightly. If any water drips out, the material is too wet and may perform poorly due to reduced water absorption, low oxygen transmitting capacity, and high leachate production.
Long and fibrous agricultural residues must be ground (2-inch maximum length recommended) prior to use as carcass composting cover material to enhance their water absorbing capacity and to minimize formation of large voids in the outer envelope that could lead to carcass exposure, excessive heat loss, and leachate release. To minimize the risks of excessive leachate release a 24-inch deep base layer beneath the carcasses is recommended. Additionally, a 24-inch thick envelope of cover material over the carcasses is recommended to minimize the risks of both odor and leachate release.
Finally, to avoid excessive compaction and subsequent loss of free air space in the base layers of the windrow, pile heights should be limited to a maximum of 2 m for turkey litter, 1 m for dry bedded beef manure, and 0.5 m for dense soil-like materials (not recommended for emergency composting) such as the soil/compost blend. For the remaining 10 materials tested, compost modeling indicates that pile heights of up to 3 m can be used without serious compaction.
Organic Loading Rates: Every 1,000 lbs of carcasses contains approximately 650 lbs of water, so stacking of large carcasses greatly increases the likelihood of leachate production, excessive compaction of base layers, severe pile settling, and development of anaerobic conditions beneath the carcasses. To avoid these problems, it is recommended that large (> 750 lb) carcasses be composted in single layers (no stacking). Smaller carcasses may be stacked if at least 12-inches of absorptive material are placed between layers. Windrow mass loading rates of one ton (2,000 lbs) of carcasses for every 8-feet of windrow length proved successful during the study. Higher mass loading rates will increase the quantity of water in the pile and may lead to low internal O2 concentrations, reduced decay rates, and release of leachate from the sides of the windrow.
Quantity Of Base/Cover Materials: Using the recommended narrow-based windrow geometry (16-18 ft base width with pile height about half of base width) and 24-inch base and outer envelope layer thicknesses, approximately 12 cubic yards of base/cover material will be needed for every 1,000 lbs of large cattle carcasses composted in an emergency windrow system. At typical cover material densities in newly constructed windrows, this is equivalent to 1.0 ton of ground hay or straw, 1.4 tons of ground cornstalks, or 3.2 tons of corn silage. Due to the large volume of cover material required, livestock operations planning to use composting for emergency mortality disposal should plan on stockpiling sufficient quantities of cover material, or develop a plan for quickly locating and hauling sufficient material to meet emergency needs.
Windrow Operation: Windrows constructed with cover materials that are sufficiently permeable (see material recommendations) to air flow need not, and should not, be turned if mortalities were caused by disease, until soft tissues are fully decayed. Nondisease-related mortalities may be turned to improve oxygen transfer and moisture distribution, but turning of large carcasses too early in the decay process can release odors or cause undue cooling during cold weather. It is recommended to wait at least 90 days before turning heavily loaded emergency composting windrows, and extra cover material should be kept on hand to control odor releases if they occur following turning.
Site Cleanup and Remediation: Finished cattle mortality compost may include large bones that can interfere with tillage and planting, or offend nearby residential property owners. Additional tillage operations may be needed to break up or cover the bones. Use of a manure spreader equipped with a hammermill-type discharge can help to reduce the size of large bones. Screening and burial of the large bones is another option. The uppermost layers of topsoil located beneath carcass composting windrows may accumulate salts or other phytotoxic materials that suppress crop emergence and growth. Tillage of these soils may help to break up the affected layer and mix it with uncontaminated soil, thereby improving first year crop production.
Project leader for the Emergency Livestock Mortality Composting study is Dr. Tom Glanville of Iowa State University. Other members of the research team are Dr. T.L. Richard of Pennsylvania State University; Dr. J.D. Harmon, Dr. D.L. Reynolds, Dr. H.K.Ahn, and S. Akinc of Iowa State University. E-mail address for Dr. Glanville is The complete final report of the research project discussed in this article can be found at http://
THE University of Maine Cooperative Extension is sponsoring its second research conference, National Carcass Disposal Symposium 2006, at the USDA’s Beltsville Agricultural Research Center in Beltsville, Maryland on December 4-7. The first national conference was held in May 2005 in Portland, Maine. This year’s event features six presentation tracks covering the following topics: Wildlife and Marine Carcass Disposal; Biosecurity and Pathogen Research; Carcass Disposal Technology; Composting, Landfilling and Burial; Past Experiences/ Lessons Learned; and Planning for Catastrophic Events. Plenary session speakers include Nora Goldstein, BioCycle- “State of Carcass Disposal;” Bethany Grohs O’Brien, USDA-APHIS- “National Strategic Plan;” Patricia Millner, USDA-ARS-“Pathogens and Carcass Disposal;” Doris Orlander, USDA-APHIS-“Pros and Cons of Different Disposal Options;” Mike Gallagher, USDA-“National Veterinary Stockpile;” Tim Reuter, Agriculture & Agri-Food Canada- “A DNA Purification Protocol for Molecular Investigations of Compost Containing Livestock Mortalities.”
There will be a presymposium workshop on Euthanasia & Decontamination Procedures for Avian Influenza and postsymposium demonstrations of carcass management technologies including microwave, gasification, composting, digestion, incineration and alkaline hydrolysis. Details on presenters, registration and lodging are available at Other symposium sponsors include USDA, EPA, Cornell Waste Management Institute, Iowa State University, Penn State University and APHIS.

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