On-Farm Methods For Composting Livestock Carcasses
Even with the best management of herds and flocks, animal mortalities do occur, and low-impact disposal of these carcasses often provides a challenge to the producer. The challenge of disposal involves burial sites, water table, frozen ground and odor. In addition, the proximity of neighbors and the prevalence of scavengers such as coyotes and dogs often places a strain on the relationship of a farm and its neighbors. The odors of stored manure and silages will often result in complaints to local officials as will odors resulting from rotting carcasses when above-ground disposal has occurred.
In the poultry industry where large numbers of birds may be involved, there has been a need for methods to dispose of daily mortalities as well as catastrophic losses. Some of these methods have been developed and refined by Dr. Lewis Carr at the University of Maryland, Eastern Shore. With broiler-sized chickens (4-8#) Carr has worked out a bin construction in which dead birds are composted in a tidy and simple way. The resultant compost can be land-applied, thus assisting in fertilizing crops. With larger livestock body masses represented by cows, horses, swine, and sheep, producers generally are faced with two choices for carcass disposal. When possible, most producers choose to bury an animal in some remote location. On many farms, terrain, rocky soil, or hard-pan layers often mean time consuming and often incomplete method of disposal. In winter months when the ground is frozen, carcasses are often left on the surface of the soil. With either choice, coyotes, dogs and other scavengers will often move body parts around and with fluctuations in ambient temperatures, odors are often generated. In some locations with high water tables, there is a potential for contamination of ground water by fluids from rotting carcasses.
COMPOSTING - A Definition
Composting is a process whereby bacteria reduce the volume of organic matter by degrading plant or animal tissues into common elements with the production of heat, CO2, and water.
THE PROJECT - Theory
When animals are buried, they become isolated in an oxygen-free environment. The bacteria that can survive in the absence of oxygen do decompose carcasses very slowly, often with generation of volatile compounds that can be quite smelly. This process without oxygen is commonly called rotting! Composting is a slow "cooking" process which needs air.
With composting, carcasses are no different than any other organic material (leaves, manure, etc.) except that the nitrogen (N) level is higher. For successful composting there must be a few essential elements for the bacteria to function:
(b) food (Carbon:N ratio is important;
i.e. a balanced diet for the bacteria)
(c) oxygen (air)
When carcasses or manure (high N) are composted, particular attention must be paid to get enough C in the form of straw, sawdust, shavings, or hay such that about a 25:1 (C:N) ratio exists and that moisture levels are in the 40-60% range.
THE PROJECT - Objectives
Our objectives for this project were to test the ideas surrounding an above ground method that farmers could adapt to their livestock operations. We reasoned that any procedures we might devise should require minimal investment, utilize readily available on-farm equipment and materials, and finally be simple enough in its application that farmers would continue to use it.
THE PROJECT - Methods
With the above-mentioned understanding of what conditions should be ideal for composting, we set out to examine methods for on-farm composting of carcasses. Since most of the Maryland work with poultry mortalities had been done with constructed bins, we wanted to determine if a windrow method could be devised such that all livestock mortalities (including chickens) could use the same method. In addition, we set out to see if by the use of perforated 4 inch drainage pipe situated beneath the carcasses would allow more infiltration of air (oxygen) and thus speed up decomposition. We monitored the progress of the degradation process by measuring the temperatures of the windrow in the vicinity of the body mass.
A windrow of typical horse stable bedding and manure 60 feet long, 4 feet deep and 10 feet wide was placed in an enclosure at the UMass Dairy Farm in South Deerfield, Massachusetts. As with most horse stable residue it was volumetrically 90 percent sawdust, 1-2 percent hay, and 8-9 percent actual horse manure. The carcass(es) of the species in question was/were placed atop the pile, and an equivalent depth of horse bedding was used to cover the carcass(es). No turning of the pile was done. The following species and carcass weights were evaluated:
Table 1. Compost Temperatures of Carcasses
Species & Carcass Wt Temperatures (degree F) after:
2 Weeks 4 Weeks
60 - 8# chickens (aerated) 153.1 157.9
1 - 85# stillborn calf (aerated) 135.0 109.1
1 - 300# pig (aerated) 142.1 143.5
300 - 9# chickens (aerated) 158.9 151.2
1 - 100# newborn calf 135.9 137.9
2 - 400# sows 163.5 150.8
1 - 40# lamb 128.2 120.3
1 - 1200# cow (aerated) 146.6 141.7
1 - 1300# cow 142.9 139.2
Temperature Measurements. Generally a week to ten days elapse following placement of the carcass before surrounding temperatures elevate dramatically. Since the new material being added to cover the process is freshly aerated, there is a slight temperature spurt within 2 days that stabilizes at or near 110 degrees F. Since the pile was never turned for fresh oxygenation, we measured what was happening as the tissue degradation supplied nutrients to compost bacteria.
With these limited data, it does appear that aerating the pile allows for higher temperatures to be achieved. With the perforated tile in place, flies were observed going in and out of the tile and odors could be detected in the area of the tile ends. Following the observation of the flies, we placed a screen over the tile and observed flies try to enter. We could also see that fly larvae began to try to escape the heat by crawling to the surface or into the tiles. Many birds learned that this could provide much food and would perch around the enclosure and await the appearance of the larvae.
Temperature and Disease. The nature of the process does involve thermophilic (heat loving) bacteria and certainly the temperatures generated (140 - 160 degrees F) over a period of 4 weeks should kill off most pathogens in those carcasses where passive aeration was provided. In the remaining portions of the pile where temperatures did not get up to 140 degrees, there would be a risk of not removing all disease organisms. In the Maryland trials and in some additional trials done at Delaware, when the temperature of the compost dropped to the 120-130 range, a bucket loader was used to turn the pile of dead chickens, thus providing a fresh supply of oxygen. Pile temperatures did return to the 140-150 degree F range.
Odor. Many people have been skeptical concerning the composting of large animal carcasses. Although the process is not free of odors, we were pleasantly surprised to find that none of our workers or visitors even noticed any change in the odor level about the farm. The control of odor is the result of two things:(a)adequate oxygen to provide for a "cooking" rather than anaerobic "rotting", and (b) the bedding material used both beneath and above the carcass was sufficiently absorbent to prevent the fluids generated from reaching the surface.
Predators in the area of the farm include coyotes, dogs, raccoons, and skunks. It was observed on two occasions that coyotes were attempting to locate the source of occasional odors from the pile, but they never were able to do that. Skunks, however, seemed to be able to locate the carcasses and would burrow into the pile and retrieve small bones. On one occasion, a dog was able to dig into the pile and retrieve a bone with some flesh on it. However, it did not carry it away.
Bones. One drawback in the process of composting adult whole large animal carcasses is the fact that the major limb bones and skulls will not be significantly degraded by composting. The bones from younger animals which were growing seem to have been made more brittle by composting and would probably be fragmented by going through a manure spreader. Since bones are various salts such as calcium carbonate and calcium sulfate, deposited around a protein matrix, in time they will probably disintegrate. In the 1920's and 1930's, farmers were encouraged to pulverize the bones from dead animals and apply the resulting material to their fields. There is not an easy way to do this, and at least the major bones could be placed back in a compost medium after separation from the pile.
A. Following our trials with composting various livestock species, we feel that most producers can make the process a successful method on their farms. This process (1) eliminates the need for burial areas; (2) is a natural biological process; (3) produces a material that is relatively inoffensive; (4) creates a product that can be applied to the land; (5) reduces the possibility of runoff contamination and ground water contamination; and (6) is relatively easy to maintain
B. We would suggest that each farmer who desires to try this method have the following materials on hand for the process: 1. a front end loader for turning the pile and moving materials; 2. a 36-inch long compost-type thermometer (stainless steel); 3. dry bedding or manure pack that is not caked, or horse stable waste with sawdust and straw.
C. We suggest that a pile (windrow) be created such that there will always be space to add new carcasses and that a stockpile of similar material be maintained for covering carcasses. This stockpile should be relatively dry and contain a lot of bedding (high carbon) material.
D. We suggest that the thermometer be left in the pile adjacent to the carcass and monitored weekly. When temperatures drop below 125-130 degrees F, a front end loader should be used to move the remaining carcass a few feet to either side to be covered again. This will reactivate the cooking process and mix the material. NOTE: You will generate some odor for a few minutes until covering has re-occurred. Monitor temperatures again and turn 2 or 3 more times.
E. After turning the material and seeing no remaining soft animal parts, the material can be left in place or spread on the land as needed. As bones appear, they can be all placed in one part of the pile or can be ground, smashed or pulverized for land application.
F. Based on our experience, there will be some freezing and thawing of the surface during the winter. This can slow the composting process and care should be taken to provide for at least 2-3 feet of cover to help insulate. In addition, as you choose a site for the windrow, orient the length of the windrow with North and South such that only the end of the windrow is facing a cold exposure.
G. The windrow should be oriented lengthwise with the slope of the land so that water from rainfall and snow will not puddle against the pile. If possible select a site where the slope is no more than 3 or 4 percent and on an area where tractors can maneuver under all weather conditions.
William E. Graves
Dept. of Veterinary and Animal Sciences
University of Massachusetts Amherst
Crops, Dairy, Livestock News. Vol. 2:1, Spring 1997