Composting Poultry Mortality
Proper disposal of mortality is one of the daily management responsibilities of a poultry producer. At normal mortality rates for commercial chicken or turkey flocks, producers must dispose of large quantities of birds. The weight and volume of carcasses that growers must deal with increases dramatically as poultry reach maturity (for example, 4 pounds each for broilers and 25 pounds for tom turkeys).
Disposal pits, trench burial incineration, and rendering are common methods for disposing of the mortality. Recently composting has been added to the list of available disposal options.
The best method for a particular farm depends on a number of factors, such as cost, ability to meet design requirements, and suitability for the flock size and management system. For example, burial on the farm and placement in disposal pits are poor options in areas with a high water table or shallow rock formation because it would be difficult to meet design requirements. Landfill disposal is a poor option in most areas of the state because of new regulations and limited landfill capacity.
This publication presents information on mortality disposal regulations and on the design, construction, and management of a mortality composter. Information on mortality disposal methods other than composting is provided in Proper Disposal of Dead Poultry.
Composting techniques have recently been adapted to provide sanitary degradation of poultry carcasses. In the composting process, organic materials such as dead poultry and litter are decomposed by the natural action of microorganisms. Whole turkeys and chickens, except for a few bone fragments and feathers, can be degraded within a few weeks. The composting process subjects the carcasses to temperatures high enough to destroy pathogenic bacteria normally associated with poultry disease, making the composting system biosecure. The resulting compost has chemical and physical characteristics similar to poultry litter and can be used as crop fertilizer.
Animal Disposal Regulations
North Carolina General Statute 106-403 requires that dead poultry be disposed of within 24 hours in manner approved by the state veterinarian (an officer of the Veterinary Division, North Carolina Department of Agriculture). General Statute 106-549 requires every person, firm, or corporation having a flock of more than 200 birds to provide and maintain a disposal pit or incinerator of a size and design approved by the Department of Agriculture. The purpose of these requirements is to prevent the spread of disease organisms from dead poultry to healthy birds.
Poultry composters are currently being approved on a permit basis to assure proper design and attention to environmental considerations. Poultry producers interested in constructing a mortality composter should send a written request for a permit to the state veterinarian. The request should provide information on the composter design, flock size and type, grid number and county of the farm, producer's address, location of the composter (marked on a topographical map), and name of the contracting company if the flock is under contract.
Disposal of dead birds is also regulated by the Division of Environmental Management, an agency of the North Carolina Department of Natural Resources and Community Development, whose objective is to protect air and water quality.
Designing and Managing a Mortality Composter
Determining Composter Size
The size of the composter depends on the quantity of carcasses that must be composted. For the daily mortality of broilers, roasters, commercial turkeys, broiler breeder pullets, and commercial egg pullets, the total weight of the carcasses near maturity should be considered. In contrast, for layers and breeders the average daily mortality should be considered because the weights and mortality are more uniform throughout the flock cycle for these types of poultry.
Farm mortality records can be used as a basis for mortality calculations, particularly in cases where marketing programs or other factors make weights different from normal industry standards. Table 1 shows the average mortality and weights for various types of poultry. These data can be used with the information in Table 2 to estimate the size of the composter required. It is advisable to design a safety factor into the composter to accommodate unusually high mortality rates that may occur at times. For example, multiplying the mortality in pounds per day by 1.5 would accommodate 50 percent higher mortality than normal. Emergency capacity should also be designed into the storage section.
Allowing 2.0 cubic feet for combined primary and secondary composter volume per pound of bird mortality, the required composter capacity in cubic feet per thousand birds in the flock is estimated in Table 2. Based on these estimates, the number of 5-foot by 5-foot by 8-foot bins for standard sized of North Carolina poultry units is given in the far right column of Table 2. Storage capacity for the compost that has gone through two heat cycles as well as storage for litters, straw, and other supplies should be designed as part of the facility. Storage space must be provided to allow the compost to go through a third heating. The required volume will vary greatly, depending on how often the compost will be utilized and removed from storage, but it is recommended that space be provided for storing at least a three-month supply.
aBreeder and layer values are based on average mortality rates rather than the end-of-cycle rate. For an example showing how to calculate the mortality weight, see Figure 1.
bFor a brood-grow turkey operation, the weight should be based on a combination of the two operations.
Note: Calculations are based on allowing 2.0 cubic feet combined primary and secondary composter volume per pound of bird mortality. At least two bins are needed to allow for aeration of compost even if calculations indicate that only a partial bin is needed.
aThe formula for these calculations is given in Figure 1.
bThe first number is the number of bins needed; the number in parenthesis is the calculated number of bins required.
Composter Building and Bins
The building to house the composting bins and storage areas can take many forms, and construction methods can vary, depending upon what is most feasible on a specific farm. Composting works well in an existing building if the ceiling is high enough to allow mechanical turning of the compost. Composters can be built as stand-alone units or attached to an existing building.
A few construction features are essential to ensuring that the composting process will work consistently and to assure compatibility with environmental and nuisance concerns:
Figures 2a and 2b, Figure 3, and Figure 4 are layout drawings of composters constructed as freestanding units or as an extension of an existing building. Copies of these drawings and material listings are available from county Cooperative Extension Centers. As discussed earlier, the size of the composting building should be based on the size and number of composting bins needed. The cost of materials for composters varies considerably. Materials to construct the composter shown in Figures 2a and 2b, which is sized for a 25,000-turkey operation, are estimated to cost $3,500.
Composting bins constructed inside the composting building must meet certain requirements to facilitate composting and to make it easy to turn the compost. The primary and secondary bins should be 5 feet high. Composter depth should not exceed 6 feet. The width of the compost bins should match the width of the compost-handling equipment but should not exceed 8 feet. Smaller bins make the composting process more efficient, particularly for mortality during the early part of the production cycle. The smallest bin recommended measures 3 feet in all dimensions.
Figure 2a. Litter storage shed with compost bins (isometric view)
Figure 2b. Litter storage shed with compost bins (end view)
Figure 3. Delaware two-stage composter
Figure 4. Maryland free-standing, two-stage composter
For composting to work, three components must be present in the correct ratio: a nitrogen source (birds and litter), a carbon source (straw, peanut hulls, or pine shavings), and aerobic (oxygen-requiring) microorganisms. When all three components are combined, the mixture heats naturally, reaching temperatures greater than 140 degrees F, and mortality is broken down by microbial activity to produce water, carbon dioxide, nitrogen, and carbon.
The high temperatures produced during the composting process destroy disease-causing organisms, making composting a sanitary method of mortality disposal. Ingredient proportions that will produce a carbon-to-nitrogen ration in the range from 15:1 to 35:1 and a moisture content from 45 to 55 percent moisture are essential to the composting process. A typical recipe combines 1/10 part by weight of straw, 1 part by weight of dead poultry, and 1.5 to 2.0 parts by weight of poultry litter. This mixture will achieve a carbon-to-nitrogen ratio of 25:1 with a 45 percent moisture content (Table 3).
Although optimum moisture is critical to the composting process, water need not be added if the litter has normal moisture content (25 to 35 percent). However, it may be necessary to adjust the moisture content of some dry litters (such as those from turkey brooder houses or from broiler houses with nipple drinkers) and of some wet manures (such as those from under broiler breeder slats or layer cages). For example, it may be necessary to add water to brooder litter or to litter from the scratch area in the breeder house. On the other hand, it may be necessary to add sawdust to raw manure from caged layers and breeder houses. The mortality compost after two heat cycles should have a moisture content similar to moist chewing tobacco. Material that has gone through the compost cycle can be substituted in part for the litter, but a carbon source (such as straw or peanut hulls) must be added continuously to keep the carbon-to-nitrogen ratio at the optimum level.
Layering Composting Bins
The three ingredients are layered into the bin every day in the following order: straw, dead birds, and litter, until the bin is full (Figure 5). Begin by placing 12 inches of litter on the concrete floor of the bin, then add successive layers of straw, dead birds, and litter. The bird carcasses should be kept at least 6 inches away from the side of the bin. Each day's mortality should be covered with litter immediately to avoid insect and animal pest problems. If the mortality is low, for example at the start of the flock, use only the portion of the bin needed daily, adding portions of each layer until that layer is complete. Be sure that each day's mortality is covered with the appropriate layer of litter. When the bin is full add 6 inches of litter to cap the bin.
Much like the daily mortality pickup and disposal to which poultry growers are accustomed, filling the composter is also a daily routine. Once the daily mortality has been picked up, it is weighed, and the other ingredients are weighed and layered in the proper proportions. After the grower gains experience with these weight measurements, the operations can be performed on the basis of volume using buckets and a front-end loader or other equipment. The activity takes one person about 20 minutes a day for a broiler grower with a 100,000-bird capacity or a turkey grower with a brooding capacity of 26,000.
Figure 5. Compost layering
Monitoring and Turning (Aerating) the Compost
The material in the first (primary) bin goes through a natural rise in temperature that peaks in the range from 140 degrees to 160 degrees F. Once the process has depleted the available oxygen, the temperature begins to drop, indicating that it is time to move the material to the second (secondary) bin. Using a front-end leader, the material in the primary bin is moved to the secondary bin. During the transfer process, the ingredients are mixed and aerated by keeping the bucket of the front-end loader high while dropping the material into the secondary bin. A 6-inch layer of litter should be added to the top of the secondary bin to cap it. After the material goes through a second heating, it is removed from the secondary bin and placed in storage, where it undergoes a third composting and heating cycle. The final storage cycle should take place in a shed or in a plastic-covered outdoor pile on a site designed to prevent runoff during rainstorms.
Figure 6 shows the temperature cycle of a turkey composter. Management of the composter includes monitoring the temperature cycle to determine when to turn the compost. The temperature can be measured with a 36-inch probe thermometer. When the temperature during the first heating cycle has reached its peak and has dropped for several consecutive days (for a total drop of approximately 20 degrees F), it is time to transfer and aerate the compost. After a similar temperature sequence during the second heating cycle, the compost should again be turned and aerated. It should then be transferred to a storage area. The compost is ready to spread on fields after going through three heating cycles (including a heating cycle during storage). If it is desirable to break down the ingredients further or to have a more stable compost, the compost can be aerated again in storage. It will go through the heating cycle each time it is aerated.
Using the Mortality Compost
Mortality compost can be used as a nutrient source for crops much like fresh poultry litter or manures. Table 4 shows comparative average nutrient values of poultry litter and mortality compost. Good nutrient management techniques include testing for nutrient content of any animal by-product and then applying the product according to crop needs, using soil tests as a guide to spreading rates. The mortality compost is thought to release nitrogen more slowly and over a longer period of time than fresh litter. Studies on plant response to mortality compost are being conducted.
Insects and Other Pests Associated with Composting
The insects associated with the composting of dead birds are relatively minor pests, as are scavenger animals such as raccoons, rodents, foxes, and wild dogs. All of these pests can be controlled or eliminated by proper construction and careful management of the composting process.
In general, insect pests are found in the upper 4 to 6 inches of compost or around the base of the pile. Few if any insects will be present when the material is actively composting if the moisture content is within normal limits. The heat generated by the process (140 degrees to 160 degrees F) usually deters insect breeding. Low moisture also minimizes odors that are attractive to carrion-feeding (carcass-feeding) insects.
Flies and carrion beetles serve as useful indicators of the overall "health" of the compost. When large numbers of these insects are present, it is likely that the material is not composting properly. Excessive moisture or poorly balanced balanced carbon-to-nitrogen ratios should be suspected in such cases. Once the problem has been identified and corrected, insects will no longer find the compost pile attractive.
In rare cases, insects and other pests can become a problem when compost is spread in the field. This situation generally occurs only if the compost is applied at excessive rates without incorporation and then absorbs enough water to promote fly breeding or if it is applied before the bird carcasses have completely decomposed.
Flies associated with bird mortality composters will always be present at levels similar to the normal background population for the farm. A well-designed and well-managed composter will not contribute to either the number or species of flies already present in the area. The same can be said for other insects and animal pests that may be found in or around composters. The following suggestions will minimize or eliminate pest problems.
The authors acknowledge the University of Maryland Extension Service, which conducted the original mortality composter work, and Auburn University Extension and University of Arkansas, whose literature provided some of the information used in this publication. The North Carolina Department of Agriculture, Veterinary Division, and the Soil Conservation Service are also recognized for assistance in developing the information presented in this guide. Figure 3 and Figure 4 courtesy
of the Cooperative Extension Service, University of Maryland System.
May 29, 2007