The practice of composting to manage on-farm swine mortalities has increased from 10.5% in 1994 to nearly 36% in 2006, according to data supplied by USDA’s Animal and Plant Health Inspection Service.
Traditionally, the most popular method of composting has been the open static pile (OSP) in bins, piles or windrows, managed by primary, secondary and curing stages.
More recently, in-vessel (IV) systems have become increasingly used. The most popular system is rotating drums.
Work at Michigan State University estimated the costs of the OSP and IV animal composting systems and compared them to other routine methods of managing pig mortalities.
Data for the mortality systems was obtained from two Michigan farrow-to-wean operations of 3,300 and 2,500 sows.
The OSP system used on the first farm consisted of six, 12 x 22 x 6-ft., three-sided bins with a concrete floor and a 25 x 75-ft. concrete apron in front of the bins. Compost batches were first established in two bins over a 30-day period. Employees separated carcasses of young and adult pigs to different compost batches whenever possible.
Bins with small pig carcasses were turned twice — at 30 days, then again at 60 to 90 days of composting. Piles of adult pigs were turned three times at 30 days, 60 days and then at 90 to 120 days of composting.
With the last turn, the composting material was moved to a temporary stack for future application to the fields. Bones were collected and recycled at all turns and composted until brittle.
Since the composting facility was not covered and was subject to precipitation, runoff was collected and directed to earthen manure storage.
The IV system used on the second farm was a horizontal rotating drum system that was 4 ft. in diameter and 42 ft. long.
The composter, located about 100 ft. from the hog barns, was operated on a continuous-flow basis, with mortality loaded and compost material discharged from the unit daily.
Clean, dried wood shavings and compost from a previous batch were added in proportion to the amount of mortality added, usually about one bag of shavings per 600 lb. of sow carcass.
The composter’s stainless steel, insulated drum had openings for aeration. For optimal aeration during operation, the drum was not filled past 75% of capacity.
Drum rotation varied by season, more in summer, less in winter, for an average of about 10 times/day. Consequently, retention time varied from about seven days in summer to 14 days in winter. Electrical use in summer was about twice that used in winter.
The number of revolutions and amount of moisture added were controlled by the operator and depended on the temperature of the product within the drum and appearance of the compost being discharged. Too much moisture resulted in leakage from the unit.
When exiting the IV unit, compost material was screened to separate bones from fine, carbonaceous material. The bones were reintroduced into the IV unit for further composting.
The rest of the compost was stacked in an open-sided pole building with a mono-slope roof, where it stayed for 5-6 months. It was turned periodically before being spread on cropland as a soil amendment.
When mortalities exceeded IV capacity, they were placed into a short-term OSP until mortalities returned to normal and were shifted from the short-term OSP to the IV unit.
Table 1 compares the costs of the two mortality composting systems. Based on a 15-year life for both systems, the annual cost per pound of mortality was less for the OSP system compared to the IV system.
Both farms used in this case study operated less expensively (per unit of mortality) than the Nebraska bin system, which was considered a low-investment system but actually cost more to operate.
Using the case study cost/lb. of mortality values, Michigan State researchers estimated that for a composting system that is sized, sited and operated appropriately, a 2,000-head finishing operation would generate about 20,800 lb. of mortalities annually. It would have $1,012 or $1,416 in annual costs if an OSP or IV system was used, respectively. The estimate was based on an assumption that 2.6 groups would be fed annually, mortality rate would average 2.5%, and the average dead animal weight would be 160 lb. (This estimation was done to let the contract grower know his costs as well.)
Researchers point out that costs on other farms may vary due to differences in mortality (rate and weight), differences in type of composting system and management practices.
In comparing the cost of OSP vs. IV systems, the IV system was 28.5% more expensive on a unit of mortality basis.
The costs of composting in open static piles formed in windrows or overlapping piles on a concrete pad were not considered in this study. Both approaches would likely require less facility cost and be less expensive to operate.
Incineration, rendering, on-farm burial and landfill burial are estimated to be slightly-to-significantly more expensive per unit of mortality than composting.
Moreover, convenience remains a major consideration in selecting a management system for routine mortalities on the farm. Other concerns are avoidance of aesthetic nuisance to neighbors and evaluation of cost factors, including economies of scale, management and maximizing throughput and longevity of the system.
This work was supported in part by the National Pork Board.
Researchers: Dale Rozeboom, Department of Animal Science; Gerald May, Gratiot County Extension; and Darrin Karcher, Department of Animal Science, Michigan State University. For more information, contact Rozeboom by phone (517) 355-8398, fax (517) 353-1699 or e-mail [email protected]