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Emergency Livestock Disposal Home
Project Executive Summary
Project in Detail
Draft Guidelines for Emergency Cattle
Mortality Composting
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PRELIMINARY RESULTS
Decomposition
Temporary Excavation
Although test units in this research are not turned (to simulate biosecurity practices that would be followed in the event of an animal disease emergency), and some of the emergency cover materials that are tested have very low initial moisture content, decomposition of 1,000 lb cattle carcasses has been surprisingly rapid for all cover materials tested with the exception of the yard waste compost.
Internal temperatures in silage test units are typically 10-30 °C higher than in piles constructed with ground cornstalks, leaves, or straw/manure. Despite these substantial temperature differences, however, the extent of carcass decomposition observed during temporary excavation of test units constructed with ground cornstalks, silage, or straw & manure
has not differed noticeably.
Carcass decomposition rates are noticeably affected by seasonal temperatures. The two photos below show examples of skeletal remains after 105 days of composting that was begun during warm weather (late August). The upper photo shows a large vertebrae bone taken from a cornstalk composting test unit, and the lower photo shows a leg bone from a silage test unit. In both cases a 1,000 lb carcass were reduced to little more than skeletal remains in only 3 1/2 months.
Similar excavation of cornstalk and silage test units begun during much colder weather in November of 2002 revealed far less complete carcass decay even though the test units had been composting for nearly 5 1/2 months.
Similar decomposition rates in the cornstalk and silage test units, despite substantial differences in internal temperatures, show that higher internal temperatures, by themselves, do not necessarily indicate more rapid carcass decomposition. Internal temperatures reflect the combined effects of microbial heat production AND the ability of the cover material to retain that heat. As a result, highly permeable materials, like cornstalks, that have less ability to retain heat, may exhibit lower operating temperatures while supporting relatively good decomposition.
Final Excavation
In early September of 2003 (approximately 12 and 10 months following their construction) trial #'s 1 and 2 were decommissioned, photographed, sampled for nutrient content, and spread on cropland near the research site.
In line with the limited observations obtained during temporary excavation, carcass remains in cornstalk and silage test units were free of soft tissues, and clean dry bones were essentially all that remained. Little if any objectionable odor was noted during excavation.
Further confirming earlier observations, carcass decay in the two test units constructed from the very soil-like yard waste compost, was highly variable. Near the outer edges of the pile soft tissue decay appeared to be complete, and the remains consisted largely of clean bones. Toward the core and bottom of these piles, however, decay was very incomplete and highly odorous. Since these remains were not ready for spreading, they were mixed with ground cornstalks and placed in a new windrow for further composting.
Based on the relatively high internal temperatures observed in the yard waste compost, the poor decay in this material is believed to have been caused largely by its fine soil-like texture and relatively low permeability. This particular yard waste compost is much finer than many, and these results should not be construed to be representative of the likely performance of all composted yard wastes.
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In Brief
1. Decomposition of 1,000 lb cattle carcasses constructed with cornstalks or silage appears to be complete in 10 months or less.
2. Despite substantial differences in internal temperatures, decomposition rates appear to be nearly the same in cornstalk and silage test units.
3. Decomposition within the fine textured yard waste compost used in the first two trials was highly variable and unacceptably slow.
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