Emergency Livestock Disposal Home

Project Executive Summary

Project in Detail

• Background
• Objectives
• Composting System Tested
• Research Methods
• Preliminary Results
• Construction & Maintenance
• Temperature
• Oxygen
• Decomposition
• Cover Materials
• Air quality
• Water quality
• Biosecurity
• Project Sponsors & Contacts

Draft Guidelines for Emergency Cattle Mortality Composting

PRELIMINARY RESULTS


Cover Material Characteristics

Lab Tests Agree with Field Performance

A wide variety of acceptable cover materials to choose from makes composting a more reliable emergency disposal option.  But, extensive field testing of more than 2-3 cover materials would be very time consuming and costly.

Preliminary laboratory testing of three cover materials that have been tested in the field, however, suggests that certain lab tests may prove very useful in predicting and ranking the likely performance of alternative cover materials.   The table below displays selected characteristics of the three cover materials originally chosen for field testing. 

In terms of carcass decay rate, two of these materials (ground cornstalks, silage) have performed well, while one (yard waste compost) performed much worse (after two field trials, this material has been replaced with other alternatives).  

Preliminary laboratory tests show that the particular yard waste compost that was field tested has gas permeability that is less than 8% of that for the silage, and less than 1.4% of that for ground cornstalks.  Extremely slow carcass decay, and a strong anaerobic odor (see Decomposition section) at the time the yard waste compost trials were decommissioned, suggest that the performance of this material was constrained by it's inability to transport O₂ into the pile, and decomposition gases out. 

The data tabulated above also appear to explain some of the similarities and differences in the field performance of silage and cornstalk test units.  The ground cornstalks have much higher permeability than the silage.  As such, the cornstalks permit atmospheric O₂ concentrations at the core of the pile as demonstrated by the preliminary results reported for Oxygen.  A potential drawback of high permeability, however, is that excessive air movement through the pile can lead to significant heat loss during cool weather.  Excessive air movement also can lead to moisture loss and low microbial activity in portions of the pile that are not near to the wet carcasses.  Similarly, high C:N ratios in the cornstalks are further inhibit microbial activity except at those locations wetted by nitrogenous liquid decay products from the carcasses. 

Good overall performance by the silage test units seem to be substantiated by a preponderance of favorable lab test results.  Gas permeability is moderate, but perhaps so high as to encourage significant heat loss.  The initial moisture content is nearly optimal for rapid establishment of high microbial activity, and a very favorable C:N ratio and substantial volatile solids content provide a microbial food source throughout the pile, not just at locations near to the carcasses.

At first glance, the respiration rates reported above seem to suggest that ground cornstalks are more degradable than the silage.  The respiration tests, however, are conducted after the materials have been pre-saturated with water.  As such, these results indicate good potential for cornstalk degradability in those areas of the pile that have been wetted by carcass liquids, but are not indicative of degradation that would occur in the preponderance of the pile that is very dry.

Laboratory testing of alternative potential cover materials such as soybean straw, oat straw, wheat straw, leaf mulch, and wood shavings, are currently underway as are thermal tests of the materials listed above. 

In Brief

1. Preliminary lab tests of the cover materials used in field trials show good agreement between lab results and field performance.

2.  Rapid development of high temperatures throughout the silage trials (desirable for rapid inactivation of pathogens) appear to be predicted by favorable initial moisture content and C:N ratios, and moderate gas permeability that permits adequate oxygen penetration while limiting pile chilling during cold weather.