Emergency Livestock Disposal Home

Project Executive Summary

Project in Detail

• Background
• Objectives
• Composting System Tested
• Research Methods
  • Construction
  • System Performance
  • Cover Material
  • Air Quality
  • Water Quality
  • Biosecurity
• Preliminary Results
• Project Sponsors & Contacts

Draft Guidelines for Emergency Cattle Mortality Composting

RESEARCH  METHODS

Biosecurity

One of the most crucial questions regarding use of composting for disposal of diseased animals is whether disease-causing bacteria, viruses, and parasites will continue to pose a threat.

Two separate biosecurity issues must be studied to determine if composting can safely dispose of carcasses that are infected with a contagious disease.

• Are pathogens (infectious bacteria or viruses) reliably contained within the composting pile? and

• Are the environmental conditions (heat, toxic gases, drying, microbial competition) inside the composting pile capable of killing or inactivating pathogens?

Two types of data are being collected to answer the containment and inactivation questions.

Pathogen Inactivation

To evaluate pathogen inactivation vaccine strains of two poultry viruses are placed inside the composting piles in retrievable containers.  A commercially-licensed vaccine strain of avian encephalomyelitis (AE) virus is used to emulate foot-and-mouth (FMD) virus. Like FMD virus, AE virus is categorized in the family picornaviridae, which are very small, single-stranded, RNA type, non-enveloped viruses that are very stable in a variety of environmental conditions.

A commercially licensed (B1Lasota) vaccine strain of Newcastle disease virus (NDV) also is used to evaluate the potential biosecurity of the composting process.  NDV is a single-stranded RNA enveloped virus that is highly representative of other viruses, such as influenza viruses, that commonly threaten animal populations.

Two types of retrievable containers are used to insert test viruses into and remove them from the composting test units.  Cryogenic vials (shown below) are used to expose the viruses to the heat of composting while simultaneously isolating them from other environmental stresses such as toxic gases, changes in pH, drying, etc.   

To evaluate the effects of previously mentioned stress factors besides heat, viruses are placed in dialysis cassettes like the ones shown here.  Cassettes, which look much like a photographic slide, consist of two cellophane-like gas-permeable membranes affixed to a plastic frame.  Viruses, in solution, are injected into the space between the membranes. 

To insure that the cassettes and viruses are exposed to the same environmental conditions present within the compost, the cassettes are gently packed in cover material (below) before being inserted into the compost pile through access tubes installed near the carcasses at the time the test units are constructed. 

Pathogen Containment

To determine if pathogens are contained within the composting process, the surfaces of the cattle carcasses and surrounding cover material are purposely contaminated with the vaccine strains of NDV and AE virus.  This is done by inoculating and propagating viruses inside chicken eggs, and then distributing the eggs (and their contents) throughout the composting test piles before the cover material is added.

To determine if viruses escape from the composting operation via wind, insects, or other means, specific pathogen free (SPF) sentinel chickens are stationed in cages located 10 feet from all sides of the composting test units (during spring or summer trials only).   

Weekly blood samples are collected from the sentinel poultry for a period of 10-12 weeks after test units are constructed.  Bloods samples are subjected to hemagglutination-inhibition (HI) tests to detect an immune (antibody) response to NDV, and Enzyme-Linked Immunosorbent Assay (ELISA) to detect antibodies to the AE virus.

In Brief

-  The potential for farm-scale cattle composting operations to kill viruses is being evaluated by placing samples of two types of avian vaccine viruses into the composting pile, and testing the viability of samples that are retrieved from the pile during the initial weeks of the composting process.

- The ability of emergency composting systems to retain potentially  harmful viruses is being tested by placing caged pathogen-free poultry in the vicinity of the composting test units (summer trials only) and testing weekly blood samples drawn from the birds for evidence of an immune response to vaccine viruses placed in the composting windrows.