All that was left of a cow after 6 months composting in sawdust.
Carcass disposal may have adverse environmental impacts, particularly on the quality of water and air.
Environment Canterbury’s Proposed Natural Resources Regional Plan includes the following permitted activity rules, WQL23, AQL32, AQL67 and AQL63 which apply to the disposal of dead animals and offal. Provided that you can comply with all the conditions of these rules then disposal of carcasses and offal, from animals that die or are killed on your farm, to offal pits, by composting or burial is permitted. If for any reason you cannot comply with all the conditions, you will require a resource consent.
Depending on your location there may also be other plans or rules you need to consider. Call Environment Canterbury for full details to check which rules apply to you.
Composting of dead stock offers an alternative to traditional disposal methods and decreases the risk of groundwater contamination. A well-managed composting system can be low cost, environmentally sound, and virtually odour-free. Composting involves layering dead animals within a bulking agent such as sawdust or straw.
Once complete, compost can be spread over nonproductive areas (domestic gardens, shelter belts, woodlots) or can be used for part of the bulking agent in a new composting pile. Compost should not be spread on ground where animals will graze as there is a risk of pathogens being present in the compost.
The carbon to nitrogen (C:N) ratio of composting material should be at least 5:1. Since animal carcasses are high in nitrogen, the bulking agent needs to be high in carbon. The process must be aerobic if odour is to be minimised, so air penetration through the compost heap is essential. A bulking agent with material size 12-44 mm in diameter will allow better airflow through the pile. Materials must be able to settle around and be in contact with the carcass.
Untreated sawdust is recommended because of its small particle size and high absorbency that minimises leachate. Straw can be used but there are problems in using it such as longer breakdown times, and leachate
production. Generally a straw stack will need to be roofed and built on a concrete surface so that leachate
can be collected. You can also use finished compost as part of the bulking agent in a new pile - a rule of thumb is 50 per cent old-to-new, but you may want to use more or less depending on how degraded the bulking agent is in the finished compost.
Composting can be undertaken in bins or open windrows.
Sheep composting windrow.
A sheep composting bin made of 50 x 150 mm treated timber.
Where possible, arrange for carcasses to be picked up by a licensed dead stock collection service. Operators skin the dead animals and render the carcass to produce protein meals, tallow and fertiliser.
Dead animals should be carefully handled to avoid damaging their skins as their value is greatly diminished if they are dragged or ripped. The collection point should not be visible from the road.
While offal pits are considered a simple and cheap method of disposing of small quantities of dead stock, they require good management in order to reduce their impact on the environment.
Example of a well-constructed offal pit.
Shallow burial may be a convenient method of disposal where water tables are low enough to avoid groundwater contamination. Controlling vermin and scavengers can be difficult. Make sure that the hole is backfilled immediately and that the buried carcass is well covered, so that dogs or other scavengers cannot dig it up. Select an area with clay or impervious soil below to contain any leachate and site the hole at least 100 m from domestic bores or surface waterways to avoid contamination. Do not bury animals in the floodplain of a waterway.
For more information, contact Environment Canterbury Customer Services in Christchurch or Timaru.
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Natural Resources Regional Plan
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