Farmers and animal processors who compost mortalities now have new options, thanks to the new rules outlined in the Bodies of Dead Animals Act.

That act, which was filed by the Michigan secretary of state last fall, describes alternative and possibly less expensive composting methods. For the first time, these rules allow animal processors such as butcher shops, slaughtering facilities, taxidermists, road commissions, veterinary clinics and market collection points an opportunity to use composting to manage business animal tissue byproducts. Previously, farmers could compost their on-farm mortalities only in roofed structures with at least three sides. Processors were not allowed to compost at all.

The new rules allow four composting methods: in bins; in open piles on bare soil without floor, roof or walls; in windrows; and in large containers (in-vessel composting). With any of these methods, aeration of the compost material may be forced (mechanized with fan and ductwork), active (mechanical turning of material) or passive (air exchange within the composting material occurs as fresh air is pulled into the lower portion of the pile when heat takes gases out of the upper portion).

The two new options — open pile and windrow systems — are the first to allow composting on bare soil without a surrounding structure. These two systems decrease composting costs but are allowed only on smaller farms with no more than 20,000 pounds of animal tissue annually. In either case, open composting must be done on land used for crop production. And though collection of compost leachate is not required, the compost areas must not violate any other federal, state or local laws. The site for open composting may be used for only two years, with new additions made only in year one, and year two being allowed just to finish the composting process. An open composting site may not be reused for composting for 10 years.

So what systems may be used on larger farms? All of them could be. However, for farms with more than 20,000 pounds of mortality annually, open piles or windrows must be on an approved concrete pad or liner. On large farms, all leachate must be managed by reintroducing it into the compost pile, diverting it to a treatment system, and/or collecting and storing it in a storage facility with an approved liner.

Processors may compost using any of the systems, but like large farms, they must conduct open composting on a concrete pad or liner.

New tool helps ease decision process

These methods vary in their speed of composting, labor required, environmental risk, expense and aesthetics. All of the methods require the systematic formation, identification and management of compost batches. Spartan Compost Sizer is an Excel spreadsheet tool that determines the proper size and number of batches, whether kept in bins, open piles, windrows or larger containers. The program considers the length of time it will take to complete the composting process using animal inventory, the greatest mortality rate or death loss in any one season, average animal weight and a volume factor (also called the volume coefficient or bulking agent to animal tissue ratio in pounds per cubic foot).

For a copy of the new rules and a document explaining those rules called the Michigan Animal Tissue Compost Operational Standard, go to www.msu.edu/~rozeboom. The Spartan Compost Sizer program is also available at that site.