There is no best way to dispose of swine mortality carcasses. While some methods may work well for managing routine mortalities, due to capacity issues, they may not adapt to times when catastrophic mortalities occur. The optimum system for any particular farm location is based on a number of criteria, including the current state of the protein/oil market, the biosecurity required, the distance to processing sites, the local public's perception, the government regulations that apply to that location, the environmental conditions, and the ability of the farm to carry out the different procedures.
The death losses at a farm can be classified broadly as one of two types: routine or catastrophic mortalities. Routine mortalities represent a small proportion of the herd and occur throughout normal production. Catastrophic mortality events involve high death losses within a distinct time. Four predominant methods of routine swine mortality disposal are burial, incineration, rendering, and compositing. Catastrophic losses present unique challenges because of handling large amounts carcasses within a short time (and if losses are due to disease, a higher biosecurity risk).
Burial can occur either on site or via transport of carcasses to approved landfills. Typically, on-farm burial of routine mortalities is performed using a trench method, which involves excavating a narrow and shallow trench, placing a single layer of carcasses in the trench and then covering with soil. Pigs slowly decompose until they are unrecognizable, generally after a few years. One concern is that burial can have negative environmental impacts if the sites are not selected carefully. In particular, depth to groundwater or sanding soils where leachate transport to groundwater is more likely. This method is not available when the ground is frozen and predators can uncover carcasses not buried deep enough. Typically, for routine management of mortalities, this method is often reserved for smaller operations.
In terms of catastrophic mortality, disposal burial is more common. With emergency disposal burial, the number of carcasses placed in a location is typically greater, increasing the potential for leachate, making location selection critical. The use of modern engineered landfilled equipped with leachate collection and treatment significantly reduces the risk of leachate concerns. The utilization of the landfill relies on the owner’s copperation and the transport of carcasses. Efforts to support bio-secure transport are required in cases where mortality is from a transmittable disease.
If mass burial is required on site, the combination of topographic, geologic, soil, and water resource data should be used to identify and map burials sites. Farms should work to identify locations for on-farm burial as part of emergency preparedness plans.
Shallow burial is a bit different, almost a cross between composting and burial. Often burial decomposition is slowed by lower oxygen concentrations and the fear of leachate movement. Shallow burial tries to address this by leaving the carcass near the surface.
The process is something like this – dig a long narrow trench approximately 20-inches deep by the width of an animal body for the length you need. You’ll want to put in a layer of organic material, like wood chips, approximately 12-inches thick. This absorbent material will help absorb any potential leachate from the animals and also can help facilitate air exchange and keep the zone aerobic.
The next step is to get the animals in the trench, one layer thick. The animals are probably mostly even with the ground. What we are trying to do with this approach is keep them in an area with high soil microbial activity to help promote decomposition. At this point, put the removed soil back on top, plant grass or perennial vegetation to keep it in place, and let nature help with the circle of life.
It will take a little time, but most work has shown in about a year, the animal’s decomposition will be nearing completion.
If you are looking into what you might need to get started on the process Michigan State has a spreadsheet to help you plan sizes and material needs. https://www.canr.msu.edu/resources/spartan-emergency-animal-tissue-composting-planner-v1-04.