When animals die, it is the responsibility of the owner to dispose of their carcasses in a way not harmful to the environment or public health. This is true for farm owners, pet owners, organizations with service animals (e.g. police departments), animal shelters, and laboratories.
It is especially true for research facilities that have animals for experimentation. Even more than other facilities, labs must be scrupulous in disposing of animal bodies not just to prevent exposure to humans and the environment, but also out of concern for public perception.
Veterinarians often offer disposal service to owners of pets who have died, either at the vet’s office or elsewhere, but they are not obliged to do so.
Do not touch a diseased animal without protective clothing and gloves. If for some reason, contact without gloves has been made, wash the hands with soap or detergent. If there are signs of zoonotic disease like rabies, inform local animal health officials immediately and clean the location with chemical disinfectant to prevent the infection from spreading further.
Methods of disposing of dead animals including burial, incineration, rendering and composting.
Burial is the oldest disposal method, but it requires thoughtful selection of the burial site. The carcass should be wrapped in a plastic bag, placed in a box, and buried underground. When selecting a burial site make sure there are no nearby underground water sources or areas that may flood to reduce the chance of water contamination. Another factor to consider is the type of soil; make sure the ground does not contain too much sand. Burial is difficult in the winter in colder climates.
Burning carcasses inside a fired incinerator reduces mass and destroys pathogens. Incinerator ash is then packaged or encapsulated and sent to a landfill. Burning is usually not economical due to the high energy and labor costs and the paucity of certified and approved incinerators. Burial is usually preferable except in cases of specific diseases where state laws require disposal using incineration. Cremation, used to process human bodies, is not quite the same as incineration. Animals can be cremated, although this is more often done for vets whose owners may have a sentimental attachment to the animals.
Rendering is the process of converting dead animal bodies to pathogen-free useful byproducts such as protein for agricultural feed. Mammal carcasses are about 50 percent water and 20 percent protein. Carcasses are ground up before chemicals or steam is introduced. In a wet rendering process, steam enters the rendering tank, along with the biomass. In the dry process, steam is confined to a jacket that surrounds the tank containing the material being rendered. Even in a dry process, material in the tank contains water from the animal body. Chemicals, usually caustic, are also introduced to drive the pH up. Centrifuges, filters, and chemical treatment can be used, depending on what the operator is looking to produce as final products. Efficient rendering systems convert most of the biomass to saleable products; some unusable waste eventually goes to a landfill.
Rendering is sometimes judged as not environmentally friendly because the dead animals must be transported to remote rendering plants and there is a risk of prion disease transmission. (It is not clear if conventional rendering destroys prions.) Although the rendering unit operations destroy most prions, the process is not thought reliable enough to ensure sterilization.
Alkaline hydrolysis involves mixing the carcass with an aqueous solution of sodium hydroxide or potassium hydroxide and applying heat. Often marketed as “digesters”, these units are promoted by their makers as using less energy and producing less troublesome wastes than incinerators. They operate hotter than ambient temperature, but not nearly at the temperatures required to support combustion. Some operate at high pressure and a temperature of 230 to 250 degrees F, similar to a pressure cooker. Others operate at ambient temperature and more moderate temps of 200 degrees F. The higher temperature and pressure promote faster decomposition. Cycle times can be as low as 6 hours (time from loading unit until final removal).
The Indiana-based company Bio-Response Solutions makes units of various sizes. The effluent is promised as sterile, including free of prions (which are suspected to cause Mad Cow Disease.) The solid remains are typically less than 5 percent the weight of the animal carcass. The liquid is removed and neutralized to a lower pH. Then it can be drained to the sewer and municipal water treatment system, or, in an agricultural area, spread on the fields.
See also: Carcass disposal: A comprehensive review
This natural process allows microorganisms such as bacteria and fungi to decompose dead animals into organic matter. Composting is the preferred method on farms; it costs less as piles can be prepared readily with the equipment available on the farm. Composting of dead animals is considered a valid method by bio-security agencies in the US as the final product of composting can be used as fertilizer on fields.