Most bones break down when composting animal carcasses, but a few large bones will usually remain.
With proper composting, the bones will break down over time. This may take several months for larger livestock bones and as little as 60 days for smaller carcasses such as poultry. If large bones remain in the compost pile, they can be added to additional compost piles until completely degraded.
There are many options available for disposing of livestock and poultry carcasses. Rendering is an option in areas where the service is offered, but has some limitations on the type of animals they will pick up.
Compost containing animal carcasses should probably be utilized on crops that are not meant for human consumption for a couple of different reasons.
Disposal of the end product with regard to roadkill compost…we use it on the roadsides and plant vegetation on the roadsides.
With [farm] mortality compost, we want to be careful about where we are putting cows and chickens because we are using it back on the farm. So we may want to remove the large bones [and reuse them as part of the base for the next mortality compost pile]. We do not want to puncture any tires. But the bones do get pitted and will start breaking apart after a couple of cycles of the composting process. We do not want to use this on food crops. We may prefer to use this on field crops where the soil is tilled. We can apply the compost and then till it in. Definitely use it on crops that are harvested above the ground…corn and things like that. Do not use [mortality compost] on root vegetable or on things where we risk contamination if there is a problem.
Mortality compost can also be used in forested areas.
For active decomposition of animal carcasses, compost microorganisms require a source of nitrogen (N) (dead livestock or birds), carbon (C) (straw, corn stalks, shavings, litter, etc.), oxygen, water and elevated temperatures. An ideal C:N ratio should fall between 15:1 to 35:1. Oxygen (air) can be introduced when turning the compost. If proper moisture is not supplied, the organisms cannot survive. Ideally, moisture content should range from 45-55%, or wet enough when the compost is squeezed to leave your hand feeling moist, without actually forming drops of water. When all components are present in the correct ratio, the compost pile heats naturally, destroying most pathogens while microbial activity degrades the carcasses.