Slaughterhouse wastes and dead animals are used to prepare meat and bone meal. Slaughterhouse wastes consist of portions of animals that are not suitable for human consumption, such as carcass trimmings, condemned carcasses, condemned livers, inedible offal (lungs) and bones. Normally hair, hooves and blood are not included. After animals have died their carcasses can be rendered to destroy disease organisms and made also into meat and bone meal.

There can be a wide variation between plants and batches in what goes into the meat and bone meal that is being prepared. If the ash content is high, this indicates that it contains a higher amount of bones and is referred to as meat and bone meal. If the ash content is lower it is referred to as meat meal. Typically when the phosphorus content is above 4.5 % P, then it is called meat and bone meal and when it is below that level it is referred to as meat meal or some other term.