A knacker is a person in the trade of rendering animals that are unfit for human consumption, such as horses that can no longer work. This leads to the slang expression "knackered" meaning very tired, or "ready for the knacker’s yard", where old horses are slaughtered and made into dog food and glue. A knacker's yard or knackery is where this takes place, as opposed to a slaughterhouse, where animals are slaughtered for human food.
The term is used in this literal sense in British English and Irish English, and gained some notoriety during the outbreak of mad cow disease (BSE) in the United Kingdom. The Slaughterhouses Act 1974, the Meat (Sterilisation and Staining) Regulations 1982 and the Food Act 1984 all have a definition of a 'knacker's yard' as "any premises used in connection with the business of slaughtering, skinning or cutting up animals whose flesh is not intended for human consumption".
