Mich. Comp. Laws § 287.823: Identification of feeder pigs.

Sec. 23.

Feeder pigs shall be identified in a manner as described in subsection (2) in a manner that allows tracing to the herd of origin for the purpose of epidemiology and investigations to determine the spread of disease.

Feeder pigs shall be identified before leaving the herd of origin with official identification that contains the herd number assigned to that herd by the director unless any of the following occur:

They are consigned to a swine market or assembly point where they are identified by official ear tags which identify the market with a United States department of agriculture, animal and plant health inspection service, veterinary services prefix and a 4-digit number that allows tracing to the herd of origin by records maintained at the swine market or assembly point.

They are sold to an approved pseudorabies quarantined feedlot where they are identified on entry in accordance with this act and rules promulgated pursuant to this act, and records are maintained that allow tracing to the herd of origin.

They are sold to a broker who identifies the pigs by official ear tags which identify the broker with a United States department of agriculture, animal and plant health inspection service, veterinary services prefix and 4-digit number that allows tracing to the herd of origin by records maintained by the broker.