California Governor Jerry Brown (D) has signed legislation (S.B. 27) that prohibits administration of a “medically important antimicrobial drug to livestock solely for purposes of promoting weight gain or improving feed efficiency” as of January 1, 2018.

Under the statute, antibiotics may be used only when ordered by a licensed veterinarian through a prescription or veterinary feed directive.

“The science is clear that the overuse of antibiotics in livestock has contributed to the spread of antibiotic resistance and the undermining of decades of life-saving advances in medicine,” Brown said. See Signing Message of Governor Edmund G. Brown Jr., October 10, 2015.