Proposition 204, the Humane Treatment for Farm Animals Act, was supported by animal activist groups such as the Humane Society of the US (HSUS) and Farm Sanctuary.
The legislation makes it a crime to confine a pig during pregnancy if this prevents the animal from lying down and extending its limbs fully or turning around freely.
The crime can be punished with fines up to $20,000 and six months in prison. The initiative will take effect as of December 31, 2012.
Arizona is the second US state to have prohibited the use of gestation crates. A similar measure was approved in Florida in 2002. California is said to be the next state welfare activists will turn to.
The result is a blow for US agriculture secretary Mike Johanns, who spoke out in support of the current housing practices. In his view the common size of gestation crates provides sows with protection while maintaining clean food and water.
The National Pork Producers Council (NPPC) is worried that the result may hamper local livestock growers – and perhaps spread to other states and the 2007 Farm Bill.
“We are disappointed that the voters of Arizona adopted a proposition outlawing a husbandry practice deemed appropriate by decades of farmer experience, as well as by university researchers and the nation’s leading veterinary association,” said Joy Philippi, NPPC president.