Animal welfare in the United States relates to the treatment of non-human animals in fields such as agriculture, hunting, medical testing and the domestic ownership of animals. It is distinct from animal conservation. History 1641–1900 The first known animal welfare laws in North America were regulations against "Tirranny or Crueltie" toward domestic animals included in the 1641 Massachusetts Body of Liberties. Starting in the late 1820s, a number of states passed anti-cruelty statutes. Many of these exempted animals used in experiments, and only twice were they invoked on behalf of animals. The first Humane Societies and Societies for the Protection of Animals (SPCAs) were formed starting in the late 1860s to run animal shelters and promote the enforcement of animal cruelty laws. The American anti-vivisection movement began in response to the opening of the first animal laboratories in the 1860s and 70s. The American Anti-Vivisection Society was formed in Philadelphia in 1883. The anti-vivisection movement failed to achieve federal regulations on animal experimentation and declined as medical science advanced. 1900–present The beginning of intensive animal farming is traceable to 1923 in the Delmarva Peninsula, where Celia Steele raised her first flock of chickens for meat. Starting in the 1940s, intensive confinement and genetic selection of chickens for characteristics like growth rate, weight, and feed conversion efficiency allowed farmers to obtain chicken meat much more efficiently, while leading to many welfare concerns including painful skeletal problems. Pigs and cows were raised in industrial farming operations starting in the 1960s. Largely due to the efficiencies brought by industrial animal farming, American meat consumption (and therefore the number of animals in industrial farming facilities) rose dramatically beginning in the 1940s. Animal experimentation also increased significantly over the course of the twentieth century, largely driven by the development of new drugs. Following the decline of the anti-vivisection movement in the early-twentieth century, animal welfare and rights movements did not re-emerge until the 1950s. In 1955, the Society for Animal Protective Legislation (SAPL) was founded to lobby for humane slaughter legislation, and the Humane Methods of Slaughter Act (HMSA) was passed in 1958. Following public outcry over abuses of dogs reported in the media, the Animal Welfare Act was passed in 1966. The animal welfare and rights movements grew in the 1970s with the publication of philosopher Peter Singer's influential Animal Liberation, and Henry Spira's successful and highly publicized campaigns against animal testing. The movements