The anti-vivisection movement failed to achieve federal regulations on animal experimentation and declined as medical science advanced.

[5][6] 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.

[7] 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,[8] while leading to many welfare concerns including painful skeletal problems.

[9][12] Animal experimentation also increased significantly over the course of the twentieth century, largely driven by the development of new drugs.

[14] Following public outcry over abuses of dogs reported in the media, the Animal Welfare Act was passed in 1966.

The HMSA stipulates that animals be "rendered insensible to pain...before being shackled, hoisted, thrown, cast, or cut", and sets out which methods of slaughter are appropriate for which species.

[20] In 2010 the Government Accountability Office (GAO) released a report criticizing the United States Department of Agriculture's (USDA) enforcement of the HMSA.

Those found guilty of assaulting or killing Federal inspectors responsible for such tasks also faced additional sentencing.

Basic treatment was expanded to include humane and reasonable handling of the animals, and required shelter from weather and temperature extremes, proper ventilation, adequate housing, decent sanitation, and adequate veterinary care at all stages in the animal's life.

The definition of animal was broadened to rid the law of the possible interpretation that dogs used for hunting, security, and breeding were not included in its protection.

Under this law, it was not permitted for a single animal to be used in more than one major operative experiment, from which it was also allowed adequate time to recover as guided by a veterinarian with proper training.

The act also made it a felony to trade, have knives, gaffs or other objects that aided in use of animal fighting.

[28] In 2013, "An Act to Amend the Animal Welfare Act to Modify the Definition of 'Exhibitor'," added ‘‘an owner of a common, domesticated household pet who derives less than a substantial portion of income from a nonprimary source (as determined by the Secretary) for exhibiting an animal that exclusively resides at the residence of the pet owner,’’ after ‘‘stores,’’ in section 2(h).

[32] This table shows which states have enacted bans on various industrial farming practices considered to be inhumane.

[35] In 2013, American meat consumption was second-highest among Organisation for Economic Co-operation and Development (OECD) countries (behind Australia) at 200.6 lbs per capita annually.

[37] According to a 2009 Food and Agriculture Organization (FAO), American egg consumption was higher than the developed countries’ average.

[42] While these poll numbers do not indicate an increase in vegetarianism and veganism, plant-based diets and the consumption of fewer animal products seem to be a growing trend.

[51] Each local IACUC reviews research protocols and conducts evaluations of the institution's animal care and use which includes the results of inspections of facilities that are required by law.

The Public Health Service (PHS) Policy and Animal Welfare Regulations (AWRs) state that procedures that cause more than momentary or slight pain or distress should be performed with appropriate sedation, analgesia, or anesthesia.

[59] In September 2016, the United States Department of Agriculture released a report on an investigation into the material covered by the Times article, and recommended that the USDA "establish adequate policies, procedures, and processes related to oversight of animal welfare at USMARC.

[64] Following major public backlash prompted by the 2013 film Blackfish, SeaWorld announced in 2015-16 that it will end its controversial orca shows and breeding program.

[23] The Animal Fighting Prohibition Reinforcement Act provided for felony-level penalties including multi-year prison sentences and large fines for each offence.

[23] Passage of this law was followed by the involvement of the Inspector General's Office of the U.S. Department of Agriculture in ongoing investigations around the United States.

In addition to the controversial treatment a dog receives when he has potential as a fighter, according to a filing in U.S. District Court in Richmond by Federal investigators in Virginia, which was obtained under the Freedom of Information Act and published by The Baltimore Sun on July 6, 2007, a losing dog or one whose potential is considered unacceptable faces "being put to death by drowning, strangulation, hanging, gun shot, electrocution or some other method".

Protests were first raised in the 1870s, and, in the middle twentieth century, laws were enacted to curb events using animals.

The PRCA (which governs about a third of the rodeos conducted in the United States annually) has provided rules for its members regarding animal welfare.

Some local jurisdictions have banned the use of certain rodeo tack or certain events such as tie down roping or steer tripping.

[citation needed] A 2015 Gallup poll found that 32% of Americans agreed that animals should have the ”same rights as people”, up from 25% in 2008.

[77] The HSUS has been instrumental in the passage of several state-level bans on cruel farming practices,[33] and Mercy for Animals' ongoing (as of April 2016) corporate cage-free egg campaign has helped bring about a number of corporate pledges to use cage-free eggs.

In 2013 the NhRP filed the first-ever lawsuits on behalf of chimpanzees, demanding courts grant them the right to bodily liberty via a writ of habeas corpus.