P.L. 89-544 (August 24, 1966) was enacted to curb the theft and mistreatment of dogs and cats for experimental and research purposes. The principal federal animal protection law, it has been amended several times to address specific concerns such as the shipping of pets on public transportation, dog fighting, and using other warm-blooded animals in biomedical experiments. Although administered by the Animal and Plant Health Inspection Service, the law has always excluded farm animals from its coverage. Generally, USDA is authorized to "promulgate standards to govern the humane handling, care, treatment, and practices in experimental procedures to ensure that animal pain and distress are minimized...." The law excludes from the definition of animal "...horses not used for research purposes and other farm animals, such as, but not limited to livestock or poultry, used or intended for use as food or fiber, or livestock or poultry used or intended for use for improving animal nutrition, breeding, management, or production efficiency, or for improving the quality of food or fiber." Animal welfare has become more controversial in recent years as certain animal protection groups have argued for more extensive legal protections for animals. Some groups believe that any human uses of animals are inhumane, unethical and/or immoral, and should be prohibited. Among those who accept the premise that humans should and will use animals for food and other necessities, the debate over the meaning of animal welfare revolves around the most appropriate methods for taking care of animals, including farm animals. For example, legislation has been proposed (but not enacted) in recent years that would intervene in animal production operations by regulating confinement facilities; determining the diets of veal calves; specifying how poultry must be slaughtered; and prohibiting dealers from handling nonambulatory (downer) livestock unless they are humanely killed.