Short answers, pulled from the story.
Animal welfare is the quality of life and overall well-being of animals. Animal welfare science measures it using factors such as longevity, disease, immunosuppression, behavior, physiology, and reproduction, though there is debate about which best indicate welfare.
The Five Freedoms are freedom from thirst and hunger, freedom from discomfort, freedom from pain, injury, and disease, freedom to express most normal behavior, and freedom from fear and distress. They grew out of guidelines that animals require the freedom to stand up, lie down, turn around, groom themselves, and stretch their limbs.
Animal welfare takes a utilitarian view that animals may be used if the benefits to humans outweigh the suffering, a position also called welfarism. Animal rights advocates such as Gary L. Francione and Tom Regan argue that any use of animals is unacceptable and that animals should not be regarded as property.
An animal welfare movement has been active in England since 1822, when Irish MP Richard Martin brought the Cruel Treatment of Cattle Act 1822 through Parliament. Martin helped found the world's first animal welfare organization, the Society for the Prevention of Cruelty to Animals, in 1824, which became the RSPCA after Queen Victoria gave it her blessing in 1840.
The Animal Welfare Act 2006 makes owners and keepers responsible for meeting their animals' welfare needs across pets, agriculture, entertainment, and research. Anyone who is cruel to an animal or fails to provide for its welfare needs may be banned from owning animals, fined up to 20,000 pounds, and sent to prison for up to six months.
Broiler chickens are bred to grow very large for meat, which causes a high incidence of leg deformities, lameness, and broken legs, along with heart and lung strain and a fluid buildup called ascites. In the UK alone, up to 20 million broilers each year die from the stress of catching and transport before reaching the slaughterhouse.