A British animal protection agency launched a campaign on Friday to draw attention to the plight of broiler chickens - birds bred for their meat.
The fowl that provides Britain's favourite meat suffers from heart failure, leg pain, ammonia burns and skin infections before reaching retailers' shelves, The Royal Society for the Prevention of Cruelty to Animals (RSPCA) said.
"Broiler chickens typically end up having considerably less space than an A4 piece of paper to move around in, yet many consumers are unaware of the misery commonly endured by broilers," said Caroline Le Sueur, the society's senior scientific officer.
Broiler chickens generally grow four times faster than egg-laying hens, until the end of their commercial lives after six weeks. To maximise growth, birds routinely receive just one hour of darkness a day, Le Sueur said.
The majority of Britain's 820 million broilers grow up in squalid conditions, she said. Free-range broiler chickens are healthier and suffer less.
The society, which is the world's oldest animal protection agency and was once supported by Queen Victoria, urged consumers to pressure supermarkets into demanding improved living standards from chicken suppliers.
"The role of the consumer cannot be overstated," Le Sueur said. "Shoppers can influence animal welfare standards by the food they choose and the pressure they put on retailers to demand an end to systematic cruelty."
The society said it hoped the government would one day introduce legislation governing how meat chickens could be reared.
A spokeswoman for the Department of Environment, Food & Rural Affairs said the agency shared the society's welfare concerns.
She said the government had sponsored a research project on stocking density that would conclude in March 2003.
"The UK wants to see swift EU action on broilers," she said. "Spending on research into broiler welfare will rise from 300,000 to 400,000 pounds (482,000 euros to 643,000euros) next year when a new project looking at leg health comes on stream," she said.