On Wednesday, Burger King Corp. became the world's first fast-food chain to get all of its eggs and pork from cage-free chickens and pigs.

By 2017, the world's second-biggest fast-food restaurant business will cater to customers who seek more humanely produced fare.

The move is said to make better living conditions for tens of thousands of animals, according to Wayne Pacelle, president of the Humane Society of the United States, which has been pushing Burger King and other corporations to consider animal welfare in purchasing policies.

Numerically this is significant because Burger King is such a big purchaser of these products, he added.

Burger King, which uses hundreds of millions of eggs and tens of millions of pounds of pork annually, made the decision in a game-changing fashion, as a huge new market has opened up for humanely raised meat. Already 9 percent of the company's eggs and 20 percent of its pork are cage-free.

As the transition will take about five years to complete, the cage-free eggs will be instrumental in helping the company serve breakfast sandwiches and burritos at its 7,200 restaurants across the U.S., the company said.

While other restaurant companies have incorporated some cage-free egg purchases in their supply systems, the Burger King announcement marks the first time a major chain has made a commitment to phase out all egg-buying from caged hens, according to Matthew Prescott, a spokesman for the Humane Society of the U.S.

The whopper-sized move comes after demands by restaurant chains to have their egg suppliers increase cage sizes for laying hens. But to the restaurants' surprise, bad publicity for the suppliers brought on by the demands resulted in a change in industry standards.

Farms now have the option to switch to cage-free production, but it's not an overnight process, Gene Gregory, chief executive of the farm group United Egg Producers, told the Associated Press

New production facilities have to be built or existing ones have to be converted, he said, and producers generally don't make the change until they are contracted to do so by buyers because of the expense involved.

It costs an extra 25 cents to 40 cents per dozen to produce cage-free eggs, Gregory said

And while American farmers produce about 250 billion eggs per year, only a small percentage of those come from uncaged hens, according to a report by the Wall Street Journal.

Of the 10.5 million laying hens in 2010, only about 4 percent weren't in cages.

Our attitude is our producers believe in consumer choice and if that's what their consumers want to buy, they'll produce cage-free eggs for the marketplace provided the customer is willing to pay the additional cost, Gregory said.