NEW YORK — How do you measure a chicken's happiness? Is it in the way it runs for food? How much time it spends preening?

To size up what might make chickens happy in their brief lives, researchers at the University of Guelph in Ontario, Canada, are putting 16 breeds through physical fitness and behavioral tests. They're watching how well birds scramble over a barrier for food, how skittish they seem and whether they play with a fake worm.

Chickens can't say how they feel, but playing with a fake worm may be a sign of happiness.

"We have to infer when an animal is happy or content or experiencing pleasure based on their behavior," said Stephanie Torrey, one of the researchers.

In recent years, the animal welfare world has moved beyond looking at how to minimize suffering to exploring whether animals can also enjoy their lives, Torrey said.

Such measures may be considered irrelevant by companies but underscore a broader lack of consensus around the welfare of chickens, which are sometimes slaughtered as soon as five weeks after hatching.

Animal welfare advocates say cruelty begins with birds that have been bred to have breasts so big they can barely walk. They say today's chickens are genetic monstrosities crippled by pain and that the industry needs to switch breeds.

Many in the industry say there's no problem and that chickens may not move around a lot because they're sedentary. Even if they were to agree to change breeds, it's not clear what the alternatives should look like.

The two sides disagree about the cause and frequency of health issues among broilers chickens. Tyson and Sanderson Farms, for example, acknowledge that chicken breasts have ballooned over the years, but they say they're not seeing widespread problems as a result.