A Ministry for Primary Industries report released this week says lameness is the single most important welfare issue in the broiler chicken industry.
The report is based on a survey done two years ago when the ministry inspected 20 of the chicken farms run by New Zealand's three main producers: Brink's Chicken, Inghams Enterprises and Tegel Foods.
It revealed that about one in three chickens being raised for their meat have difficulty walking.
It found the birds are now raised in higher densities than they were when the previous survey was done eight years ago, and they grow faster too.
The ministry says while chicken leg health on average hasn't significantly changed since 2005, older and heavier birds have poorer leg health.
An ambassador for the Compassion in World Farming society, Joyce D'Silva, says modern chicken farming means the birds grow too fast for their legs to support them.
She says the chickens tend to go lame at quite an early age because their bodies have been bred to grow so fast to increase profitability.
The Green Party has condemned the suffering described in the ministry report.
