An advisory animal welfare agency has rejected criticism about a move to phase out battery cages for laying hens.
The National Animal Welfare Advisory Committee provides independent animal welfare advice to the Ministry of Primary Industries.
Under the new code farmers have 10 years to swap battery cages for larger colony cages.
The SPCA and SAFE, an animal advocacy group, want all cages banned.
But commission chair John Hellstrom said colony cages are a significant step up from battery and are superior to barns because they generate less dust and ammonia and stop chickens attacking each other.
Dr Hellstrom said it is also unrealistic to force farmers to change faster because they need time to get resource consents and bank loans.