Oliver’s company sources a fast-growing breed of chicken from a farm that feeds the birds a low-energy diet, a combination the RSPCA says it is concerned about.
The farm which is not part of the RSPCA's Assured scheme, has claimed a local inspector from the charity has approved the birds’ welfare.
The RSPCA was unable to confirm this, but made it clear that a visit from an inspector was not a stamp of approval about a premises.
Jamie Oliver has long won praise for his campaigning against cheap meat from intensively reared animals on factory farms, which provides little nutritional value.
Last year the celebrity restaurateur received an RSPCA gold award – the highest level possible – for his work to improve farm animal welfare and championing higher welfare food.
The Jamie’s Italian Restaurants group website states that all its chicken is from Creedy Carver, a free-range Devon farm where the birds have room to move and fresh grass.
The head of Creedy Carver says his chickens are healthy because they have the freedom to roam outdoors and eat all they want.
However, in common with 95 per cent of chickens slaughtered for meat in the UK, the breed used is one that over decades has been modified to be capable of growing unnaturally quickly.
Animal welfare experts have long criticised the almost universal use of fast-growing breeds because rapid weight gain causes organ failure and painful broken bones when a bird’s legs cannot support its body mass.
But at Creedy Carver the chickens are fed a low-energy diet so they do not grow as fast as in factory farms.
However, an RSPCA expert said this combination can potentially cause problems as these breeds need diets that match their predisposition.
Senior scientific officer Kate Parkes said: “It’s a risk factor if you have faster growing breeds that are genetically predisposed to rapid weight gain – its diet needs to accommodate that. They could be hungry. It could be like feeding a growing child a suboptimal diet.”
The RSPCA’s guidelines on welfare for meat chickens say the charity has concerns over the practice of adjusting broilers’ diets to slow their growth rates.
The charity’s welfare standards state: “The RSPCA is concerned about the practice of deliberately slowing the growth rate of fast-growing broilers by adjusting either the quality or quantity of their feed to delay the time taken to reach slaughter weight, as can be the case when rearing fast-growing broilers in free-range systems.
“Broilers should be fed a diet that allows them to achieve their genetic growth rate potential.”
The RSPCA and other charities are lobbying supermarkets and food giants across the UK to switch to slow-growing birds.
Creedy is free-range but uses a “genetically standard” fast-growing bird, which is not permitted under the RSPCA’s farm-assurance scheme.
Earlier this year the RSPCA said the vast majority of the chickens bred for meat in the UK were kept in conditions that “cause substantial suffering”.
Hannah Yates of animal welfare campaign group Humane League said: “Switching to slower-growing breeds would eliminate the risk of these issues so why are restaurants still lagging behind on this?”
James Coleman, director of Creedy Carver, said his birds’ feed was never restricted, and that if they were hungry they would eat all the time – but they don’t.
He said the farm was not using the birds’ full potential to grow large very quickly, and compared his chickens’ lifestyle to that of a person eating a healthy diet and exercising freely, in contrast with factory-farmed birds that were more like a person eating junk food and not moving.
“If you’re healthy and active outdoors, you naturally eat less, but if you’re cooped up indoors you eat out of boredom – and it’s true for birds,” he added.
Being free-range means the chickens can peck, forage and explore at will.
“Their low-energy diet was formulated by nutritionists from the mill where I buy the feed,” he said. “It’s all natural and doesn’t contain growth-promoters. We don’t have a problem with white muscle disease, which can be seen in chickens growing excessively fast.”
The farm tried using a slower growing breed but customers complained the meat was tougher, Mr Coleman said, and many restaurants had stopped buying free-range meat to save money.
“Jamie Oliver should be applauded for sticking with free-range standards when others aren’t,” he added.
An RSPCA official had inspected his ducks and seen his chickens and was happy with their welfare.
“This criticism is misguided and unfair,” he added. “Any criticism should be of intensive farming, not free-range farms.”
A spokeswoman for the Jamie Oliver group declined to comment.
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