An Auckland central vet says backyard chicken owners need to be "lead aware".

Backyard chicken owners in Auckland need to be aware of lead-contaminated soil possibly leading to lead-contaminated chickens, a vet says.

Sandringham resident John Fowler bought two chickens to keep in his backyard just over six months ago.

He says the hens were seemingly healthy but a chance encounter with a vet, Liz Cowie, prompted him to get them tested for lead.

"It was really random, we just bought a chook feeder off Trade Me and the lady that was selling it to us said she was a vet studying lead toxicity and we should have them tested."

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The test results showed the hens had lead levels so high they were deemed unfit for consumption under western food standards.

"We are gutted because we love them, we absolutely love them, and they are just awesome animals."

Fowler says Cowie recommended they should stop eating the chickens' eggs immediately and they have now sent egg samples off for further testing.

Cowie, who works at St Lukes Pet Doctor, says it has been eye-opening the amount of sick chickens brought into the clinic which test positive for lead.

While lead does pass from the chicken into the egg, Cowie says there is limited research as to how much this is exactly.

In one specific case at St Lukes Pet Doctors the lead level in the egg was around one-third of that detected in the bloodstream of the hen.

Cowie, a Masters student, is currently researching the prevalence of elevated lead levels in backyard chickens in Auckland.

"It is too early to comment on the findings of the study but we hope that the results will let us know how widespread the issues is," she says.

Grey Lynn resident Rita Rosenberg-Smith's ex battery hens have also tested positive for high levels of lead toxicity at the St Lukes clinic.

She says she wasn't shocked by the results as one side of their villa was flaking paint, which has now been completely stripped and repainted.

"We knew the paint was very old and therefore lead. Stripping and painting was on the long list of jobs but not urgent till the results of the test."

Before the test results Rosenberg-Smith says she had never thought about the potential transfer of lead from the chooks to her family.

"I knew that lead is especially dangerous to young children so I had myself and our young daughter tested as soon as I could arrange it.

"We have thankfully no evidence of elicited lead levels in our blood," she said.

Cowie says lead-based paint from older houses is believed to be one of the main sources causing lead toxicity in chickens.

Chickens with lead toxicity often show nervous signs such as a loss of balance, inability to perch properly, loss of appetite, and in very severe cases, seizures and death.

However, chickens do not necessarily have to be showing clinical signs to have very high levels of lead in their blood, Cowie says.

In the past Cowie has had urban chickens herself. She says while they are fantastic, pets owners should be "lead aware".

Hens can be treated through chelation therapy to reduce their lead levels.This can be carried out by a number of veterinary clinics across Auckland.

Call your local vet for more information.