Unwanted greyhounds are being drained of their blood and then euthanised to help with the treatment of others, in the latest disturbing claims to hit the sport.

Last month, 7.30 exposed widespread doping and allegations of animal cruelty within the greyhound racing industry.

It provoked a strong response from veterinary nurses, who say they are being forced to kill some of the 17,000 healthy dogs believed to be discarded by the industry each year.

The multi-billion-dollar sport relies on massive over-breeding. Each year thousands of dogs never make it to the track because they fail to chase or simply aren't fast enough.

They're what the industry calls wastage.

Vet nurse Victoria Luxton-Bain worked at a vet clinic near Melbourne's Sandown track. She saw both ends of the greyhound life cycle, helping with artificial inseminations and euthanising healthy dogs.

"I still remember the first time I had to do it and I couldn't stop crying," she said.

"My worst day was we had seven brought in by one person and you just had to do seven, one after the other.

"When you're euthanising these dogs, they're not old dogs, they're completely healthy, and most of them are still standing there wagging their tails and licking your face while you're actually euthanising them."

Ms Luxton-Bain quit in protest and moved to an animal emergency centre, but her new job was even more confronting.

Almost weekly she was required to help drain greyhounds of their blood before they were put down.

"The blood was used for any dogs that needed a blood transfusion, and it would be separated into red blood cells bags and also plasma," she said.

The fact is that vets need blood to help injured and sick dogs that are brought in for treatment, and unwanted greyhounds provide a ready supply.

"They would be brought in by a trainer; normally we would get about three or four dogs and then they would be bled within about 48 hours of arriving," Ms Luxton-Bain said.

"So they would be put under anaesthetic and then bled and then euthanised while under anaesthetic."

Nurses and vets appalled by the practice

Queensland vet nurse Selena Cottrell-Dormer says a large percentage of greyhounds have a blood type referred to as universal, so most are able to receive it without having a transfusion reaction.

"Often they will be just absolutely bled to death and euthanised, put in a body bag and put in the freezer and taken away for incineration," she said.

"It's absolutely routine. No-one would bat an eyelid at that being the reality."

Ms Cottrell-Dormer described the draining process to 7.30:

"A non-recovery donation would have an intravenous catheter placed, then the dog would be anaesthetised and a tube placed down its throat so it's unconscious. "Then the femoral artery would be located ... it's a really large blood vessel in the inner thigh. A large needle would be inserted into that and about two litres of blood would be taken from the animal."

If the nurses are struggling to get blood out, they will give the dog adrenalin.

"At which point the animal would be euthanised by being given an overdose of an anaesthetic called lethabarb."

For Ms Cottrell-Dormer, draining a greyhound of up to two litres of blood was a task too hard to bear.

"I think it's the equivalent to essentially organ theft or rounding up the most vulnerable members of a community and exploiting them just because you can," she said.

"Just because you can doesn't mean you should, so most nurses are appalled by it and technicians are appalled by it, a lot of vets are appalled by it.

"I don't think there would be a vet nurse or vet technician out there who's worked in a larger referral hospital or larger veterinary clinic who hasn't had something to do with it, it's that standard."

The 7.30 program has heard from a number of other nurses too afraid for their jobs to speak out publicly about the practice.

Bleeding of dogs can help other patients

VSS animal hospital in Brisbane is one facility where greyhounds are bled and then euthanised for other animals that need transfusions.

Vet Dr Bruce Mackay says it has ethics approval from the Queensland Government and that up to 100 dogs are euthanised there each year.

"The charge for a bag of blood is $150. If we buy the same thing from the blood bank in Melbourne, by the time it gets here it's $400," he said.

"It's not what we as vets like doing, we're about saving animals, but sadly there are lots of greyhounds and other pet dogs that are not wanted.

"We look at this long and hard - I guess we feel it's ethical because these are dogs that would be euthanised and they can help other patients."

One animal hospital in Sydney has set up an alternative with the support of Greyhound Racing NSW, where adopted greyhounds make small donations like the human blood donor system.

Ms Cottrell-Dormer and Naveen Prakash have started a similar program in Brisbane.

They hope it is one small step towards ending the exploitation of these dogs.

"What we want to see is an elimination of greyhounds being killed for their blood," Ms Cottrell-Dormer said.