Many greyhounds bred for racing are unsuitable for re-homing in retirement because they are systemically mistreated during their life, an inquiry into the industry has heard.

The New South Wales special commission of inquiry into the industry has started its second day of hearings with a focus on the life cycle of a greyhound.

Specialist greyhound vet Dr Karen Dawson told the inquiry today that 40 per cent of dogs bred for racing would never make the racetrack because of injury, unsuitability, failure to chase or other reasons.

Of those that did race, she said, many could not be re-homed in retirement or needed extensive rehabilitation because racing life had made them stressed, anxious or predatory.

This included a lack of socialisation with people and dogs on farms from an early age, lack of exposure to suburban life and stress from being isolated in kennels.

It led to more dogs being euthanased during their racing career because they were too stressed to race, or later being put down in retirement.

She showed the commission videos of retired greyhounds so traumatised they froze when led on a leash and lunged at other dogs.

"In my opinion a lot of dogs are unsuitable for re-homing," Dr Dawson said.

"It's the mental wellbeing of the dog that contributes to wastage more than the physical wellbeing.

"We cannot obliterate this behaviour in some of the dogs, we just can't."

Muzzles 'cause more stress'

She was also concerned by the widespread use of muzzles on stressed dogs, "which cause more stress and stress obviously compromises welfare and contributes to wastage".

She said wastage could only be reduced if the industry reviewed the entire life cycle of the dog.

Vet Leonie Finster said dogs running in circles in the same direction led to injuries from repetition.

She said muscle injuries often went unnoticed and there was a lack of pain relief in the sport.

"Greyhounds with muscle injuries don't show a lot of pain," she said.

The vet said the unqualified "muscle men" in the sport frequently used unproven and sometimes harmful treatments on dogs.

The inquiry heard the use of pin firing, banned in horse racing, was being used on greyhounds.

The inquiry was established after the ABC's Four Corners program uncovered widespread use of live baiting.