Veterinary students have expressed concern over the hundreds of healthy greyhounds ending up as cadavers in their classes because they were no longer competitive.

One university student has written to the NSW parliamentary inquiry into the $144 million greyhound racing industry, which will resume hearings on Wednesday in Newcastle.

''As a vet student I believe it is my obligation to inform you of the realities of the current state of greyhound racing,'' the student wrote.

''It is easy to forget the reality of the greyhound who did not compete this racing season … for me, walking into an anatomy lesson and seeing hundreds of donated cadavers (you'd be hard-pressed to find a non-greyhound) literally piling up is a very real and constant reminder. To the university's credit, all cadavers are legally obtained and nothing is done wrong. But the fact there is a surplus of 'donated' dogs is very sad.''

Another student said: ''At uni, the breed of dog we investigate are greyhounds - because there are hundreds of them being dumped at the RSPCA shelters.''

Greens MP John Kaye, the deputy chairman of the committee running the inquiry, has already heard evidence that many healthy dogs are being killed because they were not fast enough or did not chase. The numbers remain unknown because they just disappear without trace every year.

A veterinary nurse has also made a submission saying: ''At my hospital alone we euthanise over 100 greyhounds a year, usually between the age of 2-4 because they suffer from either slow runners or non-chasers disease. This is what they call it.''

Dr Kaye said vet students were finding themselves at the front line of the unwanted greyhound crisis.

''Their trauma viewing the sheer number of greyhounds donated for use in anatomy lessons is a solid measure of the depth of the problem and the urgency of regulating the industry to reduce the number of dogs that are thrown away,'' he said.

Dr Kaye said responsible vets and universities who ensure greyhounds receive a humane death are not to blame for the number of dogs being killed.

At some veterinary schools, cadavers are obtained by the euthanasia of healthy but unwanted animals, such as pound dogs and ex-racing greyhounds, or purpose-bred dogs, according to a paper by Catherine Tiplady and other researchers from the University of Queensland.

Another paper, by Siaw-Yean Woon from the University of Sydney, stated the main source of cadavers were ex-racing greyhounds.

But veterinary schools declined to speak about the number of greyhound cadavers they receive.

Dr Kaye said vets and nurses were put in a terrible position when they had to destroy a greyhound. They must violate their professional instincts by putting down a healthy dog or allow them to go to an ''uncertain and potentially terrifying fate'' at the hands of someone else.

A veterinary nurse has told the inquiry she has ''nightmares'' about it.

''I've witnessed the death of too many greyhounds. It's heartbreaking watching them take their last breath and see the light go out in their eyes all because of something that is far bigger than you or me and there is nothing I can do about it.''