A BBC investigation has uncovered huge gaps in how greyhound racing is regulated in Northern Ireland.
This has led to problems with over-breeding and retired dogs disappearing.
Greyhounds can live to 12 but most retire by five, leading animal welfare campaigners to suggest thousands of dogs are vanishing every year.
No single government department has responsibility for monitoring greyhound racing but the Department of Social Development regulates betting.
Racing greyhounds are well treated and when they retire the fortunate ones are kept by their owners. Some even run in veterans races.
Others are rehomed by charities and some will be put down humanely by vets.
But that still leaves a significant number of retiring dogs who are unaccounted for each year.
However, even before then, competition for successful dogs is so fierce that overbreeding is also a problem, according to animal welfare groups.
Campaigner Richard Hambleton from Carrickfergus said: "There's 25,000 dogs retired each year in racing, on average, across the British Isles.
"So to replace this they need more dogs but the problem is you breed dogs but you only put one forward out of the litter.
"That means the rest of the litter is put to sleep."
Currently no department at Stormont takes responsibility for monitoring greyhound racing but SDLP environment spokesman John Dallat wants the issue looked into.
"To be honest I am absolutely astonished that we do not have legislation that protects the industry against these people who quite clearly should not be in it," he told Radio Ulster.
"It may well be that there is a dark secret there that we need to start to looking at and taking responsibility for.
"In doing so I would be absolutely certain that we are helping the industry, not hindering it, because no industry needs the kind of people who put dogs into bags with a stone and drop them into the sea. That's disgusting."
Some of those who work in the industry dispute the number of dogs retiring from racing each year.
Barry Coleman, the welfare officer of the industry's governing body in the Republic, the Irish Greyhound Board said: "We would re-home greyhounds from Northern Ireland because greyhounds would also race in Dundalk and Lifford which are border tracks and many of the Northern Ireland people would come over.
"I don't know where you got that figure. It is the first time I have heard such a figure.
"I would not believe that there would be that many looking for homes at the end of their racing careers."
Julia Paul's investigation into the greyhound racing industry is on Radio Ulster on Sunday 18 March at 13:30 GMT.