Mr Mallard visited the shelter with Dunedin South MP Clare Curran and Dunedin North MP David Clark.
During the visit, Mr Mallard asked SPCA Otago business development manager Kirsty Thomson if the shelter had any dogs from puppy mills.
A puppy mill breeds puppies for sale, typically on an intensive basis and in conditions regarded as inhumane.
Ms Thomson said the shelter had adopted out a corgi which had been at a string of ''puppy farms'' and the shelter once had an old shih tzu with bad hips from too much breeding.
As the shelter received no complaints about either dog, no action was taken, she said.
''We can only investigate if an official complaint is made and people don't tend to call us with enough information to act,'' Ms Thomson said.
Mr Mallard said people breeding puppies on farms to sell in pet shops and online was an issue around New Zealand.
A set of rules needed to be established on what was acceptable with dog breeding, he said.
''In quite bad conditions, with animals that are often inbred and not well looked after, because it's underground, you're never quite sure of the extent of it,'' he said.
Ms Thomson said it was the same with dog fighting. It could be happening but ''firm'' information was needed before the SPCA could take action.
Mr Mallard believed dogs were being stolen for use in fights, or as bait in dog fighting.
''It makes me sick to the stomach,'' he said.
The Animal Welfare Amendment Bill was before Parliament and he was concerned about the slow speed of its implementation to protect animals from cruelty.
''The minister [for Primary Industries Nathan Guy] has a discretion to defer implementation for up to 15 years and it seems we don't need to take that long.''
Giving farmers seven years to change their practices was reasonable, he said.
The Bill proposes amendments to the Animal Welfare Act 1999 to improve the enforceability, clarity, and transparency of the New Zealand animal welfare system.
