Mr Mallard's visit came after a Labour Party petition calling for a ban on animal testing of synthetic highs was signed by more than 40,000 people.
In Wanganui Mr Mallard visited the fire service and Sport Wanganui, and helped deputy mayor Hamish McDouall prepare for his election campaign for the Whanganui seat held by Chester Borrows.
Mr Mallard, who owns two Australian shepherds - 5-year-old Jeeves and 12-week-old Violet - was "feeling really pleased" after Prime Minister John Key announced the Government would be banning animal testing on legal highs.
"Public opinion is quite clear on it," said Mr Mallard.
"I'm not an extremist in this area - I know the value of animals in research for human therapeutic purposes where you're saving lives.
"In this case, where it's just for recreational drugs, the idea of killing beagles or other dogs - or even rats - to make bigger profits for the drug manufacturers and dealers is just wrong."
Parliament will pass legislation this week to pull all legal highs off shelves until they can be proven safe by testing, but Mr Key ruled out testing on any animals aside from rats.
"The advice I've had from the Health Department over the weekend is that they don't believe that that's safe," he told Newstalk ZB.
"They say it has to be on two species, not one, so what I've said is, 'Okay, well if that's what you believe, then it's all out'."
It was a victorious moment for Labour, whose petition to ban animal testing gathered 40,000 signatures in 48 hours.
"I'll let you in on a secret - we thought the goal would be 10,000," Mr Mallard said.
The petition is due to be presented in Parliament on Thursday when they aim to have 45,000 signatures.
Mr Mallard said the petition had helped push forward the announcement and bring the issue into the public eye.
"The issue was always there. We weren't quite sure which way John Key was going to jump - last we heard he was for rats but not rabbits."
