Labor senator Glenn Sterle picked up the trail after Australia's inspector-general of biosecurity found dog numbers had almost halved between 2012 and 2017.

Agriculture Department deputy secretary Peta Lane has confirmed there were 35 sniffer dogs in service, with another four in training.

She said the canine sleuths were working more efficiently than in previous years.

"They would have worked a mail centre shift in the morning and then be essentially redundant for part of the afternoon," she told a Senate estimates hearing in Canberra on Tuesday.

"Now we're actually using those dogs in the mail centre in the morning and moving them to the airport in the afternoon."

Senator Sterle said: "You've doubled their shift?"

Ms Lane insisted the welfare of dogs was a high priority, noting they were one important tool in a suite of biosecurity protections.

"We're not working them more than we need to, but they're serving more purposes," she said.

Senator Sterle, a former Transport Workers Union official, wondered if he might have a future career in organising sniffer dogs.

With African swine fever decimating pig herds across Europe and Asia, Australian dogs are a crucial weapon in the fight against the devastating diseases.

Suki was redirected from Norfolk Island, which is now without a dog, to work in Darwin patrolling flights from East Timor, where the disease has been detected.

Officials said money from the government's delayed biosecurity levy could be used to train more dogs.

But Agriculture secretary Daryl Quinlivan denied the delay had affected the overall biosecurity budget.

He confirmed a further deferral of its implementation, which had been mooted to start on July 1, would be announced in the mid-year budget update.

Australian Associated Press