Have a read of this, this is how the government spends out tax dollars. 

Another 54 have been vaccinated by dart shot by a government shooter, which is how it must be done if the method is to be used in the wild.

But the government has struggled to find a way to vaccinate and mark the kangaroos at the same time. In February last year, the senior ecologist in charge of fertility program, Claire Wimpenny, said the dart was too heavy when vaccine and dye were in one shot. With the contraceptive in one chamber and the marker dye in another, the vaccine had to be shot either at close range or at speed, and when shot at speed it hit with too much force.

So in mid 2016, 54 kangaroos were vaccinated by two shooters working together - synchronising their shots so one delivered the vaccine and the other the dye before the kangaroo was spooked and moved. But because the dart containing the vaccine and the dart containing the dye are different weights, they travel at different speeds, and Ms Wimpenny said the shooters had to work on "getting in sync".

"That did take a little bit of practice but by the end of it we had a pretty good system," she said. "We managed to have quite a high success rate."

Both darts had hit a single kangaroo in about 75 per cent of the 54 cases.

At one site, both shooters had hit the kangaroo in 80 per cent of cases.

Senior government ecologist Claire Wimpenny in Weston Park, where the government has been conducting a kangaroo fertility trial. Photo: Rohan Thomson

With "further refinement and practice", that could be improved, making the two-dart method feasible for treating wild populations.

But Ms Wimpenny said delivering the vaccine and dye in separate darts was not ideal and the project still hoped to find a way of marking and vaccinating with one shot.

"Hopefully between now and next deployment we would have a single system," she said.

The next round of vaccination would be done mid-year, but meantime the budget for the fertility trial is coming to an end.

The trial was announced by then minister Shane Rattenbury in early 2014 as a two-year project to vaccinate 500 kangaroos. A year later, in early 2015, then minister Simon Corbell said field trials were about to begin on about 200 kangaroos, with a two-year budget of $530,000.

Ms Wimpenny said in mid-2016, funding had been extended for a year, for a total over three years of $612,000 "plus some in-kind support". It is unclear what happens after June this year.

In 2015, Mr Corbell said it was already well known that the contraceptive, GonaCon, was effective when administered by hand, rendering kangaroos infertile for up to six years.

"Everyone understands GonaCon works when you inject it by hand, but the problem with that is you've got to subdue the kangaroo first," he said. "No one else has demonstrated the capacity to deliver GonaCon by dart."

Nevertheless, 81 of the trial kangaroos have been hand-injected. Ms Wimpenny said results from the first breeding year had shown it to be highly effective.

Twenty-one of the hand-injected kangaroos hadn't reached breeding age when they were vaccinated, so the results from that cohort were not in.

Of the remaining 60 hand-injected kangaroos, 52 animals did not breed in the first year after vaccination. Of the eight which did, most had very large pouch young when treated so were ready to breed again very soon and might have given birth before the vaccine had become fully effective, she said.

All but one of the 10 placebo-injected animals had bred in the first year.

The effectiveness of the first year of dart-delivered vaccine would not be known until later in the year when any young were born.

Ms Wimpenny said there was "still a long way to go" before kangaroos could be vaccinated in the wild.

GonaCon was yet to be registered for use in Canberra, other than for research. To get it registered, the dart-injected animals would need to be followed for four to five years.

"If it works as well as hand injected, definitely we're on to a really good product, but it's too early to say," she said. "I believe that the delivery system is there and I think that we can get that side of it done, but whether or not the efficacy is there, I'm not willing to comment yet."

The trial is a collaboration with the CSIRO.