In a steamy Sumatran jungle the senior veterinarian for Taronga Western Plains Zoo grabbed drugs that could revive his hefty and unconscious patient.

But Andalas, the Sumatran bull rhino with the hope of the world conservation community riding on his big shoulders, rallied without intervention.

After a "short period" he started breathing again, as did Dr Bryant and the crowd who gathered to watch a procedure that has the potential to stave off the looming extinction of the Sumatran rhino.

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Dr Bryant looks at photographs of his excursion to the Sumatran Rhino Sanctuary for four days this month and admits he appears "serious and sweaty".

With less than 100 Sumatran rhinos remaining on the planet, he was nothing but nervous about knocking out and keeping alive the "only competent breeding bull in captivity".

Anaesthetising of the bull allowed scientists from Cincinnati Zoo to collect semen in a desperate bid to preserve an ancient creature.

An artificial insemination program has been launched at the sanctuary where the veterinarian from Dubbo has become a familiar face.

The full anaesthetising of a Sumatran rhino and the bid to breed more of them by artificial insemination are brave new steps.

But Dr Bryant is not convinced the Sumatran rhino's march to extinction can be halted.

"You've got less than 100 animals occurring in seven or eight areas in two countries," Dr Bryant said from his Dubbo workplace.

"They don't even meet for breeding. There's not enough to sustain natural... courting and mating when the time is right. That's what we're confronting now.

"Conservation statisticians will tell you that below a certain threshold of individuals there's just not enough animals for a population to bounce back anymore... and 100 is approaching that kind of threshold level."

But no one in the worldwide conservation community is giving up, least of all Dr Bryant.

"While ever there is a male and a female Sumatran rhino you're going to be desperately trying to perpetuate the species," he said.

"It would be just unbearable if they went."

There was a time when Sumatran rhinos existed potentially in their tens of thousands and roamed all the way up to China.

In the past decade surveys have counted between 250 and 300.

Dr Bryant said Sumatran rhino numbers in the jungle continued to fall, but not because of poaching.

The establishment of rhino protection units had proven "very effective".

"Poaching in South-East Asia is far less of an issue at the moment for the Asian species of rhinos than it is in Africa," the veterinarian said.

"In Asia habitat loss is a real issue and that's largely attributable to the incredible expansion in farming of palm trees for palm oil."

The Sumatran Rhino Sanctuary was established in the late 1990s in response to the crisis.

Dr Bryant describes it as a semi-captive facility where animals are managed in huge spaces in their natural environment.

In 2012 the sanctuary celebrated its "first naturally-conceived" calf with Dr Bryant on hand to deal with complications should they arise.

He reports that the calf is among a handful known to have been born in captivity.

The conception was not as smooth as the birth.

"They spent the last eight or nine years working towards breeding an animal naturally," Dr Bryant said.

"Even that's challenging with this species."

The veterinarian said in the past when Sumatran rhinos were widely kept in zoos, they became "notorious for killing each other during breeding introductions".

"Their courtship is very aggressive, particularly if they are not absolutely ready to mate," he said.

Sanctuary staff acquired and used reproductive ultrasound skills in helping bring new hope to the Sumatran rhino world.

Dr Bryant's trip to Sumatra this month is not his first nor probably his last.

He has supported the sanctuary for the past six years on happy and sad occasions that include the death of an old rhino with kidney disease.

"We really invested a lot of time and energy in alleviating his symptoms and in particular managing him through the final stages of his illness as he approached death," Dr Bryant said.

Taronga Conservation Society Australia was approached for help because of its acknowledged expertise in rhino husbandry and management, particularly at Taronga Western Plains Zoo in Dubbo.

"We've got one of the most significant collections of rhinoceros in a zoo in the world and we've had a highly successful and acknowledged breeding program," Dr Bryant said.

"Conservation, we're all in it together, and there's no doubt about it being a significant part of Taronga's agenda and brief."

In a month Dr Bryant hopes to hear that a female rhino at the Sumatran Rhino Sanctuary is pregnant because of the procedure performed on Andalas.

It was the second time he had fully anaesthetised the bull rhino that weighs 760 kilograms and is about 2.2 metres long.

"It's a very intimidating prospect because obviously he's absolutely irreplaceable," Dr Bryant said.

"I was very nervous because the world zoo vet community has very little experience of anaesthetising these animals.

"I don't have the benefit of a swathe of collective experience and data applicable to his anaesthesia so I'm kind of evolving an approach as I go based on my experience with white rhino, black rhino and greater white-horned rhino anaesthesia here and elsewhere."

Making sure Andalas made it through the surgery wasn't the only pressing concern for Dr Bryant in a pen in the jungle on May 16.

"I am monitoring his status under anaesthesia, incredibly carefully, looking for any evidence that his anaesthetic depth is becoming too great... which left unchecked progresses to death," the veterinarian said.

"I'm also monitoring him for any signs his anaesthetic level is too light, in which case he will jump up and start killing people."

For the record Andalas woke up, hopped up and left the pen without a stumble.

Dr Bryant watched him for another day-and-a-half before giving the all-clear.