With only six northern white rhinos left in the world and three incapable of natural reproduction, the second largest land mammal species could soon be extinct.

In order to save the species from extinction, which is distinct from the southern white rhino that are found in a few thousands in southern Africa, in vitro fertilisation (IVF) seems to be the last possible hope, AP reports.

According to keepers of three northern white rhinos in Kenya, a male and two female rhinos will not be able to reproduce naturally.

One of the males at the conservancy died earlier this year. Veterinarians who examined the remaining three found that the male mammal's sperm count was very low and that two other female white rhinos either could not get pregnant, or could not carry out a pregnancy to term.

However, a southern white rhino could be a surrogate mother in case of an IVF experiment.

The Ol Pejeta Conservancy in Kenya, where the northern white rhinos have lived since December 2009, said that artificial reproductive techniques "could provide the last chance of survival for the world's most endangered mammal".

When transported from Nairobi to the conservancy, not many expected anything to come from the $100,000 effort and experts advocated that the money lent by a donor be spent on other conservation projects.

"They've been returned to Africa from a zoo, and they've thrived in that environment. In that way it's been a success," Richard Vigne, chief executive of the Ol Pejeta Conservancy said.

"The fact they haven't bred is clearly a massive disappointment, but there are new technologies being invented all the time to rescue technically extinct species."

The demand for rhino horn in Vietnam has resulted in more than 3,000 rhinos being killed by poachers in South Africa since 2010.

The white rhino is particularly vulnerable to poaching, because it is relatively not as aggressive, and move around in herds, according to WWF.

The northern white rhino could once be found in southern Chad, the Central African Republic, southwest of Sudan, northern Democratic Republic of the Congo (DRC), and northwestern Uganda. And in the 1960s, there were more than 2,000 remaining in the wild.

The two living white rhino subspecies are genetically distinct and only around 11,000 white rhinos survive in the wild.