Because of his age, Sudan is too frail to risk being left alone with the females in his enclosure, who themselves have medical problems that mean it is unlikely they could give birth naturally.
So in an attempt to save the species an international team of zoologists hopes to create the world's first IVF baby rhino, which could be born at Longleat Safari Park in Wiltshire, England.
However, the procedure poses many greater challenges than in human IVF, particularly because the animals are so large, weighing 1.5 tons.
A team of experts have visited Longleat and harvested nine eggs from the zoo's three female southern white rhinos, Morashi, Razima and Ebun.
The eggs have been frozen and transported to a laboratory in Italy to be fertilised with sperm extracted from Sudan and other male northern white rhinos that have since died. If successful, the resulting IVF embryos will be implanted into a selected group of female southern white rhinos - possibly at Longleat - later this year.
Angalifu, one of the extremely rare northern white rhino, died in 2014.
Dr Robert Hermes, an expert in rhino reproduction, said: "On any other animal this treatment would be pretty straightforward but with the rhino being so large and long it needs special equipment that makes the whole process very, very difficult."
Experts hope to use this method to eventually harvest eggs from the two living female northern white rhinos to produce a "pure northern white rhino" embryo to preserve the endangered species.
But they do not want to risk harvesting their eggs - a process which would involve anaesthetising the rhino - until they have perfected the method using southern white rhinos.
If this is not possible, scientists could carry on mixing the eggs they have collected from southern white rhinos with sperm from northern white rhinos to create a hybrid species.
Jon Merrington, head of safari at Longleat, said that without human interference driving them to the point of extinction, the two populations would probably have mixed anyway.
"What we're doing here probably isn't too far removed from what could have happened in the wild," he said. "This IVF and embryo transfer programme truly is the last best hope to save them from extinction."
Although closely related, southern and northern white rhinos are two distinct sub-species which are thought to have begun diverging around a million years ago.
Although closely related, northern and southern white rhinos (pictured) are two distinct sub-species.
There were more than 2000 northern white rhinos in existence in the 1960s but they have been wiped out by poachers for their horns, which can sell for tens of thousands of dollars.
Southern white rhino (Ceratotherium simum simum) populations are concentrated in the south of Africa where their wild numbers are estimated at around 20,000.
Meanwhile, although Sudan is not allowed to mix with the females, he has a horse to keep him company called Njema.
Sarah Vigne from the Ol Pejeta Conservancy in Kenya, where the last three rhinos live, said: "The management feel that Njema provides Sudan with good company. Njema is very placid, friendly and inquisitive."
She said that while seeing different species form a bond was quite common, she was not aware of any previously documented friendships between horses and rhinos.
