Mads Bertelsen, a veterinarian at the zoo, said that the animal had been afflicted by a skin disease for more than three weeks.
“We have done everything we could to save our rhinoceros, but it is also our job to assess when enough is enough,” he said in a press release.
“We have treated him extensively during this period, but the wounds in his mouth meant he had lost the desire to eat. He was now so weak that we didn't want to keep him alive any longer out of concern for his own wellbeing.”
The animal, which suffered from superficial nectolytic dermatitis, had lost as much as 400KG in weight in recent weeks.
The southern white rhinoceros was born in South Africa in about 1996 and came to Denmark four years later, first staying at Knuthenborg Safari Park on the island of Lolland, and then moving to Copenhagen Zoo in 2012.
He has already fathered three calves at the zoo, and is due to father two more early next year.
“In the midst of all the sadness, we can happily rejoice that this male rhino ended a baby-drought of more than 30 years in the rhino stable, first by becoming the father of a single rhino boy and then two more, who are currently running around the Savannah,” Bertelsen said.