Two rhinos were darted and dehorned at Fairy Glen Private Game Reserve in Worcester, near Cape Town, according to a news report on Monday.
Both survived the attack by a gang of poachers, but one of them had to have an abortion due to the strain the attack put on her body, the Star newspaper reported.
Game farm owner Pieter de Jager said that his staff found the rhino bleeding and unconscious.
The rhinos had been darted with an overdose of M99, a morphine drug, and their horns were hacked off with pangas.
A Worcester hospital was able to provide an antidote for the drug and vet Roland Bellstedt was attending to the mutilated rhino.
The darts were sent for forensic analysis in the hope of apprehending the poachers. De Jager said it was difficult to defend the animals.
"Aside from sleeping next to my animals at night, guarding them in the bush, there is nothing I can do.
"The poachers are well-trained armed criminals," he said.
Over 400 rhino have been poached in 2011.