Rhino populations have been under heavy pressure from poaching. They are poached because some people believe that the horn of a rhino has medicinal qualities, and trade in rhino horn is very lucrative.
In the past years, there has been an effort to dehorn rhinos in several South African national parks and game reserves. A dehorned rhino has no value to poachers, so this is an effective way of protecting them – and the incidences of poaching have dropped significantly as an effect. For the rhino it does not seem to matter much. Fights over dominance can still happen, even without a horn, and may even be safer for the parties involved.
Still, it’s sad that we have to do this to protect a species!