Horn trimming has become a well practised and documented phenomenon across South African private game reserves. Horn trimming is the process of cutting a rhinos horn, like we cut our hair. The first time a rhino has their horn trimmed, the majority of the external horn is removed, and then subsequent procedures trim the remaining horn as it continues to grow. Most reserves do this on an annual or biannual basis.
The most important thing to remember when discussing horn trimming is that rhino horn grows. Just like our hair, rhino horn continues to grow and so trimming does not leave rhinos without a horn permanently, and to keep the horn short will involve continuously trimming every year or so. This is a key argument in favour of legalising the rhino horn trade: you can sustainably harvest horn and continue to harvest horn from one rhino throughout its' entire life. Rhinos can live to be ~45 and horns can be trimmed every year, and so by horn trimming, you generate more product than if you left the horn alone.
The second most important fact to bare in mind is that horn trimming is incredibly expensive. To horn trim a rhino you need a helicopter + fuel, at least one vet, tranquilliser and other drugs, vehicles + fuel, and a whole team of people to move and monitor the rhino, including a scientist on site to record and take measurements (necessary for permits but is also provides important data into growth rates etc.). Vets alone incur fees for their time and their drugs. Most reserves don't own their own helicopter, and so have to hire one, pay for fuel, and pay for the pilot.
The main motivator for horn trimming rhinos is to act as a deterrent to poaching. Rhinos are poached specifically for their horns. Thus, a rhino with a trimmed horn is a much less valuable target than a rhino with a full horn. Is breaking onto a reserve, risking your life, and risking a life-sentence for rhino poaching worth it, for a horn maybe 1/4 of its original size? Ideally, we want the answer to be no to this question. The rhino poaching crisis in undeniably more complicated than that, but horn trimming does make rhinos a less desirable target.
If you're wondering why poachers kill rhinos when you can remove horns on a live animal, there are two primary reasons. Firstly, poachers often aren't qualified veterinarians with access to tranquillisers or dart guns (although corrupt vets have been implicated in rhino poaching in the past). Therefore, they shoot the animals and sometimes slash their spines to immobilise them. If they did not do this, the rhinos would either run away or charge at the poachers and potentially kill them. Secondly, poachers want to get as much horn as possible so they take the entire thing. The cut it out of the rhinos face to ensure they have every morsel of horn. This often happens while the rhino is still alive, and demonstrates the cruelty of this epidemic. This is why the rhino crisis sparks such emotion from people who work closely with these animals. It's human brutality in its ugliest form.
There has been no evidence to imply that horn trimming has a negative impact on rhinos. Darting animals, especially wild animals, is stressful for them, but this day of stress has not been shown to evoke any long-term suffering or negative effects on the animals. Furthermore, their social interactions have not been negatively affected by the process. Rhinos do not need their horns to survive. Horns are used in fighting, but reserves that do horn trimming do so on all their rhinos, and so the playing field is levelled and the rhinos fight anyway. Horn trimming has not been shown to negatively impact rhinos in the wild.
National parks in South Africa do not horn trim their rhinos. There are a couple reasons for this. Firstly, the cost is immense. Most private reserves, while owning 45% of all white rhinos between them, individually have smaller populations. National parks have many more rhinos, and so the costs are exponentially higher. Secondly, national parks rely on tourism for their income. It is generally believed that tourists want to see rhinos with big horns. The bigger the horn the better. Many think tourists would be disappointed to see rhinos with trimmed horns.
Personally, I think people would understand. If the guides and rangers could explain clearly why the rhinos have been de-horned, that it does not harm them or their social interactions, and use rhino sightings as an educational moment to enlighten tourists in the severity of the rhino crisis, then I think they would understand. It very much may be that your choice is a rhino with a trimmed horn, or no rhino at all. What would you choose?