Just a genetic quirk ZZ, and apparently it doesn't affect the animal.
It could well be a genetic abberation, there's a name for it which I can't remember right now. I suspect it is not the case with this specific individual though.
When antelope have this genetic deformity the horn typically just droops at a funny angle. This horn seems to be the shape of a normal healthy horn, just pointing in the wrong direction. I would think that it is partially broken off, due to a bout of dominance with another male perhaps?
And it certainly does affect the animal. It might not affect his grazing or anything (because Impala don't use their horns to graze:wink:) but if you think about it, why do they have horns in the first place?
1. They use their horns for defense. This is not particularly significant in the case of Impala because they hardly ever use their horns in defense. A Gemsbok with a broken horn would suffer more significantly from a broken horn than an Impala as regards the usage as defensive weapon. It may single him out in a herd as being weaker than the others though, making him a target for predators.
2. They use their horns to assert their dominance in the herd. This individual stands no chance of becoming the alpha male and will always have a fairly low status in the herd. Consequently he will have a lesser chance to reproduce and carry his genes into the next generation of Impala.
On the short term, this might not seem like much because if an Impala has grass to eat, it's happy right? Well, not quite. Impala eat grass so that they can reproduce. The same holds true for all organisms. Their primary goal is to survive and reproduce. This poor chap may survive but will have diminished chances of reproduction.
And he will get very litte "jiggy-jiggy" in his life, shame...