Hi Madhavshyam,
I'm not a groom expert but I do have some experience with rendering black fur. Unfortunately I could not get good results with Arnold and switched to Renderman for that. It has quite good docs, examples and presets.
From my exerience if you want to use Arnorld I would suggest making groom brighter so it can give more natural look.
The problem you are having is that dark areas of the groom look like a clean black color and in contrast with white highlights it looks unnatural. In real life there is no completely black color, it always has a tone or shade.
1 hack I did use with Arnold is adding transparency to the groom shader so more light can go through. It should help a bit but would not solve this problem completely.
Hope this helps !