I've just watched the last few fences of this race on youtube. It was indeed Many Clouds that was being whipped and I have to agree that according to the rules the use was excessive. The whip was used 5 times in the right hand between the last two fences then the jockey switched hands after the last I guess to stop the horse careering to the left and barging into the runner up Thistlecrack. It was difficult to say exactly how many times the horse was struck after the last fence as it was on the far side away from the camera but I counted at least another 5.

Here is a link to the rules regarding use of the whip. As I see it the rules state no more than 8 times on the flat and no more than 9 on the jumps before the stewards become involved, so this would in all probability be classed as a borderline case. 

http://www.thepja.co.uk/members-info/regulatory/useofwhip/