Found on my new favourite blog, i'mrevolting.net, this is by Cai Guo Qiang, and is called Head On (2006).
From the artists' website:
With few wolves scattered in the front gallery, all ninety-nine wolves run, gallop, and jump toward the far end of the exhibition hall, where a wall stands. The bravery of the wolves is met head on by the unyielding wall. As the leading wolves go down, many more follow with force and determination. As those in the front fall and pile up, those behind take up their positions.