Sark

A sark (or Sargh) was a type of animal lifeform, presumably native to Qo'noS, that were used as beasts of burden and as riding animals on many worlds colonized by the Klingon Empire. 

They bore some similarity to Terran horses, but with two straight, meter-long horns and flail-like tails.

Sarks may attack humanoids if provoked or very hungry. Furthermore, they were known to travel in herds, and may at times stampede. 

Klingons would sometimes play games on sarkback, including one that involved copying mimicking the motions of another rider.