What type of training is used to develop a horse’s speed?

The correct choice focuses specifically on "speed work," which refers to a targeted training regimen designed to enhance a horse's maximum velocity. This type of training typically includes short, high-intensity sprints, allowing the horse to build muscle memory for fast racing. Speed work helps improve the horse's acceleration and overall performance on the racetrack, emphasizing quick bursts of speed over longer distances.

In contrast, endurance training concentrates on building stamina and the horse's ability to maintain a steady pace over long distances, which is not aimed directly at increasing speed. Strength training involves building muscle power but does not specifically address the rapid acceleration or quick speed that is critical in races. Balance training, while important for a horse's overall athleticism and coordination, does not focus on speed development either and is more aligned with maintaining stability and control during movement. Therefore, speed work is the most appropriate method for developing a horse's speed, making it the correct answer.