Final answer:
The percentage of slow-twitch and fast-twitch muscle fibers in horses varies by breed and intended use, with thoroughbreds having more fast-twitch fibers for speed, and draft horses having more slow-twitch fibers for endurance.
Step-by-step explanation:
Horses have two types of muscle fibers: slow-twitch and fast-twitch, each comprising a distinct percentage of their muscle makeup.
The question about the percent of fibers in horses pertains to the composition of their muscles. In general, horses have a mix of slow-twitch (Type I) and fast-twitch (Type II) muscle fibers. The percentage of these fibers varies based on the breed and the type of activity the horse is bred for.
For instance, Thoroughbreds, which are racehorses, typically have a higher percentage of fast-twitch fibers, adapting them for speed and high-intensity activities. In contrast, draft horses, which are bred for endurance and strength, usually have a higher percentage of slow-twitch fibers. It's hard to say an exact percentage of fibers all horses have as it can range widely; specific figures would require a muscle biopsy and analysis of an individual horse or specific breed.