What is the origin of the idiom "healthy as a horse" and when to use it?

The idiom "healthy as a horse" likely originated in the 19th century. Horses, known for their strength, vitality, and endurance, were used as symbols of good health, which led to the development of this expression. It is used to describe excellent physical health or condition, often in a positive and emphatic manner. It is commonly used in everyday speech and writing to emphasize good health.