A young horse is commonly referred to as a foal, regardless of its gender. However, if the foal is male, it can also be called a colt, while a female foal is called a filly. While the foal is still nursing, it may be referred to as a suckling. Once it is weaned, it becomes a weanling.

After the horse reaches the age of one year, it is no longer considered a foal but becomes a yearling. Despite this transition, a young adult horse can still be called a colt or a filly. However, when a colt reaches a certain age, which may vary by breed, it is then referred to as a horse. Similarly, when a filly reaches that age, she is called a mare. A male horse that has been castrated is known as a gelding, regardless of its age.

A stallion is an intact male horse that has been used for breeding purposes, regardless of its age. On the other hand, any female horse that has been bred is referred to as a mare, regardless of her age. It’s important to note that these naming conventions may vary across different breeds, but the information provided holds true for Thoroughbreds.