What is a filly? This is just one of several words used to describe a horse's age and gender. The word is used to differentiate between a young male and female horse. All baby horses are called foals, but a filly or filly foal means that the foal is female.
Definition of Filly
A female horse under four years of age is called a filly. A female horse over the age of four years is called a mare. The plural of filly is fillies.
The broodmare had a newborn filly by her side.
The colt and filly played in the pasture.
Characteristics of Fillies
Many people feel that fillies are born with a bit more intelligence than colts. Some believe they’re quicker to gain their feet and start to nurse. Whether this is true or not is debatable.
Colts, however, may mature faster than fillies physically, especially if gelded at a young age. Some also believe that fillies are easier to sell than colts, largely because when buying a young horse that is un-gelded, the new owner must commit to the extra expense of castration. Fillies and mares can be spayed, but it is very unusual and a far more complicated procedure than gelding.
Incorrect Usages of Foal, Colt, and Filly
It is common for non-horse people to call all baby horses colts, but this is incorrect. A female baby is a filly and a male is a colt. Using the word "foal" is the correct way to refer to a young horse of unknown gender still with its mother. A young horse can be referred to as a filly foal or colt foal.
Once a filly is weaned, it may be called a weanling filly, and when it reaches the age of one, it may be called a yearling filly. After that age of two, it may be a two or three-year-old filly, but it wouldn’t be uncommon to hear a young female horse referred to as a young mare, even though this isn’t strictly correct.
Horse Racing and Riding Horses
In the horse racing world, the word filly has a slightly different meaning. In a race, a filly may be any female horse running under the age of five years old. The riding horse world rarely makes this distinction, partially because horses aren’t really ridden except in training before they are four years old. If a horse show class is specifically for fillies, the young horses will likely be shown "in hand" — that is, not being ridden.
Young donkey, pony, mule, zebra, onagers, and other equine relatives may be referred to as fillies as well.
Roots of the Word Filly
According to the Merriam-Webster dictionary, the word filly has been used in English since the 15th century. Its roots are in the Old Norse word "fylja" for female foal, that evolved to the Middle English word "filli" and is also similar to the Old English word for foal. The French word "fille" has similar roots.
In English, a slang way of saying girl may be to refer to her as a filly. In Australia, Champion Fillies day is celebrated with entertainment, food, fashion, and racing.