Difference Between a Filly and a Mare

Age is just a number but who knew it could give birth to two different words for the same species of animal. Due to age difference, the young female horse aged below 4 years is called a filly whereas the older ones are called a mare.

A Filly vs A Mare

The main difference between a filly and a mare is that filly is a general name given to a female horse that is below the age of 3 or 4 years whereas a mare is a female horse aged above 4 years. The filly is the name for a still-growing horse as their bodies go through a lot of physical change.

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The filly is the term used for a horse that is still in its growing period. However, they are sexually mature and can be used for reproduction. It is however not recommended to let a filly go through such a physically demanding process. A female yearling exhibits estrus during their growing period and hence it could cause some problems.

A mare a is fully grown female horse that can be used for various purposes such as horse racing and riding. The word mare is used to describe other female equine animals. The mare used for breeding is called a broodmare. The word is used to describe many female adult animals such as mules and zebras.

Comparison Table Between a Filly and a Mare

Parameters of ComparisonFillyMare
AgeThey are aged below 4 years.They are aged above 4 years
ReproductionThey should not be used for reproduction.They can be used for reproduction.
Physical developmentSome fillies undergo physical changes through the age period.They are fully matured and do not undergo any physical change.
Usage of the wordThis word is exclusively used for young female horses aged below 4 years.This term is used for various animals such as zebra, etc.
RidingThey cannot be used for riding purposes.They are used for riding.

What is a Filly?

The word comes from old Norse fylja used for young female horses. It is used for a female horse of age below 4 years according to some dictionaries. However, the age varies depending on the source from which you get the information. To be safe one could say if the horse is still in a physical development phase, then it should be categorized as a filly.

Most fillies go through some physical change and hence cannot be considered for breeding regardless of their sexual maturity which they achieve at the age of two. They can be spayed but due to it the complicated procedure it is less in practice.

The word filly is often confused with colt or foal. The words are used interchangeably for any baby horse but there is a distinction. A young male horse is called a colt whereas a young horse whose gender is unknown can be called a foal.

When it comes to riding, they are not considered but can participate in a race. The races are usually ‘in hand’ races which means that there is no rider. They however can be used in training but any horse below the age of 4 years is not considered for riding.

What is a Mare?

Mare is the term used for a fully grown-up female horse that can be used for riding and racing without restrictions. The term comes from old English mere which is female for the word mearh which means horse. Similarly, there are different words in German and other languages to which its origin can be traced.

Mares are used as dairy animals in various cultures found in central Asia. In Kyrgyzstan, the fermented milk of a mare is considered a national drink. Pregnant mares’ urine has some ingredients which are used to make drugs. Geldings are considered over mares and stallions however mares are also easier to handle as they are very calm.

The nomads called Bedouin preferred mares over stallions because they were quiet and was manageable. In many horse races, there is a separation based on sex but a few mares and fillies have won a competition against stallions.

It carries the baby horse in the womb for 11 months and gives birth to a single child. Twins are born but are rare. The wild mare nurses the foal for a year and the domestic ones do so for a period of 6 months. Mares goes through the phase of “heat” or “season” every 20 to 22 days but during winters they miss the cycle and the phase is called anestrus.  

Main Differences Between a Filly and a Mare

  1. Fillies are young horses below the age of 4 years whereas mares are fully grown female horses.
  2. Mares are considered for all kinds of races and can be used for riding whereas fillies cannot be considered for riding and all forms of horse racing.
  3. Mares are used for breeding whereas fillies cannot be used for breeding regardless of sexual maturity.
  4. Mares do not go through any growth but fillies go through significant growth during the period.
  5. The word mare can be used for other equine animals such as zebras, etc. whereas filly is exclusively used for the young female horse.


Filly and mare are words used to denote female horses but there is a difference in age. The word filly is used for the young ones under the age of 4 whereas the word mare is used for the female horses that are mature. Fillies and mares both can be used in races but fillies cannot be used for riding purposes and hence during a race they race alone without a rider.

The use of both types of horses is common for reproduction due to the sexual maturity that they achieve at a very young age of 2 years. However, fillies are not fit for the purpose as they go through physical changes during the period of 3 to 4 years.

Mares are celebrated in different cultures and in some nomadic cultures of central Asia their milk is used for various purposes. They are also preferred over male horses as they are calm and easy to handle.


  1. https://agris.fao.org/agris-search/search.do?recordID=US19930099224
  2. https://www.sciencedirect.com/science/article/pii/S0093691X08002690
  3. https://www.sciencedirect.com/science/article/pii/S0168159105000286
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