When Do Horses Stop Growing?

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Horse’s growth is a hot topic in the Sporthorse industry and is an important concept for all horsemen to understand.  So, when does a horse stop growing? Horse growth determines when horses can begin their careers and when it is acceptable to ask them to perform in certain ways. 

Horses are done growing at different times for different categories of growth.  Their growth can be divided into height, weight, and bone. Horses finish growing up before they finish growing out, and they finish growing out before their bone development is completely done.

In this article, I will discuss all three of these growth categories to determine when a horse is done growing in each and overall.

When Does a Horse Stop Growing in Height?

A horse’s growth upward in height takes the least amount of time to complete.  If you think of foals or yearlings, they are often “all legs,” thin, and gangly. This is because they’ve grown in height more quickly than they have in weight.

Light, riding horses have grown to approximately 84% of their full height by the time they are six months old. They are 94% of their full-body height by the time they are twelve months/ one year old. And they are 97% of their full height by the time they are twenty-four months/ two years old.

Equinews illustrates this in an example of a thoroughbred, whose full height would be about 15.2 or 15.3 hands.  This horse would be 13.2 hands at six months, 15 hands at twelve months/ one year, and would be 15.2 hands at twenty-two months/approx. two years.  

Horses also grow out in length in about the same time as height.  Their spine lengthens as they grow taller.

When Does a Horse Stop Growing in Weight

A horse will grow out more slowly than they grow up.  Equestrians often refer to their horses as “filling out,” for many years while they are still young.  Young horses are often below the average weight until they have had time to fill out and gain muscle and fat they need to be a healthy, mature horse.

Horses will be between 46-50% of their total body weight at six months, about 65% and twelve months/one year, 90% at twenty-two months/approx two years. The remaining 10% will fill out progressively over the next 2-3 years, depending on the horse and its program.

Going back to the example from Equinews, this means that a Thoroughbred with a mature weight of 1100 lbs would be 506 lbs at six months, 715 lbs at twelve months/one year, and 990 lbs at twenty-two months/approx. two years.

When Does a Horse Stop Growing: Bones

Growth in a horse’s bones and joints is the most controversial topic in terms of horse growth.  Many trainers and owners feel strongly about what age it is appropriate to start breaking, riding, or jumping a horse.  This is largely in part to the growth process of a horse’s bones and joints.

There are studies that have shown that starting to work a horse while its bones are still developing can have negative consequences for a horse later in its career.  The industry most heavily attacked by these findings is the racing industry, where horses are raced at as young as two years old. It is also commonplace for many European breeders (and even some American breeders) to be jumping horses as early as three years old and moving up the heights very quickly.

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Everyone must make their own decisions regarding what is best for their horse and their horse’s training.  But, in order to make these decisions, one must be informed on what the growth process is in a horse’s bones and joints.

Growth Plates

Horses have growth plates on every bone in their body, besides their skull.  These growth plates can take up to six years to fuse.  This doesn’t necessarily mean that horses shouldn’t be broken or ridden until they are six years old;  it simply means that, until they are six, it is important to keep in mind that they are still developing.

Make sure you and your vet have a plan of action to best ensure your horse’s well-being.  Your young horse should be checked by the vet regularly to make sure your horse is growing and developing correctly.

Vets can also properly assess whether a specific horse is mature enough in its growth to perform certain tasks or jobs.  Every horse is different, and every rider and trainer will make different decisions. 

 Taking necessary precautions, regularly consulting with a vet, and staying informed on modern research are the best ways to ensure that a young horse is getting the best start possible.

Bone Minerals

Similar to growth plates, it has been proven that horses don’t hit their mature bone mineral content (BMC) until they are six-year-olds. The growth of BMC is even slower than a horse’s growth in height and weight.

Bone mineral content sounds like a fairly scientific term, but it simply means that a horse’s bones aren’t fully healthy and strong until they hit their mature BMC level at six years old.  Similar to growth plates, this doesn’t mean that horses shouldn’t be ridden until they are six, it simply means that due caution should be taken until all parts of their body have fully developed.

When Does a Horse Stop Growing in Height?

Conclusion

When a horse stops growing can be a difficult topic to analyze.  There are many aspects of a horse’s growth, but a horse should be completely done growing and developing by age six.  All horses are different, and some horses can physically handle more than others at younger ages.

I hope this article helped you better understand horse growth and when horses stop growing.  If so, please share this article, and share with us your experiences watching young horses grow and develop!

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