This article was translated using AI.
In a nutshell:
- Horses are only fully grown at 6-8 years (depending on the breed) – the last growth plates do not close until then
- Starting a horse too early puts strain on immature bones, cartilage, and growth plates, which can lead to permanent damage
- The spine, knee joints, and the long cannon bones of the legs are particularly critical
- Economic pressure leads to most horses being started at 2.5–3.5 years – far too early
- Long-term consequences include osteoarthritis, malalignments, back problems, and a shortened working life
When Do Which Growth Plates Close?
A horse's skeleton develops over years. Foals are born with a skeleton that still consists largely of cartilage. This cartilage gradually ossifies – a process called ossification. At certain points, the growth plates, the bone continues to grow in length. Only when these growth plates close – i.e., completely ossify – is the bone fully grown and capable of bearing weight.
The growth plates close in a specific sequence that is genetically determined. This sequence follows a principle: from the bottom up and from the outside in. This means the bones of the legs close earlier than those of the spine, and the joints lower down the leg earlier than those further up.
The growth plates on the pastern bones close at about 6-9 months. Those on the cannon bone (metacarpus and metatarsus) at about 9-12 months. The carpal joint (the "knee" of the front legs) closes between 2 and 2.5 years. The hock joint of the hind legs between 2.5 and 3 years.
Particularly important and often overlooked: The growth plates in the shoulder and pelvis area do not close until 3.5 to 4 years. The vertebral bodies of the thoracic spine are only fully ossified at 4 to 4.5 years. And the critical areas of the spine – especially the spinous processes of the vertebrae – do not close completely until 5.5 to 6 years.
This means: A three-year-old horse may already look quite large and strong, but its skeleton is not yet fully developed. The spine, which is supposed to carry the rider's weight, is not yet fully ossified. The spinous processes, where important muscles and ligaments attach, are still developing. The large joints of the shoulder and pelvis, through which forces are transmitted, are not yet mature.
What Happens When You Start a 3-Year-Old Horse?
When a horse is started while the growth plates are still open, it means putting weight on structures that are not yet designed for it. Cartilage is softer and less resilient than bone. Open growth plates are weak points in the skeleton. If these structures are loaded too early, various problems can arise.
Compressions can occur at the growth plates. The still-soft cartilage cells are compressed by weight and movement. In the best case, this only slows down growth at that point. In the worst case, the growth plate is permanently damaged, and the bone no longer grows evenly. Malalignments develop.
A classic example is "over at the knee" or similar conformation issues. If the growth plates in the carpal joint are loaded too heavily too early, growth can be stopped prematurely. The front legs then remain too straight or develop a forward malalignment. This malalignment, in turn, puts incorrect strain on other structures and leads to osteoarthritis in the long term.
The consequences of early loading on the spine are also serious. The vertebral bodies are not yet fully ossified, and the spinous processes are still soft. When a rider mounts, their weight rests on this still immature structure. The vertebrae can deform under this load. The spinous processes can grow asymmetrically or change position.
This can lay the foundation for later Kissing Spines. If the spinous processes are placed in an unfavorable position by early loading, they may be too close together from the start. A horse born with normal spacing may develop narrow spacing due to being started too early, leading to problems later on.
The musculature of a three-year-old horse is also not yet sufficiently developed. The thoracic sling muscles, which are supposed to lift the ribcage and carry the rider's weight, are still weak. If the young horse is nevertheless ridden, it cannot carry this weight correctly. It develops compensation patterns – exactly the wrong movement and muscle patterns that later lead to thoracic sling failure, front-heaviness, and other problems.
The resilience of tendons, ligaments, and joints is also still limited. The connective tissue is not yet fully mature. The joint cartilage is thinner and more sensitive. Overloading in this phase can lead to damage that only manifests years later as osteoarthritis or chronic tendon damage.
Long-term Consequences for the Spine, Joints, and Bones
The consequences of starting a horse too early often only appear years later. A four-year-old horse that was started at three may initially seem completely inconspicuous. But at six, eight, or ten years old, the problems begin.
The spine is particularly vulnerable. Horses started too early develop back problems more frequently. Kissing Spines occur in them at a younger age. The spine shows degenerative changes earlier. Osteoarthritis in the small facet joints develops long before the horse is old.
This is because the spine was under load during the critical growth phase. The vertebrae could not develop optimally. The spinous processes may be positioned unfavorably. The entire statics of the spine is impaired. And every year under the saddle worsens the situation because the foundation was not optimal from the start.
The large joints of the limbs also show earlier wear. The carpal joint, the hock, the shoulder, and hip joints – wherever the growth plates were loaded too early, there is a higher probability that osteoarthritis will develop. Joint cartilage damaged in youth does not regenerate. The damage remains and worsens over time.
Malalignments caused by uneven growth lead to uneven loading. A leg that is not perfectly straight puts asymmetrical strain on the joints. Over years, this leads to one-sided wear. The horse may develop lameness that is not caused by an acute injury but by chronic wear due to years of incorrect loading.
Tendons and ligaments overloaded in youth remain weaker and more vulnerable. There is evidence that connective tissue overstretched during the development phase never reaches its full strength. A horse worked too intensively too early may have a higher risk of tendon injuries throughout its life.
The psyche can also suffer. A young horse that is physically overwhelmed has negative experiences with riding. It learns that work is associated with pain and being overwhelmed. This can manifest as resistance, anxiety, or even aggression. Some behavioral problems in horses have their roots in being overwhelmed during training.
© Adobe Stock / kwadrat70
Why Are Horses Still Started So Early?
If the disadvantages of early starting are so clear – why is it still practiced? The answer lies in economic considerations and traditional ideas that are not based on biomechanical knowledge.
Economically speaking, a horse costs money: feed, stable, veterinary care, farriery. A horse that cannot yet be ridden does not bring in money. Breeders and rearers want to be able to sell their horses as early as possible. As a rule, ridden horses are bought. So horses are started early to make them marketable sooner.
Economic pressure also plays a role in sports. A sport horse should achieve success as early as possible. A dressage horse should start in novice classes at four, in elementary classes at five. A show jumper should jump its first courses at four or five. This is only possible if the horse is worked intensively at three.
The short useful life in high-performance sport reinforces this problem. If a horse is only used intensively in sport until eight or ten years old anyway, long-term damage that only appears at twelve or fifteen plays no role from an economic perspective. The horse has already fulfilled its economic function by then.
Traditional ideas also play a role. "We've always done it this way" is a common argument. The realization that horses are only fully grown at five or six is relatively new. Previous generations did not know this and started their horses at three. This tradition continues without being questioned.
Ignorance also contributes. Many horse owners simply do not know how long it takes for a horse to grow up. They see that their three-year-old horse looks big and strong and think it is ready for the saddle. That important developments are still taking place internally, in the skeleton, is not visible from the outside.
Last but not least, there are also psychological factors. The anticipation of finally being able to ride is great. The patience to wait another year or two is difficult. "Just a little bit of work", "just light work", "just walk and trot" – this is how early riding attempts are justified. But even light work is a strain on an immature skeleton.
Ideal Timing for Training Under Saddle
If you prioritize the horse's health over economic considerations, the answer is clear: the ideal time to start training under saddle is between the ages of six and eight.
At six years old, most important growth plates are closed. The vertebral bodies are largely ossified, and the large joints are mature. The skeleton is capable of bearing weight. At the same time, the horse is still young enough to learn well and not be stuck in problematic behavioral patterns.
At seven years old, even the last areas – especially the spinous processes of the vertebrae – are completely closed. The horse is physically fully mature and can also be worked more intensively without concern.
This does not mean that you should do nothing with the horse until it is six. On the contrary: the years before starting are important for preparation. Groundwork, leading training, getting used to different situations, desensitization – all of this can and should be done from an early age. Lunging work without rider weight is also possible and sensible from about three years old to develop muscles and teach the horse basic commands.
The crucial thing is that no weight is put on the back as long as the growth plates are still open. Putting a saddle on to get the horse used to it is not a problem. Briefly mounting while standing as preparation is also fine. But regular riding, even if it is only at a walk, strains the immature structures.
Some experts even recommend waiting until the seventh or eighth year, especially for horses intended for demanding sporting use. One more year of physical maturation can make the difference between a horse that remains healthy into old age and a horse that already has massive problems at ten.
Exceptions and Individual Differences
Of course, there are individual differences. Some horses are fully grown earlier, others later. Large, heavy Warmbloods often take longer than smaller, lighter horses. Late-maturing breeds like Icelandics or Fjord horses need more time than early-maturing Thoroughbreds.
Gender also plays a role. Stallions tend to take longer than mares because they develop more muscle mass and their skeleton is more massive. A stallion should be started closer to seven than six.
One cannot see exactly from the outside of an individual horse whether all growth plates are closed. X-rays can show this, but they are elaborate and expensive. As a practical rule of thumb: the later you start backing, the more certain you are that the horse is physically ready.
Another important factor is muscle development. Even if the growth plates are closed, it does not automatically mean that the horse can carry a rider. The thoracic sling muscles must be sufficiently developed. This is achieved through groundwork, lunging, and free movement – not through early riding.
When you ride a young horse for the first time, you should proceed very carefully. Short units of 10-15 minutes, initially only at a walk, only on good ground, with a light rider. The intensity and duration should be increased very slowly. In the first year under saddle, training should be playful and varied, with lots of stretching and no demanding lessons.
Human Responsibility
The decision of when a horse is started lies solely with the human. The horse cannot say whether it is ready or whether it is in pain. It can only signal through its behavior when something is wrong – and these signals are often overlooked or misinterpreted.
Responsibility lies with the breeder, the rearer, the trainer, the buyer. Everyone who deals with young horses should be aware of the importance of the growth plates. Everyone should understand that every year you give a horse more time to mature physically is an investment in its health and longevity.
In an ideal world, all horses would only be started at six or seven. They would then have a fully mature skeleton, well-developed muscles, and the best conditions for a long, healthy life as a riding horse. In reality, this will not be possible everywhere. But everyone can contribute within their means to ensure that horses are not burdened unnecessarily early.
And everyone who buys a young horse or sends it for training can ask: How old is the horse really? Was it started gently? Did it have enough time to mature physically? Demand influences supply. If more people are willing to pay for a six- or seven-year-old, well-prepared horse, practice will change.
Starting horses too early is an avoidable problem. It requires only one thing: patience. Patience to give a young horse the time it needs. This patience pays off in the form of a healthy, long-lived partner who enjoys working into old age.
