Growth Plates: Everything You Need to Know
- Horse Education Online
- 2 hours ago
- 12 min read
Structure, Function, and Development
Growth plates are one of the most important parts of the growing horse's skeleton. They are the reason a foal’s legs lengthen, the reason young horses change shape as they mature, and one of the reasons training decisions must be matched to age, development, and individual condition.
Growth plates are also called physes or epiphyseal plates. They are specialized layers of cartilage located near the ends of long bones. In young horses, these cartilage regions are active sites of bone growth. As the horse matures, the cartilage gradually turns into bone through a process called ossification. Once a growth plate has fully ossified, it is considered closed, and that part of the bone can no longer lengthen.
For horse owners, growth plates matter because they are closely connected to skeletal development, soundness, injury risk, and training readiness. A young horse may look tall and strong from the outside, but parts of the skeleton may still be developing on the inside. Understanding how growth plates work helps owners make more informed decisions about nutrition, exercise, turnout, conditioning, and when to increase athletic workload.
This article explains what growth plates are, how they help bones lengthen, when they close, and why they are so important in the management of young horses. Our article Is Your Young Horse Ready for Work? is an introduction to this topic.
Recommended Study Tools and Aids:
What Is a Growth Plate?
A growth plate is a cartilaginous region located between two major areas of a long bone: the epiphysis and the metaphysis.
The epiphysis is the end portion of a long bone. It is usually found near a joint. The metaphysis is the region between the end of the bone and the shaft. The long central shaft of the bone is called the diaphysis.
In a young horse, the growth plate sits between the epiphysis and metaphysis. It is not simply a soft gap. It is a highly organized biological structure filled with cartilage cells, blood supply connections, and extracellular matrix. Its job is to allow the bone to grow in length.
Unlike mature bone, cartilage is more flexible and less mineralized. This makes growth possible, but it also means open growth plates can be more vulnerable to injury or abnormal stress than fully mature bone.
Did You Know? Growth plates do not all close at the same time. In general, growth plates lower in the limb close earlier, while some areas of the spine and axial skeleton may continue maturing much later. This is why a young horse can appear nearly full-sized while still not being skeletally mature in every region.
How Growth Plates Make Bones Longer
Long bones grow through a process called endochondral ossification. This means that cartilage is gradually replaced by bone.
The growth plate works like a carefully organized production line. Cartilage cells, called chondrocytes, go through several stages. These stages allow the bone to lengthen while maintaining strength and shape.
The main zones of the growth plate include:
Resting Zone
The resting zone contains relatively quiet chondrocytes and extracellular matrix. These cells are not rapidly dividing. Instead, this zone acts as a reserve area. It helps maintain the growth plate and provides cells that will later participate in growth.
For beginners, it may help to think of this zone as the “starting area” of the growth plate.
Proliferative Zone
In the proliferative zone, chondrocytes begin dividing. They line up in organized columns. As these cells multiply, they help push the ends of the bone farther apart. This is one of the major steps that allows the bone to lengthen.
The organization of these columns is important. Healthy bone growth depends on the growth plate maintaining a structured pattern.
Hypertrophic Zone
In the hypertrophic zone, chondrocytes enlarge. The word hypertrophic means "enlarged". These cells also help prepare the surrounding cartilage matrix for mineralization.
At this stage, the cartilage is getting ready to be replaced by bone. The cells are no longer simply dividing. They are changing in size and function to support the next phase of growth.
Calcification and Ossification
After the cartilage matrix mineralizes, blood vessels enter the area. These blood vessels bring bone-forming cells called osteoblasts. Osteoblasts replace the cartilage with bone tissue.
This is the final step in the growth process. Cartilage is gradually converted into bone, while the growth plate continues producing new cartilage as long as it remains open.
Once the growth plate closes, this process stops in that region. The bone can still remodel and strengthen, but it can no longer grow longer from that physis.
Endochondral Ossification: The Growth Mechanism
Endochondral ossification is the biological process that allows the skeleton to form from cartilage models. It begins before birth and continues as the foal grows.
What does Endochondral mean?
Endochondral breaks down into two main parts:
endo- = within, inside
chondral = cartilage
So endochondral literally means “within cartilage” or “inside cartilage.”
In the phrase endochondral ossification:
endochondral = within cartilage
ossification = the formation of bone
In simple terms, the process works like this:
The developing bone begins as a cartilage template.
Cartilage cells divide and enlarge in a structured sequence.
The cartilage matrix begins to mineralize.
Blood vessels invade the area.
Bone-forming cells replace cartilage with bone.
Bone lengthening continues as long as the growth plate remains open.
This process is regulated by genetics, hormones, nutrition, blood supply, and mechanical loading. It is not random. A healthy growth plate depends on a balanced internal environment and appropriate external forces.
When this process is disrupted, the result may be abnormal bone shape, inflammation of the growth plate, uneven growth, or developmental orthopedic disease.
Growth Plate Closure and Skeletal Maturity
Growth plate closure happens when the cartilage of the physis is fully replaced by bone. Once closed, the growth plate is no longer visible as an active cartilage region, and the bone has stopped lengthening at that site.
In horses, growth plates close in a predictable general pattern, but exact timing can vary. Breed, sex, nutrition, genetics, growth rate, management, and individual development may all play a role.
Approximate examples often cited in young horses include:
Region | Approximate Closure Timing |
Coffin bone | Before birth |
Some phalangeal growth plates | Within the first several months of life |
Distal metacarpal and metatarsal region | Around 9 months |
Distal tibia | Around 18 months |
Distal radius | Around 2 to 2 1/2 years |
Axial skeleton and vertebral regions | May continue maturing later, sometimes into 4 to 6 years |
These ages should be treated as general guides, not absolute rules. The most important concept is that different parts of the skeleton mature at different times.
A yearling is not the same as a mature riding horse. A two-year-old may be close to adult height, but some growth plates and skeletal structures may still be maturing. Even after obvious height growth slows, the skeleton continues to develop in important ways.
Why Growth Plate Timing Matters
Growth plate closure matters because it influences how much stress a young horse’s skeleton can safely tolerate.
A young horse’s body is designed to move. Turnout, play, and sensible exercise are normal and important parts of development. Bone responds to loading, and appropriate movement supports bone modeling, coordination, and musculoskeletal strength.
However, there is a difference between appropriate developmental exercise and excessive repetitive stress. High-impact work, hard circles, intense speed work, heavy concussion, or workload beyond the horse’s physical readiness can place stress on structures that are still maturing.
Growth plate timing influences:
Training decisions
Conditioning programs
Injury risk
Developmental orthopedic disease risk
Management of young performance horses
Veterinary interpretation of radiographs
Long-term soundness planning
The goal is not to keep young horses inactive. The goal is to match exercise to the horse’s stage of development.
Did You Know? A young horse’s skeleton does not mature all at once. The lower limb generally matures earlier than the upper body and spine. This is one reason that visible height is not the only measure of maturity.
Nutrition and Growth Plate Development
Nutrition has a major influence on growth. Growth plates are active tissues, and they require an appropriate supply of nutrients to function normally.
Important nutritional factors include:
Total calorie intake
Protein quality and amount
Mineral balance
Calcium and phosphorus ratio
Trace minerals such as copper and zinc
Overall growth rate
Body condition
Both overfeeding and underfeeding can be harmful. Excess calories may contribute to rapid growth and increased body weight, placing more stress on developing bones and joints. Poor nutrition may fail to provide the building blocks needed for normal cartilage and bone development.
Research in weanling Thoroughbreds has shown that altered planes of nutrition can affect growth plate cartilage metabolism and structure. In one study, both overfed and underfed horses showed measurable changes in growth plate cartilage compared with horses fed at a balanced level.
This does not mean young horses should be kept thin or undernourished. It means growth should be steady, balanced, and carefully managed.
A growing horse should not be pushed to grow as quickly as possible. Bigger sooner is not always better. A healthier goal is controlled, consistent growth that supports the skeleton, joints, tendons, ligaments, and muscles.
Exercise and Mechanical Load
Bone is living tissue. It adapts to mechanical load, meaning it changes in response to the forces placed upon it.
Appropriate exercise helps young horses develop stronger bones and better coordination. Turnout is especially valuable because it allows natural movement. Foals and young horses that move freely can walk, trot, canter, play, stop, turn, and rest in a self-regulated way.
However, growth plates are not the same as mature bone. Because they are cartilage-based structures, they may be more vulnerable to excessive shear forces, compression, or repetitive overload.
Exercise concerns may include:
Repetitive hard work on firm ground
Excessive forced exercise
High-speed work before adequate conditioning
Sharp turns and tight circles
Heavy workloads in immature horses
Training that does not allow enough recovery time
The best approach is gradual conditioning. Young horses benefit from movement, but intensity should increase slowly and thoughtfully.
Clinical Importance of Growth Plates
Growth plates are clinically important because they can be involved in several problems seen in young horses.
Growth Plate Injuries
Open growth plates are weaker than mature bone in certain ways. Because they are made of cartilage, they can be injured by trauma, twisting forces, compression, or overload.
A growth plate injury can potentially affect future bone growth. Depending on the location and severity, damage to a physis may lead to uneven growth, limb deviation, pain, swelling, or long-term soundness concerns.
Any significant swelling, heat, pain, or lameness in a growing horse should be evaluated by a veterinarian.
Physitis
Physitis is inflammation of the growth plate. It may also be called epiphysitis, although physitis is the more precise term because the physis is the growth plate itself.
Physitis often appears as swelling around the growth plates of long bones. Common areas include regions near the fetlock, knee, or hock. The swelling may be warm or painful, and some horses may show stiffness or lameness.
Physitis is associated with several possible contributing factors, including:
Rapid growth
Nutritional imbalance
Excess energy intake
Obesity or excess body condition
Conformational stress
Hard ground
Excessive exercise
Uneven mechanical loading
Physitis is not always caused by one single factor. It often reflects a combination of growth, nutrition, environment, conformation, and workload.
Osteochondrosis and Developmental Orthopedic Disease
Growth plate health is also part of the larger topic of developmental orthopedic disease, often shortened to DOD.
Developmental orthopedic disease is a broad category that includes abnormal bone and cartilage development in young horses. Conditions within this category may include osteochondrosis, physitis, angular limb deformities, flexural limb deformities, and related developmental problems.
Osteochondrosis involves abnormal cartilage development and failure of normal endochondral ossification in certain areas. It may lead to cartilage flaps, fragments, cyst-like lesions, or joint problems, depending on the location and severity.
Growth plates and joint cartilage are not identical structures, but they are both dependent on healthy cartilage differentiation, ossification, nutrition, and mechanical environment. Problems in these systems can affect long-term soundness.
The study of equine conformation can help you identify angular and flexural limb deformities. Start here:
Recommended books from our library:
Signs That a Young Horse May Need Veterinary Evaluation
Growth and development vary between horses, but certain signs should not be ignored.
Contact a veterinarian if a young horse shows:
Heat near a growth plate
Pain when the area is touched
Sudden swelling near the fetlock, knee, or hock
Stiffness that does not improve
Uneven limb growth
Angular limb deviation
Reluctance to move
Sudden changes in gait
Rapid change in body condition or growth pattern
Early evaluation is important because many developmental problems are easier to manage when they are detected early.
Training Considerations for Young Horses
Growth plate development does not mean every young horse must be kept out of work until every skeletal structure is fully mature. That is too simple and does not reflect how bone adapts to appropriate loading.
Instead, training should be progressive and age appropriate.
Useful principles include:
Build fitness gradually.
Avoid sudden workload increases.
Use good footing whenever possible.
Limit repetitive hard concussion.
Avoid excessive tight circles in immature horses.
Monitor joints and growth plates for swelling or heat.
Keep young horses at a healthy body condition.
Balance turnout, handling, groundwork, and rest.
Work with a veterinarian, farrier, and qualified trainer.
A young horse’s training plan should consider more than age. It should also consider breed, size, growth pattern, conformation, temperament, nutrition, hoof balance, previous injury, and intended discipline.
Did You Know? Growth plates are not just “soft spots” in the bone. They are organized biological structures with distinct zones of cartilage cells. Each zone has a specific job in the process of bone lengthening.
Practical Management Tips for Supporting Healthy Growth
Good growth plate health starts with whole-horse management.
Feed for Balanced Growth
Young horses need high-quality nutrition, but they should not be pushed into overly rapid growth. Work with a veterinarian or equine nutritionist if you are feeding a growing foal, weanling, yearling, or young performance prospect.
Focus on:
Balanced minerals
Appropriate protein
Controlled calories
Forage-based nutrition
Avoiding excessive grain
Monitoring body condition
Adjusting feed as growth rate changes
Encourage Appropriate Movement
Turnout allows young horses to move naturally. This supports bone modeling, muscle development, coordination, and mental health.
Movement is healthy. The concern is not normal movement, but excessive forced exercise or workload that exceeds the horse’s developmental stage.
Watch the Feet
Hoof balance affects how forces travel up the limb. Poor hoof balance can contribute to abnormal stress on joints, growth plates, tendons, and ligaments.
Regular farrier care is especially important in growing horses because the limbs are still developing.
Monitor Growth Spurts
Young horses may go through uneven growth stages. They may look croup-high, narrow, gangly, or temporarily unbalanced. During rapid growth periods, it is wise to monitor workload, nutrition, and limb appearance carefully.
Do Not Ignore Swelling
Swelling near a growth plate should be taken seriously. Some mild developmental changes may resolve with management, but swelling with heat, pain, or lameness needs veterinary attention.
Summary: Key Concepts
Growth plates, also called physes or epiphyseal plates, are cartilage structures that allow bones to lengthen in young horses. They work through endochondral ossification, a process in which cartilage is gradually replaced by bone.
Growth plates close at different times depending on their location. Lower limb structures generally mature earlier, while some parts of the axial skeleton and spine may continue developing much later. This means a horse can look physically mature while still having important skeletal development underway.
Growth plate health is influenced by nutrition, exercise, genetics, hormones, hoof balance, conformation, and overall management. Balanced feeding and appropriate movement support healthy development, while excessive stress, poor nutrition, rapid growth, or abnormal loading may increase the risk of developmental problems.
For owners, the main takeaway is simple: young horses need thoughtful management. They benefit from movement, turnout, good nutrition, regular farrier care, and gradual training.
They also need close observation so early signs of physitis, lameness, or abnormal development are not missed.
Growth plates are small structures with a major role. Protecting them during development can help support a stronger, sounder horse for the future.
Frequently Asked Questions About Growth Plates in Horses
1. What are growth plates in horses?
Growth plates are cartilage regions near the ends of long bones where bone lengthening occurs. They are also called physes or epiphyseal plates. As a horse matures, these cartilage areas gradually turn into bone and close.
2. Why are growth plates important?
Growth plates determine how long bones grow. They are essential for normal skeletal development, limb length, joint alignment, and long-term soundness. Problems affecting growth plates can influence the shape and function of the developing skeleton.
3. When do growth plates close in horses?
Growth plates close at different times depending on location. Some lower limb structures close early, while areas such as the distal radius may close around 2 to 2 1/2 years. Some parts of the spine and axial skeleton may mature later.
4. Can a horse be full height but still not fully mature?
Yes. A horse may reach most of its adult height before every part of the skeleton has fully matured. Height is only one sign of development. Skeletal maturity also involves growth plate closure, bone remodeling, muscle development, and soft tissue conditioning.
5. What is endochondral ossification?
Endochondral ossification is the process by which cartilage is replaced by bone. Growth plates use this process to allow long bones to lengthen during development.
6. What is physitis?
Physitis is inflammation of a growth plate. It may cause swelling, heat, pain, stiffness, or lameness near areas such as the fetlock, knee, or hock. It is most often seen in young, growing horses.
7. What causes physitis in young horses?
Physitis may be associated with rapid growth, nutritional imbalance, excessive calories, hard ground, conformational stress, obesity, excessive exercise, or uneven mechanical loading. It may involve more than one factor.
8. Can nutrition affect growth plates?
Yes. Growth plates are active tissues that require balanced nutrition. Both overfeeding and underfeeding can negatively affect growth and cartilage metabolism. Young horses should be fed for steady, controlled growth rather than rapid weight gain.
9. Is exercise bad for open growth plates?
Not all exercise is bad. Appropriate movement and turnout are important for healthy development. The concern is excessive, repetitive, high-impact, or poorly timed workload that places too much stress on immature structures.
10. When should I call a veterinarian about a young horse’s growth plates?
Call a veterinarian if you notice swelling, heat, pain, lameness, stiffness, uneven limb growth, or sudden gait changes in a young horse. Early evaluation can help prevent small developmental concerns from becoming larger soundness problems.
References
Growth and Bone Development in the Horse: When Is a Horse Skeletally Mature? (MDPI Animals review)
Normal and Abnormal Long Bone Development in Young Horses. Kentucky Equine Research.
Skeletal Maturity in Horses: Growth Plate Ossification and Age Considerations.
The Epiphyseal Plate: Microanatomy and Physiology of the Growth Plate. (Veterinary Specialists CE article)
Endochondral Ossification Overview (ScienceDirect Veterinary Topics).
Effects of Nutrition on Growth Plate Cartilage in Horses. Historical biopsy study (Growth 48:4).
This article is for educational purposes only and does not replace professional veterinary, farrier, nutrition, or training advice. If a young horse shows lameness, swelling, heat, pain, abnormal limb development, or changes in movement, consult a veterinarian.
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