07/22/2026
Lets talk: Incomplete Ossification
Incomplete Ossification is when small bones in a foal's knees and/or hocks haven't fully developed into hard bone before birth. Instead of being fully mineralized bone, parts of these bones are still soft cartilage.
Those soft bones are responsible for supporting the foal's weight. If a foal with incomplete ossification is allowed unrestricted exercise, those bones can become crushed or permanently deformed under the normal forces of standing and moving. Once this damage occurs, it cannot be reversed and can have lifelong consequences for the foal's soundness and athletic future.
Premature and dysmature foals are at the highest risk, but incomplete ossification can also occur in full-term foals. Because there are often few obvious outward signs, radiographs (X-rays) are the only way to accurately assess whether these bones have matured properly.
Once X-rays are completed, a grading system is used to deteremine the severity:
Grade 1️⃣: Some cuboidal bones have no radiographic signs of ossification.
• Grade 2️⃣: All cuboidal bones show some initial radiographic evidence of ossification, though incomplete.
• Grade 3️⃣: Bones are present but appear small and round.
• Grade 4️⃣: Cuboidal bones have reached adult shapes and sizes
This is why early diagnosis is so important. If incomplete ossification is identified, strict stall rest and careful management are required to protect the developing bones while they continue to mineralize. Unfortunately, foals with severe incomplete ossification (Grade 1–2), are at a much higher risk of developing crushing and irreversible deformity of these bones if they bear weight before they are ready. Once significant damage has occurred, treatment options become limited, the prognosis is often poor, and in the most severe cases, euthanasia may be the most humane outcome.
While incomplete ossification can be a serious diagnosis, identifying it early gives foals the best possible chance. A few weeks of careful management at the start of life can make a huge difference in protecting their future soundness.
For further reading and grade examples: https://vmc.usask.ca/referring-veterinarians/rdvm/nov-2023/research-team-aims-to-update-bone-formation-scoring-system-for-newborn-foals.php
Thanks to Dr. Andrea for the picture (Grade 1-2 with an unfortunate poor prognosis).
