There is always lots of debate as to when to back and ride young horses. As our knowledge of horse anatomy has improved, the reasons against starting early have moved to be based on when growth plates close. I think this is a good thing, as it shows that the industry is beginning to really accept science and use it to improve the welfare of horses. However, I think it is important for people to understand that knowledge of growth plate fusion is not just important for backing horses, but for managing them from birth.
For those of you who are not familiar with growth plates or growth plate fusion, here is a brief summary. A growth plate (epiphyseal plate) is a line of cartilage at the ends of bones. These areas are responsible for bone growth and development. Growth plate fusion, is when the bone stops growing and the cartilage growth plate fuses into bone. In horses, this process starts from the bottom up, with joints in the legs fusing first.
Understanding growth plate fusion and when it occurs in different parts of the body is vital for managing young horses. This is because, until fusion has taken place, we can change or control (to an extent) how the bone grows. Here is a table of when areas go through fusion:
Being able to affect bone growth is usually seen as a negative thing linked to training horses to young. Many racehorses are started before 2 years of age and many go on to have problems with their back in later life, such as kissing or rotated spines and misaligned pelvic problems. This is related to the fact that they are having weight on their back up to 5 years before their spine has stopped growing.
However, many horses have conformational deformities, such as pigeon toe, in later life. Although these problems can be improved by remedial trimming and shoeing, if this problem is addressed while the growth plates are still open, there is a good chance of completely fixing the problem. Therefore a better knowledge of growth plates can help improve the quality of our horses.
I am lucky that our stud at University uses a lot of remedial trimming and sometimes shoeing with the young horses they produce. I have been able to see the before and after results, and understand that if action had not been taken, the problem is often likely to get worse before growth plate fusion, due to the pressure on the bones.