Quote:

At the age of 1 year:
the horse's pasterns have fused

At 18 months:
his cannon bones are mature

At 30 months (2.5 yrs):
he now has stronger - but not entirely mature - knees (the small bones have fused), and his fetlock joints are mature

At 3 years:
the weight-bearing area at the base of the knees is fused, as well as his hindleg between hock and stifle

At 3-and-a-half:
the highest part of his foreleg, the humerus, is fused, as are parts of his femur, the area of his hindleg between stifle and hip

At 4 years:
the shoulder is fused, and the hocks and pelvis are now mature

At 5-and-a-half:
the growth plates over the centrum, which allows the spine to flex, become fused