Racehorses need strong bones and stable joints to remain healthy throughout their careers. But some premature foals are born with just the opposite: soft bones and joints at risk of collapse. Can these at-risk newborns with so-called incomplete ossification beat the odds and turn into successful racehorses?

Lillian M.B. Haywood, VMD, recently completed a study aiming to answer that question and presented the results at the 2015 American Association of Equine Practitioners’ Convention, held Dec. 5-9 in Las Vegas. Haywood is an ambulatory practitioner at Rood & Riddle Equine Hospital, in Lexington, Kentucky.

Haywood said that incomplete ossification (essentially, cartilage hasn’t completely hardened into bone before birth) of the cuboidal bones, located in the tarsus (hock) and carpus (knee), can potentially have lifelong consequences. If those bones are incompletely formed, the joints cannot hold up to the foal’s weight or movement. This can lead to joint damage, especially crushing and wedging of the bones in the tarsus, and predispose the foal to unsoundness as he ages.

Haywood and colleagues hypothesized that foals with a shorter gestation length and incomplete cuboidal bone ossification would be less likely to race and would earn less than their maternal siblings. To find out, the team conducted a retrospective study in which they evaluated medical records from 1994 to 2011 of foals younger than 90 days of age with tarsal radiographs. They reviewed those radiographs and graded the ossification based on the Adams Skeletal Ossification Index (a four-point scale where Grade 1 reflects no evidence of ossification and Grade 4 reflects normal ossification), and also made note of the length of each foal’s gestation. Then, the team compared each foal’s race records to those of their maternal siblings