Osteochondrosis and osteochondral fragments in Standardbred trotters: prevalence and relationships

Developmental orthopaedic diseases (DOD) such as osteochondrosis (OC)/osteochondrosis dissecans (OCD), palmar/plantar osteochondral fragments (POF), ununited palmar/plantar eminences (UPE) and dorsoproximal first phalanx fragments are well recognised in the horse. Aetiopathogeneses are controversial and molecular genetic screening of DNA has recently been employed for their elucidation. Precise phenotypic definition and knowledge of breed-specific prevalence and interrelations are essential for the interpretation of following genomic studies in Standardbred trotters.

To assess the prevalence, trend of development and interrelation of DOD in tarsocrural, metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in Standardbred trotters.

The tarsocrural and MCP/MTP joints of 464 Norwegian Standardbred yearlings were radiographed and the prevalence and interrelation of osteochondral lesions calculated.

Osteochondral lesions were diagnosed in 50.7% of the horses. The prevalence of tarsocrural OC/OCD at the distal intermediate ridge of the tibia (DIT) and the lateral trochlear ridge of the talus (LTT) was 19.3%. The prevalence of OC/OCD in MCP joints was 3.6%, whereas those of POF and UPE in MCP/MTP joints were 23.1 and 3.9%, respectively. Interrelation was evident for 1) most equivalent lesions in joint homologues, 2) OCD DIT and OCD LTT and 3) POF and UPE. Lesions in hock and fetlock joints were generally not significantly associated.

The prevalence of tarsocrural OC/OCD in Norwegian Standardbreds is apparently increasing, whereas that of other articular DOD appears stable. Association analyses verify bilateralism for most equivalent lesions and suggest aetiological resemblance also between other lesions. The absence of a significant association between tarsocrural OCD and POF implies that the lesions must be considered statistically different disorders.

The prevalence results emphasise that DOD should be considered in Standardbred breeding regimens (e.g. by sire selection subsequent to progeny testing). Also, improved phenotypic definitions will help elucidate the true causal genes in following genomic studies.