Factors associated with the prevalence of osseous fragments in the limb joints of Hanoverian Warmblood horses

Abstract

Factors associated with the prevalence of osseous fragments (OF) in fetlock and hock joints were investigated in a population of young Hanoverian Warmblood horses selected for sale at auction from 1991 to 1998. The study was based on results of a standardized radiological examination of 3127 horses.

The prevalences of OF in the two joints were significantly dependent on the date, type and quality of the auction, the region of origin and on the anticipated suitability of the horses for dressage and/or show-jumping. The probability of finding OF increased with wither-height. Furthermore, there was a significant association of the individual sire with the prevalence of OF in both fetlock and hock joints, and of the maternal grandsire with the prevalence of OF in the hock joints. Consequently, both non-genetic and genetic parameters should be taken into account in order to reduce the prevalence of OF in young Warmblood riding horses.

Introduction

Locomotory problems are among the major reasons for premature retirement and culling of horses (Philipsson et al., 1998, Wallin et al., 2000). Many chronic conditions of bones and joints can be visualised via diagnostic radiography and recent studies have revealed high prevalences of abnormal radiographic findings in the limbs of active sport horses (Hertsch, 1992, Wallin et al., 2000). Although in some reports the authors were unable to verify the clinical relevance of particular radiographic findings and any negative effect on performance (Grøndahl and Engeland, 1995, Storgaard Jørgensen et al., 1997), horses with radiologically visible alterations are at a higher risk of developing orthopaedic problems than unaffected horses, at least in the long term (Hertsch, 1992). Even subtle gait irregularities caused by musculoskeletal pain can interfere with equine performance (Hertsch, 1992) and manifest lameness may well jeopardise a horse’s further use in competition or racing (Philipsson et al., 1998, Wallin et al., 2000). Accordingly, the radiological state of a horse can have a significant influence on its sale value (Van Hoogmoed et al., 2003).

Intra-articular osseous fragments (OF) are among those radiographic findings that often occur in apparently clinically healthy horses. Development of OF has often been attributed to osteochondrosis syndrome (Jeffcott, 1991). Some failure of normal cartilage maturation might result in the formation of cartilage flaps. After the partial or complete detachment of such flaps, secondary calcification and ossification might take place, characterizing the condition as osteochondrosis dissecans (OCD). However, there is no uniform aetiology of OF in the equine limb joints, i.e., not all OF are attributable to osteochondrosis (Pool, 1993) and trauma could be even more important as a causative factor.

Regardless of their origin, intra-articular OF may also cause secondary changes (such as synovial effusion and the formation of so-called ‘wear-lines’ in the joint cartilage). The extent of such changes and the time of their occurrence largely depends on the type of affected joint (radius of motion), as well as the specific site in the joint (load distribution) and the size and/or number of fragments present (McIlraith, 1993).

Arthroscopic removal of free joint bodies can prevent some or even most of the secondary changes resulting from the presence of intra-articular OF, but joint cartilage lesions must be considered irreversible (Van Weeren and Barneveld, 1999a, Van Weeren et al., 1999b). The primary effort should focus, therefore, on developing prophylactic measures to reduce the prevalence of OF in equine limbs. But effective precaution implies detailed knowledge of the aetiopathology and despite extensive research on osteochondrosis in general, and on equine osteochondrosis in particular, its aetiology is still not completely understood (Gillissen et al., 2003). Environmental effects such as rearing conditions, feeding and exercise have been considered as relevant factors, as have genetic influences (Barneveld and van Weeren, 1999, Bridges and Harris, 1988, Cymbaluk and Smart, 1993, Firth et al., 1999, Glade and Belling, 1986, Jeffcott and Henson, 1988, Mohammed, 1990, Pieramati et al., 2003, Savage et al., 1993, Willms et al., 1999, Winter et al., 1996).

The objective of the present study was to investigate factors associated with the prevalence of OF in the limb joints of young Warmblood riding horses. Environmental effects as well as effects of sire and maternal grandsire were also examined.