Developmental Orthopaedic Disease (DOD) describes problems affecting the limbs of young horses, including abnormal bone, joint and tendon development. DOD is responsible for major economic losses in the Thoroughbred industry. Investigation into the epidemiology of DOD in Australia and Ireland as described in this thesis has allowed valuable comparisons and recommendations to be made between the studs in these countries.
The project described in this thesis commenced in 1999, with the aim to:
Establish the incidence of DOD on a stud in Australia and to compare this with similar data for a stud in Ireland
To determine relationships between factors affecting severity and incidence of DOD in foals with respect to the country in which they are bred and raised
To further identify risk factor areas associated with the development of DOD
Records of 1717 mares from a major stud in Ireland and another in Australia were made available. Foal weight, age of mare, condition of mare, foal sire and date of birth were monitored over two years. The occurrence of DOD was recorded against these data.
The incidence of DOD was found to be higher on the stud in Australia (average 49.85%) than on the stud in Ireland (average 14%). Foal weight was found to be a significant factor affecting DOD, with heavier foals showing a proportionally higher severity of the problem. The Australian stud had a higher incidence of DOD in 2000 compared to 1999 (65.2% affected vs 32.1% in 1999), whereas the Irish stud had a lower incidence in 1999 compared to 2000 (11.8% affected vs 16.2% in 2000). The dramatic increase in the incidence of DOD in Australian foals over the 1999-2000 period is representative of the increase in a major problem in the industry, as well as greater awareness of the problem over recent years. It highlights the urgent need for further research into understanding the cause(s) of DOD. Overall recommendations arising from the study include that a large scale, long term study be undertaken in Australia. Further investigation into the nutrition of horses in Ireland and Australia would be of great usefulness in understanding DOD, as would possible genetic links. An issue requiring attention is that of developing a standard definition of the disorder. Considering the wide range of disorders which may fit under the umbrella term DOD, a clear definition is of great importance.
The incidence of DOD on one large farm in Ireland was found to be currently low and stable relative to its another large stud farm in Australia. This is a significant finding as the genetic pool of the horses share similarities on both farms, particularly as stallions shuttling between hemispheres sire many foals on both farms. Thus, the data provided herein provide an excellent basis for further valuable comparative studies investigating DOD in foals with a similar genetic background but subjected to differing environmental conditions.