THE INCIDENCE OF ABNORMAL LIMB DEVELOPMENT IN THE IRISH THOROUGHBRED FROM BIRTH TO 18 MONTHS

A two part survey was carried out in Irish Thoroughbred horses in 1988 and 1989 to establish the incidence and prevalence of developmental skeletal problems, particularly possible manifestations of developmental orthopaedic disease (DOD). Survey One was a retrospective study based on a questionnaire involving the foal crops of 46 stud farms for 3 successive seasons; the 1711 animals initially documented represented 10.46 % of Irish foal registrations. The second survey involved repeated monitoring of the 1988 foal crop from birth to 18 months of age on 17 stud farms. The 248 foals initially examined represented 4.24 % of foal registrations. Treatment for DOD was deemed necessary for 11.3 % of the animals in Survey One. Angular limb deformities and physeal dysplasia ("epiphysitis") together constituted 72.9 % of the cases treated. The peak incidence of DOD problems occurred between weaning and the end of December. More than half the animals treated (53.9 %) recovered completely, ie achieved expected sale value as yearlings, 27.5 % of those treated showed incomplete recovery and mild to moderate loss of sale value and the remaining 18.7 % were killed or lost much of their sale value. In the second survey, while 67 % of animals exhibited some form of DOD, the incidence and severity of problems treated were not significantly different from those of farms in Survey One. Again, physeal dysplasia and angular limb deformity were the predominant clinical conditions and their severity was greatest during the early winter. During the suckling phase colts had a significantly greater incidence of DOD. At all other stages the incidence and severity of DOD was similar in both sexes. However, in the severely affected categories significantly more colts than fillies were killed. There were significant differences amongst stud farms in the incidence and severity of DOD.