Discussion

Aims: To measure the incidence of acquired flexural deformity (AFD) affecting the distal interphalangeal joint, (AFDdipj) and unilateral club foot (UCF) in a sample population of Thoroughbred foals. To examine any association between them, to examine other associated factors; including age, between AFDdipj and UCF, laterality, and time of year foaled. Methods: An observational study of Thoroughbred foals (n = 373) on one stud farm was undertaken between 2006 and 2009. The foals were assessed every 3 - 4 weeks prior to routine hoof trimming, recording AFDdipj and UCF. Results: One hundred and sixteen foals (31%) were AFD, 67 (18%) were AFDdipj and 72 (19%) were UCF. The incidence of AFDdipj by age was very significant (Anderson-Darling, s.d. 22.75, P<0.01) mean 53.5 days, median 54.0 days, range 20 - 110 days. The incidence of UCF by age was not significant (Anderson-Darling, s.d. = 39.82, P = 0.092). Twenty-three (33%) AFDdipj foals later became UCF, a highly significant association (P<0.001 by Xsquared). Fifty-four foals (14.47%) were UCF right fore and 18 (4.82%) UCF left fore, a highly significant association of laterality (P<0.001 by Xsquared). Time of year foaled was not significant. Conclusions: In this study, AFDdipj occurred in an earlier and narrower age range than previously thought; AFDdipj foals had a 33% probability of developing UCF, which appears to be associated with laterality and is predominantly a condition affecting the right fore. Practical significance: The incidence of AFDdipj by age is earlier thanprevious literature has stated and therefore the causes of AFD affecting the DIP joint may need to be reassessed. Treatments, such as exercise restriction by box rest and/or intravenous oxytetracycline, need to begin immediately that AFDdipj is recognised. This study has provided useful first time data on these conditions in Thoroughbred foals in the UK, which has challenged previous wisdom.