Effect of inbreeding on the "Club Foot" disorder in Arabian Pureblood horses reared in Italy

Abstract

Background: "The Club Foot" (or "Mismatched Foot") is an acquired or congenital flexural deformity of the distal interphalangeal joint, caused by a shortening of the musculotendinous unit of the deep digital flexor tendon.

Aim: The aim of this research was to detect the incidence of the disorder in Arabian Pureblood horses, attempting to understand its causes and to analyze a possible role of inbreeding in its expression. In this breed, in fact, the pathology is widespread because in the environment of origin, the rocky desert, a hard and almost goat's hoof is not disabling so the selection against this disorder has never been done.

Methods: Pedigrees were taken from 141 (reference population = RP) adult Arabian Pureblood horses (51 males and 90 females) belonging to eight Italian different farms during the period 1982-2017. For each horse, the presence or not of the disorder was observed and inbreeding coefficients (F) was performed. Four grades of deformity were considered. Moreover, the environmental condition of each farm was considered: boxes, paddocks, nutrition, orientation, and hoof care and shoeing. The chi-square test was applied. Analysis of variance (ANOVA) was used to test the differences in the average inbreeding coefficient (F) between affected and healthy animals, between sexes and between shod and unshod animals.

Results: Two grades of deformity were observed (I and II) which give less severe manifestations, with 28 females and 25 males (37.59% of the examined horses) showing the disorder. No differences between males and females or between shod (38.29%) and unshod (61.70%) were observed. Environmental conditions do not influence the rate of pathology in the different farms, with a prevalence of the disorder ranging from 7.69% up to 100% on farm. The whole population (WP = RP and its genealogy) included 3,355 records subdivided in seven traced generations. One hundred and eighteen out of 141 horses (RP) were inbred (83.69%). The average inbreeding coefficient (F) in the RP was 0.095. Inbreeding coefficient in RP was <0.05 in only 15 horses (12.71% of inbred), whereas it was >0.25 in 28 horses (23.73% of inbred).

Conclusion: High inbreeding coefficients were observed in all farms and in particularly in affected animals suggesting that high inbreeding coefficients increases the probability that the disorder occurs. Future works may include the study of the hereditability of the character, and the attempt to identify loci associated with the disorder.

Keywords: Arabian Pureblood horses; Club Foot disorder; Inbreeding; Incidence.

Fig. 1.. Graphical representation of a pedigree of one affected male of farm 5.