Fine mapping a quantitative trait locus on horse chromosome 2 associated with radiological signs of navicular disease in Hanoverian warmblood horses.

Navicular disease or podotrochlosis is one of the main causes of progressive forelimb lameness in warmblood horses. The objective of this study was to refine a quantitative trait locus on horse chromosome 2 for radiological alterations in the contour of the navicular bone (RAC) in Hanoverian warmblood horses. Genotyping was performed in 192 Hanoverian warmblood horses from 17 paternal half-sib groups. The marker set was extended to 58 informative microsatellites including nine newly developed microsatellites. QTL for RAC could be delineated at 32.50-43.13 Mb and a further new QTL for RAC could be identified at 59.08-65.14 Mb. The markers ABGe342 and ABGe343 reached the highest multipoint Z(mean) and LOD scores at 34.42 and 35.23 Mb with genome-wide error probabilities of P = 0.013 and P = 0.064. In addition, significant associations of markers and haplotypes within the QTL could be shown. The results support the location of the QTL on ECA2 associated with RAC. This work is a further step towards the development of a marker test for navicular disease in Hanoverian warmblood horses.