Objective—To evaluate whether additive genetic correlations existed between certain aspects of the radiographic appearance of the distal sesamoid (navicular) bones (RNB) or between RNB and other types of radiographic changes in the limbs of Hanoverian Warmblood horses.
Procedures—Quasi-linear and binary traits were defined by the appearance of canales sesamoidales (CSs) and the structure and contour of the forelimb navicular bones (NBs). Prevalences of osseous fragments in the metacarphophalangeal and metatarsophalangeal (fetlock) and tarsocrural joints and deforming arthropathy in tarsal joints were analyzed as binary traits. Genetic parameters were estimated by use of multivariate linear models.
Results—Heritability estimates for the RNB traits ranged from 0.10 to 0.34. Additive genetic correlations among those traits were usually close to unity. Extensive radiographic changes in the NBs, including changes in CSs and alterations in structure and contour, had correlations with less distinct radiographic changes. Negative additive genetic correlations were observed between small numbers of short and conical CSs in the central portion of the distal border of the NB and osseous fragments and arthropathy, and between most types of radiographic findings in the NBs and osseous fragments in tarsal joints.
Conclusions and Clinical Relevance—The genetic bases for different types of RNB were not identical. The detection of correlations between normal RNB and findings of short and conical CSs versus deformed CSs and structural and contour changes warrants further study. Genetically justified distinction between physiologic and pathologic NB changes will increase the efficiency of selecting against NBs with radiographically apparent alterations.
Objective—To determine whether selection
schemes accounting for orthopedic health traits were
compatible with breeding progress in performance
parameters in Hanoverian Warmblood horses.
Procedure—Relative breeding values (RBVs) were
predicted for osseous fragments in fetlock (metacarpo-
and metatarsophalangeal) and tarsal joints,
deforming arthropathy in tarsal joints, and pathologic
changes in distal sesamoid bones. Selection schemes
were developed on the basis of total indices for
radiographic findings (TIR), dressage (TID), and jumping
(TIJ). Response to selection was traced over 2
generations of horses for dressage and jumping ability
and all-purpose breeding. Development of mean
RBVs and mean total indices in sires and prevalences
of orthopedic health traits in their offspring were used
to assess response to selection.
Results—Giving equal weight to TIR and TID, TIJ, or a
combined index of 60% TID and 40% TIJ, 43% to
53% of paternal grandsires and 70% to 82% of
descending sires passed selection. In each case,
RBVs and total indices increased by as much as 9% in
selected sires, when compared with all sires, and
prevalences of orthopedic health traits in offspring of
selected sires decreased relatively by as much as
16%. When selection was exclusively based on TID,
TIJ, or TID and TIJ, percentages of selected sires
were 44% to 66% in the first and 73% to 84% in the
second generation and TID and TIJ increased by 9%
to 10% and 19% to 23%, respectively.
Conclusions and Clinical Relevance—Compared
with exclusively performance-based selection, percentages
of selected sires changed slightly and
breeding progress in TID, TIJ, or TID and TIJ was only
slightly decreased; however, prevalences of orthopedic
health traits decreased in offspring of TIR-selected
sires. (Am J Vet Res 2005;66:1371–1379)