Objective—To estimate the number of dogs required
to find linkage to heritable traits of hip dysplasia in
dogs from an experimental pedigree.
Animals—147 Labrador Retrievers, Greyhounds, and
their crossbreed offspring.
Procedure—Labrador Retrievers with hip dysplasia
were crossed with unaffected Greyhounds. Age at
detection of femoral capital ossification, distraction
index (DI), hip joint dorsolateral subluxation (DLS) score,
and hip joint osteoarthritis (OA) were recorded. Power
to find linkage of a single marker to a quantitative trait
locus (QTL) controlling 100% of the variation in a dysplastic
trait in the backcross dogs was determined.
Results—For the DI at the observed effect size,
recombination fraction of 0.05, and heterozygosity of
0.75, 35 dogs in the backcross of the F1 to the
Greyhound generation would yield linkage at a power
of 0.8. For the DLS score, 35 dogs in the backcross to
the Labrador Retriever generation would be required
for linkage at the same power. For OSS, 45 dogs in
the backcross to the founding Labrador Retrievers
would yield linkage at the same power. Fewer dogs
were projected to be necessary to find linkage to hip
OA. Testing for linkage to the DLS at 4 loci simultaneously,
each controlling 25% of the phenotypic variation,
yielded an overall power of 0.7.
Conclusions and Clinical Significance—Based on
this conservative single-marker estimate, this pedigree
has the requisite power to find microsatellites
linked to susceptibility loci for hip dysplasia and hip
OA by breeding a reasonable number of backcross
dogs. (Am J Vet Res 2003;222:418–424)
Objective—To determine the radiographic methods
that best predict the development of osteoarthritis in
the hip joints of a cohort of dogs with hip dysplasia
and unaffected dogs.
Animals—205 Labrador Retrievers, Greyhounds, and
Labrador Retriever-Greyhound crossbred dogs.
Procedure—Pelvic radiography was performed when
the dogs were 8 months old. Ventrodorsal extendedhip,
distraction, and dorsolateral subluxation (DLS)
radiographs were obtained. An Orthopedic
Foundation for Animals-like hip score, distraction
index, dorsolateral subluxation score, and Norberg
angle were derived from examination of radiographs.
Osteoarthritis was diagnosed at the time of necropsy
in dogs ≥ 8 months of age on the basis of detection
of articular cartilage lesions. Multiple logistic regression
was used to determine the radiographic technique
or techniques that best predicted development
Results—A combination of 2 radiographic methods
was better than any single method in predicting a cartilage
lesion or a normal joint, but adding a third radiographic
method did not improve that prediction. A
combination of the DLS score and Norberg angle best
predicted osteoarthritis of the hip joint or an unaffected
hip joint. All models that excluded the DLS score
were inferior to those that included it.
Conclusions and Clinical Relevance—A combination
of the DLS score and Norberg angle was the best
predictor of radiographic measures in 8-month-old
dogs to determine whether a dog would have normal
or osteoarthritic hip joints. (Am J Vet Res 2003;64:1472–1478)
Objective—To determine the genetic influence on
expression of traits associated with canine hip dysplasia.
Animals—193 dogs from an experimental canine
Procedure—An experimental canine pedigree was
developed for linkage analysis of hip dysplasia by mating
dysplastic Labrador Retrievers with nondysplastic
Greyhounds. A statistical model was designed to test
the effects of Labrador Retriever and Greyhound alleles
on age at detection of femoral capital epiphyseal
ossification, 8-month distraction index, and 8-month
dorsolateral subluxation score.
Results—The additive effect was significant for age
at detection of femoral capital epiphyseal ossification.
Restricted maximum likelihood estimates (± SD)
for this trait were 6.4 ± 1.95, 10.2 ± 2.0, 10.8 ± 3.1,
11.4 ± 2.1, and 13.6 ± 4.6 days of age for
Greyhounds, Greyhound backcross dogs, F1 dogs,
Labrador Retriever backcross dogs, and Labrador
Retrievers, respectively. The additive effect was also
significant for the distraction index. Estimates for this
trait were 0.21 ± 0.07, 0.29 ± 0.15, 0.44 ± 0.12, 0.52
± 0.18, and 0.6 ± 0.17 for the same groups, respectively.
For the dorsolateral subluxation score, additive
and dominance effects were significant. Estimates
for this trait were 73.5 ± 4.1, 71.3 ± 6.5, 69.1 ± 6.0,
50.6 ± 12.9, and 48.4 ± 7.7%, respectively, for the
Conclusions—In this canine pedigree, traits associated
with canine hip dysplasia are heritable. Phenotypic
differences exist among founder dogs of each breed
and their crosses. This pedigree should be useful for
identification of quantitative trait loci underlying the
dysplastic phenotype. (Am J Vet Res 2002;63: