690Scientific Reports: Original Study JAVMA, Vol 229, No. 5, September 1, 2006
anine hip dysplasia is a highly prevalent, progres-
sive, and frequently debilitating disease. Its inheri-
tance is quantitative, meaning that its expression can
be influenced considerably by environmental factors.1-4
The prevalence of CHD is as high as 73% in some
breeds of dogs.5Radiographic and clinical evidence of
coxofemoral osteoarthritis is a common sequela of
CHD, especially in older dogs.6,7
It is generally believed that degenerative changes will
develop in joints of all dogs as they age, whereas dogs
with CHD have radiographic signs of osteoarthritis well
before the geriatric period.7Trauma or metabolic dysfunc-
tions are also thought to affect expression of the disease.8,9
One theory of pathogenesis for osteoarthritis is that exces-
sive body weight and the associated increased stress on
joints induce the transformation of passive hip joint laxi-
ty to functional hip joint laxity, thereby initiating
osteoarthritis.10Excessive body weight has been deter-
mined as a risk factor for development of osteoarthritis in
humans, guinea pigs, mice, and dogs.9,11-14Kealy et al have
studied the effects of restricted feeding (and therefore
weight control) on hip joint disease in the same dogs as
reported here and have detected less radiographic evi-
dence of osteoarthritis, compared with control-fed dogs,
at 2 years,155 years,16and 8 years of age.17
The purpose of the study reported here was to
evaluate the effect of food restriction on the develop-
ment of radiographic evidence of osteoarthritis in hip
joints throughout life in Labrador Retrievers.
Materials and Methods
Forty-eight 6-week-old Labrador Retriever puppies
from 7 litters were allotted by pairing to 2 groups of 24 dogs
each.17Two sires and 7 dams were selected from the exist-
ing research populationaon the basis of availability at the
time that litters were required for the study. Both sires and
3 of the 7 dams were determined to be radiographically nor-
mal by use of conventional subjective criteria applied to the
ventrodorsal hip-extended radiograph. The litters were
selected on the basis of availability. Puppies were paired by
litter, sex, and weaning weight prior to random assignment
to a feeding group. Dogs were housed in 2 X 19-m indoor-
outdoor kennel runs with concrete floors, with 1 to 2
pairs/run. The amount of exercise that the dogs had was not
controlled. All dogs were fed the same dry, extruded diet.
One pairmate was fed ad libitum (control fed), and the
other pairmate (restricted fed) was given 25% less of the
same food on a daily basis. Diet and feeding schedules have
been described.15When dogs were 3.25 years old, adjust-
ments were incorporated into the feeding protocol to pre-
vent development of obesity.17
Body weight and body condition scores were monitored
throughout the study. A 9-point scale for body condition
score was used.18
Lifelong diet restriction and radiographic evidence
of osteoarthritis of the hip joint in dogs
Gail K. Smith, VMD, PhD; Erin R. Paster, DVM; Michelle Y. Powers, DVM; Dennis F . Lawler, DVM;
Darryl N. Biery, DVM, DACVR; Frances S. Shofer, PhD; Pamela J. McKelvie, VMD; Richard D. Kealy, PhD
Objective—To evaluate the effects of diet restriction
on development of radiographic evidence of hip joint
osteoarthritis in dogs.
Design—Longitudinal cohort study.
Animals—48 Labrador Retrievers from 7 litters.
Procedures—Forty-eight 6-week-old puppies from 7
litters were paired with littermates by sex and weight,
and each pairmate was randomly assigned to 1 of 2
groups of 24 dogs each. Starting at 8 weeks of age, 1
group was fed ad libitum (control fed) and the other
was fed 25% less (restricted fed) of the same diet for
life on a pairwise basis. The dogs’ hip joints were radi-
ographed in the standard ventrodorsal hip-extended
view at multiple intervals prior to 1 year of age and at
annual intervals thereafter on the basis of birth
anniversary. A board-certified radiologist unaware of
group assignment scored the radiographs for evi-
dence of osteoarthritis.
Results—Prevalence of radiographic evidence of hip
joint osteoarthritis in all dogs increased linearly
throughout the study, from an overall prevalence of
15% at 2 years to 67% by 14 years. Restricted-fed
dogs had lower prevalence and later onset of hip joint
osteoarthritis. Median age at first identification of
radiographic evidence of hip joint osteoarthritis was
significantly lower in the control-fed group (6 years),
compared with the restricted-fed group (12 years).
Conclusions and Clinical Relevance—Restricted
feeding delayed or prevented development of radi-
ographic signs of hip joint osteoarthritis in this cohort
of Labrador Retrievers. Lifetime maintenance of 25%
diet restriction delayed onset and reduced severity of
hip joint osteoarthritis, thus favorably affecting both
duration and quality of life. In addition, the data indi-
cated that development of hip joint osteoarthritis was
not bimodal in these dogs but occurred as a continu-
um throughout life. (J Am Vet Med Assoc 2006;229:
CHDCanine hip dysplasia
From the Department of Clinical Studies, School of Veterinary
Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010
(Smith, Paster, Powers, Biery, Shofer, McKelvie); and Nestle Research
Center, 835 S 8th St, St Louis, MO 63164 (Lawler, Kealy). Dr. Paster’s
present address is Veterinary Medical Teaching Hospital, University
of California, Davis, CA 95616. Dr. Powers’ present address is
Department of Veterinary Clinical Sciences, College of Veterinary
Medicine, Washington State University, Pullman, WA 99164.
Supported by and conducted at Nestlé Purina Company, St Louis, Mo.
Presented in part in abstract form at the Purina Pet Institute
Symposium: Advancing Life Through Diet Restriction, St Louis,
Address correspondence to Dr. Smith.
JAVMA, Vol 229, No. 5, September 1, 2006Scientific Reports: Original Study 691
The dogs were evaluated radiographically by use of gen-
eral anesthesia with the standard ventrodorsal hip-extended
view at 6 intervals prior to age 52 weeks and then at each
birth anniversary for life. The ventrodorsal hip-extended
radiographs were evaluated by a board-certified radiologist
(DNB) for evidence of osteoarthritis.6Specifically, left and
right hip joints of each dog were scored independently on the
basis of sclerosis of the craniodorsal portion of acetabular
subchondral bone, osteophytes on the cranial aspect of
acetabular margin, osteophytes on the caudal aspects of
acetabular margin, and femoral periarticular osteophytes.6,16
Femoral head rimming and the caudolateral curvilinear
osteophyte19were not used as definitive signs of osteoarthri-
tis for this evaluation. The radiographs were marked in such
a way that examiners were unaware of feeding-group assign-
ments. Each dog’s lifelong set of radiographs were evaluated
sequentially and specifically for this study.
Dogs were monitored daily throughout life for signs of
illness and abnormalities. When necessary, appropriate ther-
apeutic measures for various health problems were used,
consistent with established colony protocols and under the
supervision of the attending veterinarian. Health manage-
ment protocols were preestablished for the entire facility.20
Statistical analysis—The Kaplan-Meier product limit
method was used to compare differences in the osteoarthritis-
free interval (difference between groups in time to first diag-
nosis of radiographic evidence of osteoarthritis) between the
control-fed and restricted-fed groups over the lifetime of the
dogs. Linear regression was used to determine goodness of fit
of a line to the age-based osteoarthritis prevalence data.
Significance (P < 0.05) was determined by use of the log-rank
test. All analyses were performed with statistical software.b
Mean ± SD body weights were 24.2 ± 3.79 kg for
the restricted-fed group and 33.7 ± 6.02 kg for the con-
trol-fed group after 8 years of age, as reported. Mean
body weight of the restricted-fed dogs was 26% less
than mean body weight of the control-fed dogs
through 12 years of age.20Mean body condition score
in the restricted-fed group was 4.6, compared with 6.7
in the control-fed group, as reported.20
Among all 48 dogs, the cumulative prevalence of
radiographic evidence of hip osteoarthritis increased
linearly (r2= 0.987; P < 0.001) throughout the study
from 15% (7/48) at age 2 years, 26% (12/46) at age 5
years, and 40% (17/43) at age 8 years to 67% (32/48)
by the end of life (median life span, 11.2 years for con-
trol-fed dogs and 13.0 years for restricted-fed dogs21).
The osteoarthritis-free interval was significantly (P <
0.001) different between groups; median age at first
identification of radiographic hip osteoarthritis was 6
years in the control-fed group and 12 years in the
restricted-fed group (Figure 1).
From age 52 weeks, the difference between the 2
groups in prevalence of osteoarthritis was significant
(Figure 1). At age 2 years, 6 of 24 (25%) control-fed dogs
had radiographic evidence of hip osteoarthritis, com-
pared with 1 of 24 (4%) restricted-fed dogs (Figure 2).
At age 5 years, 9 of 23 (39%) dogs in the control-
fed group had radiographic evidence of hip
osteoarthritis, compared with 3 of 23 (13%) dogs in
the restricted-fed group. At age 8 years, 14 of 22 (64%)
dogs in the control-fed group had radiographic evi-
dence of hip osteoarthritis (2 dogs died before the age
of 8 years), compared with 3 of 21 (14%) dogs in the
Cumulatively, by 14 years, 83% (20/24) of the con-
trol-fed group had developed radiographic evidence of
hip osteoarthritis, compared with 50% (12/24) of the
Initial phenotypic expression of CHD is recog-
nized radiographically as femoral head subluxation on
the hip-extended ventrodorsal radiographic projection
that has been regarded as a standard, albeit, in our
opinion, with minimal scientific support. Hip joint lax-
ity and femoral head subluxation, if functional, induce
pathologic consequences that include abnormal load-
ing during weight bearing, leading to cartilage damage
and bone remodeling. The end result of this self-per-
petuating cycle of abnormal loading and remodeling is
classical osteoarthritis characterized by synovitis,
increased joint fluid, joint cartilage erosion, elongation
and edema of the round ligament, thickening of the
joint capsule, and osteophyte formation.9,22,c
In the present study, restricted feeding had a pro-
found effect on the radiographic hip phenotype of the
Labrador Retrievers. The onset of osteoarthritis was
delayed among the restricted-fed dogs, compared with
Figure 1—Results of Kaplan-Meier analysis for proportion of
Labrador Retrievers (gray line = restricted-fed dogs [n = 24];
black line = control-fed dogs ) without radiographic evidence
of hip joint osteoarthritis.
Figure 2—Cumulative prevalence of hip joint osteoarthritis in the
same dogs as in Figure 1.
692 Scientific Reports: Original Study JAVMA, Vol 229, No. 5, September 1, 2006
control-fed pairmates. The paired feeding regimen was
designed into the study, with stratification by weight
and sex within litter, to minimize genetic differences
among subjects as much as possible while allowing
amount of diet fed to be the major variable. Prevalence
of osteoarthritis in the present study was slightly dif-
ferent from that of earlier evaluations of the same
dogs.15-17 This discrepancy was attributable to the fact
that radiographs were scored by the same radiologist at
different times for annual evaluations for the earlier
reports and later for longitudinal evaluations.
Radiographs for this study were rescored to avoid
introducing an early-late learning bias. Differences
among the reports were minor and did not affect con-
clusions of the studies.
Longitudinal studies are essential to understand-
ing the true biological behavior of complex diseases
such as CHD and osteoarthritis. To the authors’ knowl-
edge, no similar studies have been published other
than previous reports15-17of these dogs. Of particular
interest and importance is the observation that radio-
graphic evidence of osteoarthritis increased in preva-
lence long after age 1 to 2 years, which has been the
accepted conventional age for radiographic evaluation
for hip dysplasia. The concept of accurate hip screen-
ing by 2 years of age was originally proposed by Jessen
whose data suggested that hip
osteoarthritis and radiographic evidence of joint laxity
have no appreciable incidence after 2 years of age,
negating the need for hip evaluation later in life. This
concept (use of 1 to 2 years of age as the accepted con-
ventional age for hip screening) was subsequently
adopted for hip-screening methodologies around the
world.24-27However, the linear increase in prevalence of
osteoarthritis over the life of the Labrador Retrievers in
the present study refutes the conventional dogma that
hip joint osteoarthritis occurs only early in life in dogs
with CHD. Rather, a constant rate of development of
radiographic changes was indicated by our data.
Diet restriction extends life span in a wide variety
of vertebrate and invertebrate species.22Moreover,
studies28-32of diet restriction in mammals such as rats,
mice, and primates also reveal that increased longevity
is associated with delay or prevention of species- and
The association between body mass and the onset
and progression of osteoarthritis has been reported in
species other than dogs, such as guinea pigs and
humans.12,13Thirty-three percent of osteoarthritis in the
peripheral joints of women can be attributed to effects
of obesity.33Obese women and men have 4- to 4.8-
times increased risk, respectively, for developing
osteoarthritis, compared with nonobese women and
men.33Excessive body weight also has been associated
with the onset of degenerative joint disease in the hock
joints of broiler fowl fed ad libitum, compared with
restricted-fed broiler fowl and a lighter fowl strain.32In
addition, proteoglycan synthesis is decreased and
degradation is increased in the joints of ad libitum–fed
fowl, indicating impaired repair of articular cartilage.32
Although the mechanism by which degenerative joint
disease is mitigated by diet restriction is unclear, part
of the explanation might be associated with responses
that antagonize the transition from passive joint laxity
to the more pathologic functional joint laxity that ulti-
mately leads to osteoarthritis, perhaps modulated by
inflammatory mediators.34,35In any event, the effects of
restricted energy intake are consistent in many species.
Dogs vary considerably with respect to individual
energy requirements; therefore, it is not feasible to spec-
ify a universal energy intake to achieve the benefits
observed in the restricted-fed dogs of the study reported
here. However, it is recommended that lean body con-
formation (body condition score of 4 or 5)18be main-
tained by use of appropriate caloric restriction in adult
dogs and in growing puppies after age 8 weeks to maxi-
mize the opportunity to potentially delay or prevent
development of many diseases of aging,20,28-31including
coxofemoral osteoarthritis associated with CHD.20The
present study examined restricted feeding for life; there-
fore, the impact of short-term diet restriction or other
feeding regimens on development and progression of
osteoarthritis is unknown and may be different. Effects
of restricted feeding in dogs of breeds not susceptible to
CHD or not as susceptible as Labrador Retrievers were
not determined in this study and may also be different.
The recognition that development of osteoarthritis
in CHD-susceptible dogs is linear into late life and not
bimodal is a new observation with important implica-
tions, including clinical relevance for practicing veteri-
narians, orthopedic surgeons, dog breeders, and pet
owners. Results of this study refute the findings of
Jessen and Spurrell,23who reported that the osteoarthri-
tis of CHD does not occur after 2 years of age. In fact,
the prevalence of osteoarthritis was linear over the life
span of these Labrador Retrievers, suggesting that onset
of CHD can occur at any age, and raising serious con-
cerns over the accuracy of conventional hip-extended
radiography at 1 or 2 years of age. Hip phenotype can
change markedly (from normal to abnormal) after 2
years of age. Breeds of dogs with high susceptibility to
CHD should be kept lean for life, and dogs selected for
breeding should have radiographic hip evaluations at
regular intervals throughout life. We suggest that more
exacting methods than use of the hip phenotype obtained
from the standard hip-extended radiographic view should
be used for selection of breeding candidates.36
Nestle (Ralston) Purina Research, Gray Summit, Mo.
SAS, version 8.2, SAS Institute Inc, Cary, NC.
Riser WH. Hip dysplasia in military dogs (abstr), in
Proceedings. Canine Hip Dysplasia Symp Workshop 1973;131.
1. Jessen CR, Spurrell FA. Heritability of canine hip dysplasia,
in Proceedings. Canine Hip Dysplasia Symp Workshop 1973;53–61.
2. Henricson B, Norberg I, Olsson SE. On the etiology and
pathogenesis of hip dysplasia: a comparative review. J Small Anim
3. Hedhammer Å, Olsson S-E, Andersson SÅ, et al. Canine hip
dysplasia: study of heritability in 401 litters of German Shepherd
Dogs. J Am Vet Med Assoc 1979;174:1012–1016.
4. Hutt FB. Genetic selection to reduce the incidence of hip
dysplasia in dogs. J Am Vet Med Assoc 1967;151:1041–1048.
5. Paster ER, LaFond E, Biery DN, et al. Estimates of preva-
lence of hip dysplasia in Golden Retrievers and Rottweilers and the
influence of bias on published prevalence figures. J Am Vet Med Assoc
JAVMA, Vol 229, No. 5, September 1, 2006Scientific Reports: Original Study 693
6. Owens J, Biery D. Coxofemoral joints and pelvis. In: Cann
CC, Hayes LAK, eds. Radiographic interpretation for the small animal
clinician. 2nd ed. Baltimore: The Williams & Wilkins Co, 1999;82–89.
7. Morgan JP, Wind A, Davidson AP. Hereditary bone and
joint diseases in the dog: osteochondroses, hip dysplasia, elbow dys-
plasia. Hannover, Germany: Schlutersche GmbH and Co, 2000;
8. Lust G, Rendano VT, Summers BA. Canine hip dysplasia:
concepts and diagnosis. J Am Vet Med Assoc 1985;187:638–640.
9. Smith GK, Popovitch CA, Gregor TP, et al. Evaluation of
risk factors for degenerative joint disease associated with hip dyspla-
sia in dogs. J Am Vet Med Assoc 1995;206:642–647.
10. Kapatkin AS, Fordyce HH, Mayhew PD, et al. Canine hip
dysplasia: the disease and its diagnosis. Compend Contin Educ Pract
11. Popovitch CA, Smith GK, Gregor TP, et al. Comparison of
susceptibility for hip dysplasia between Rottweilers and German
Shepherd Dogs. J Am Vet Med Assoc 1995;206:648–650.
12. van Saase JL, Vandenbroucke JP, van Romunde LK, et al.
Osteoarthritis and obesity in the general population. A relationship
calling for an explanation. J Rheumatol 1988;15:1152–1158.
13. Bendele AM, Hulman JF . Effects of body weight restriction
on the development and progression of spontaneous osteoarthritis in
guinea pigs. Arthritis Rheum 1991;34:1180–1184.
14. Wilhelmi R, Maier R. Beobachtungen uber den einflub von
druckbelastung und bewegung awf die gelenke am modell
arthrosedisponieter mause. Akt Rheumatol 1987;12:161–167.
15. Kealy RD, Olsson SE, Monti KL, et al. Effects of limited
food consumption on the incidence of hip dysplasia in growing dogs.
J Am Vet Med Assoc 1992;201:857–863.
16. Kealy RD, Lawler DF , Ballam JM, et al. Five-year longitudi-
nal study on limited food consumption and development of
osteoarthritis in coxofemoral joints in dogs. J Am Vet Med Assoc 1997;
17. Kealy RD, Lawler DF , Ballam JM, et al. Evaluation of the
effect of limited food consumption on radiographic evidence of
osteoarthritis in dogs. J Am Vet Med Assoc 2000;217:1678–1680.
18. Laflamme D. Development and validation of a body condi-
tion score system for dogs. Canine Pract 1997;22:10–15.
19. Powers MY, Biery DN, Lawler DE, et al. Use of the cau-
dolateral curvilinear osteophyte as an early marker for future devel-
opment of osteoarthritis associated with hip dysplasia in dogs. J Am
Vet Med Assoc 2004;225:233–237.
20. Kealy RD, Lawler DF , Ballam JM, et al. Effects of diet restric-
tion on life span and age-related changes in dogs. J Am Vet Med Assoc
21. Lawler DF , Evans RH, Larson BT, et al. Influence of lifetime
food restriction on causes, time and predictors of death in dogs. J Am
Vet Med Assoc 2005;226:225–231.
22. Olsson S-E, Kasstrom H. Etiology and pathogenesis of
canine hip dyplasia: introduction of a new concept, in Proceedings.
Am Vet Med Assoc Symp Hip Dysplasia 1973;1–52.
23. Jessen CR, Spurrell FA. Radiographic detection of canine
hip dysplasia in known age groups, in Proceedings. Canine Hip
Dysplasia Symp Workshop 1972;93–100.
24. Gibbs C. The BVA/KC scoring scheme for control of hip
dysplasia: interpretation of criteria. Vet Rec 1997;141:275–284.
25. Scientific committee: hip dysplasia—international certificate
and evaluations of radiographs. Helsinki: Federation Cynologique
26. Olsson SE. Advice and directions for Roentgen examination of
the hip joints of German Shepherd Dogs. Hundsport 1961;suppl:1–4.
27. Keller G. Hip dysplasia, a guide for dog breeders and owners.2nd
ed. Columbia, Mo: Orthopedic Foundation for Animals Inc, 1989;1–28.
28. Weindruch R, Walford R. The retardation of aging and dis-
ease by dietary restriction. Springfield, Ill: Charles C. Thomas,
29. Lane M, Black A, Ingran D, et al. Calorie restriction in non-
human primates: implications for age-related disease risk. J Anti
Aging Med 1998;1:315–326.
30. Masoro E. Dietary restriction and aging. J Am Geriatr Soc
31. Bodkin N, Alexander T, Ortmeyer H, et al. Mortality and
morbidity in laboratory-maintained rhesus monkeys and effects of
long-term dietary restriction. J Gerontol 2003;58A:212–219.
32. Venkatesan N, Thorp B, Hulmes D. Articular cartilage pro-
teoglycan metabolism in avian degenerative joint disease: effects of
strain selection and body weight. Connect Tissue Res 1999;40:199–208.
33. Felson D. The epidemiology of osteoarthritis in the periph-
eral joints: does excess weight cause osteoarthritis and, if so, why?
Ann Rheum Dis 1996;55:668–670.
34. Hegemann N, Wondimu A, Kohn B, et al. Cytokine profile
in canine immune-mediated polyarthritis and osteoarthritis. Vet
Comp Orthop Traumatol 2005;18:67–72.
35. Fernandes JC, Martel-Pelletier J, Pelletier JP. The role of
cytokines in osteoarthritis pathophysiology. Biorheology 2002;39:
36. Smith GK, Gregor TP, Rhodes WH, et al. Coxofemoral joint
laxity from distraction radiography and its contemporaneous and
prospective correlation with laxity, subjective score, and evidence of
degenerative joint disease from conventional hip-extended radiogra-
phy in dogs. Am J Vet Res 1993;54:1021–1042.