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Retrospective cohort study of changes in hip joint phenotype of dogs in the United States.

OBJECTIVE
To determine whether there had been a significant improvement in hip joint phenotype of dogs in the United States by comparing results of evaluations done by the Orthopedic Foundation for Animals of dogs born between 1972 and 1980 with those of dogs born between 1989 and 1992 and determining whether there had been an increase in the percentage of dogs classified as having excellent hip joint phenotype.


DESIGN
Retrospective cohort study.


SAMPLE POPULATION
270,978 evaluations.


PROCEDURE
Numbers and percentages of dogs classified as having excellent hip joint phenotype during each period and change between periods in percentages of dogs classified as having excellent hip joint phenotype were calculated.


RESULTS
Percentage of dogs born between 1989 and 1992 that were classified as having excellent hip joint phenotype (15,289/143,668; 10.64%) was significantly higher than percentage of dogs born between 1972 and 1980 that were classified as having excellent hip joint phenotype (9,960/127,310; 7.82%). The increase in percentage of dogs classified as having excellent hip joint phenotype was significantly higher for male (51%) than for female (27%) dogs.


CLINICAL IMPLICATIONS
Results suggest that there has been an improvement in the hip joint phenotype of dogs in the United States between the 1970s and early 1990s and that the improvement has been greater among male than among female dogs.