Nz No Improvment In Hip Scores

[shortstep]

N Z Vet J. 2011 Apr;59(2):67-74.

Trends in the phenotypic hip status of selected breeds of dog as measured by the New Zealand Veterinary Association Hip Dysplasia scheme (1990-2008).

Worth A, Bridges J, Jones G.

Centre for Service and Working Dog Health, Massey University, Private Bag 11222, Palmerston North, New Zealand.

Abstract

AIM: To determine whether there has been improvement in the phenotypic hip dysplasia status in four susceptible dog breeds as measured by the New Zealand Veterinary Association (NZVA) Canine Hip Dysplasia (CHD) scheme.

METHODS: A retrospective analysis of the NZVA CHD database was performed using records of all German Shepherd dogs, Labrador Retrievers, Golden Retrievers and Rottweilers that had undergone evaluation for hip dysplasia between 1990 and 2008. The effect of date of birth on the total hip score was analysed using linear regression, including the covariates of age and gender. When a significant effect of date of birth on total score was noted, ordinal logistic regression was performed to determine the probability of different grades of the Norberg angle and subluxation scores by year of birth; these categories being most indicative of laxity of the coxofemoral joint. Given the known heritability of hip phenotype, determined using radiological measurements, the hypothesis was that if sufficient selection pressure has been applied there would have been a trend towards a lower total score over time.

RESULTS: For Labrador Retrievers (n=1,451), Golden Retrievers (n=896) and Rottweilers (n=313), there was no effect of date of birth on total score over the period of the study (p>0.1). For German Shepherd dogs (n=1,087), there was a significant trend to a lower total score over time (p=0.0003). However the actual size of the effect was small. Ordinal logistic regression on the Norberg angle and subluxation scores for German Shepherd dogs demonstrated a significant lowering of grade in both of these measures of hip laxity.

CONCLUSIONS: This study failed to show significant improvement in the phenotypic hip status of three out of the four most populous large-dog breeds in the NZVA CHD database. Even in the German Shepherd dog, the trend towards a lower total score did not represent a substantial change. Lack of evidence of phenotypic improvement may be due to insufficient selection pressure over the course of the study, selective usage of the scheme (and thus a biased sample), or deficiencies within the NZVA CHD scoring method itself.

CLINICAL RELEVANCE: Greater improvement might be possible if use of the scheme (or an equivalent) is made a compulsory requirement for registration of pedigree breeding stock, if greater selection pressure is applied and/or if pedigree data are included to enable estimations of breeding value.

PMID: 21409732 [PubMed - in process]

[Staranais]

They were discussing this in class the other day. Interestingly, in contrast, the elbow scores in each breed measured have decreased markedly over the same period.

[shortstep]

They were discussing this in class the other day. Interestingly, in contrast, the elbow scores in each breed measured have decreased markedly over the same period.

Elbows are thought to be more strongly 'inherited". ED likely has less risk factors and more direct genes causing the disease. Screening out affected dogs would therefore be more effective in preventing affected offspring. HD likely has more risk factors and maybe even more gene involved. It is more likely a dog could be hips normal but still carry many if not all of the risk factors and genes. Therefore simply screening out affected dogs is not as effective in preventing affecting offspring.

Edited to add, OCD shoulder is thought to be almost all risk factors and trama with very little if any 'disease' genes in play (in some breeds however there may be a different types of shoulder OCD with different causes). Screening has almost no impact on preventing this disease. risk factors inlcude, reckless behaviour, rapid growth, male, trama to joint for either injury or repetitive activites and so forth.

Least that is my story and I am sticking to it! LOL

Edited March 29, 2011 by shortstep

[Staranais]

It's a good story, and I think has a lot of truth to it.

I also think the difference is partly caused by the fact that the NZ elbow scoring system is more highly correlated to disease in a young dog than the NZ hip one is (for OCD and UAP, anyway). Hence, selecting breeding stock on the basis of elbow rads is going to be more effective than selecting on the basis of NZ hip rads.

I would be very interested to see a study on the changing incidence in clinical H.D. cases during this time period (not just the change in radiographic hip scores).

I would also be very interesting to see a study on the changing prevalence of Penn Hip scores based on the population of dogs scored by Penn Hip method.

ETA, I'm not sure if you're right about the OCD. I read all of the recent information I could get my hands on when my own personal dog developed shoulder OCD, and although there has been far less research done on shoulders than elbows or hips, everything I read suggests that although the jury is still out, most specialists think it is rather likely that there is an inherited component to the defective endochondral ossification leading to OCD of the humeral head.

Edited March 29, 2011 by Staranais

[shortstep]

I would be very interested to see a study on the changing incidence in clinical H.D. cases during this time period (not just the change in radiographic hip scores).

Yes, and eeven more interesting if they could break that down into two groups, 1. from parents that were screened and 2. from parents that were not screened.

[shortstep]

Here is the OFA stats for improvment in hip scores over what looks like at least 20 years

http://www.offa.org/stats_hip.html?view=2

OFA elbows by breed, they do not show trends for ED.

http://www.offa.org/stats_ed.html

They do not keep records or track shoulder OCD, though they will read xrays. They offer no breeding directives either.