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Battle of Theories

I've read and thought about these two quite a bit.  (This article only examines numbers for Swissies.  These numbers do not apply to other breeds.)  I've done some number crunching. For once I'm actually putting what I learned in school to good use.  Looked at it from a scientific view as if OFA (Orthopedic Foundation for Animals) and PennHip were two competing theories. And like all other theories, they aren't perfect. They tend to make broad suggestions about changing the world. 

OFA has his advantages and disadvantages. Advantages being that you get a grade (excellent, good, fair, etc...), and dogs do not get rated unless x-rays are done after 2 years of age. This is not to say that hips can't fall apart after 2 years. Disadvantages are that it is much more subjective, ratings on the same dog can change. There is also that option of keeping your dog awake which affects accuracy of the x-ray. 

PennHip on the other hand is a statistic. It tells you "how loose" the hips are (measured by a distraction index, DI), which are correlated with hip problems. There is no chart on the correlation between PennHip and degenerative joint disease, DJD, for Swissies, but there is one for Rotties, which are similar in size/structure. If you look at the distraction indexes that Swissies have gotten (mean at .55 and looking at ranges on the health database), most have anywhere between 5% and 40% chance of developing DJD. Those odds are better than raw chance (50%). Surprise! 


However, I'm guessing from the available DI and percentile information, the distribution of Swissy distraction indexes is leptokurtic, peaks high and narrow. In short, it means that dogs who are slightly tighter than average will be in the high percentiles. Dogs who are slightly looser than average will be in the low percentiles. PennHip never implies that the issue is corrected nor do I known if there are enough Swissies that have done PennHip to fix the issue. 

But if you look at the mean PennHip score, it is right at 20% risk of developing DJD, which is the same statistic that OFA gets for hip dysplasia (19% of Swissies have abnormal hips). That should make you feel better in terms of number crunching. 

As far as correlations between PennHip and OFA reports, it seems pretty low. From my point of view, PennHip doesn't have much predictive power unless you have a dog in the top 10-20% in Swissies ONLY.  Pennhip scores in the 0-80% tile don't mean much of anything.  Dogs in the 20% have OFAed as Good, and Dogs in the 60% have failed OFA.  This is even true of other breeds.  I've heard of border collies who have OFAed in the 80% but still failed OFA.  If PennHip was really going to improve the frequency of hip problems, for Swissies, they should advocate breeding ONLY dogs in the top 20%.  Otherwise, predictive power is loss and the numbers are meaningless.  However, this is somewhat unrealistic, so OFA is another option for health clearances.   

It boils down to doing OFA (that is highly subjective and does not provide any predictive value) or doing PennHip (provides you with some sort of an idea, but since correlations are pretty low, it is more unreliable than OFA's subjectiveness). Layman's terms - OFA tells you whether or not your dog has dysplasia, but not the likelihood of your dog developing it. PennHip tells you the chances your dog might develop hip problems, but not an absolute yes or no. And keep in mind there are dogs who have tight hips according to PennHip and moderate hip dysplasia. And there are dogs who have excellent OFA rated hips, but loose according to PennHip

I wouldn't say that one is better than the other. They are both very different in methods and interpretation. In a perfect world, since Pennhip uses an OFA view, you could also get an OFA rating at the same time. Then it would only help us understand how to evaluate breeding stock better. Then again, it is probably like asking Biologists and Sociologists to play nice.
 

Update: 1.18.2015

 

With new data available to Greater Swiss Mountain Dogs and as my own Mouse ages, I put some thinking into this topic again. Part I :At 12.5 years old, I took Mouse in for his senior checkup along with x-rays to see how he is doing. He's moving slower and weaker, but nonetheless pretty happy. He's been on adequan, acupuncture, supplements, and swimming when we can. Much to my surprise, three different vets at three different clinics confirmed that he was free of hip dysplasia and arthritis at 12.5 years old.

 

Mouse had pre-limed at Good and he rated a Fair at two years old. I was pretty thrilled that his hips were still in good condition at a ripe old age, and his breeder insisted that it was environmental at that point. While I can't take complete credit, I am a strong believer that the impact of our environment (nurture) is very strong. In humans, it is suspected that 90% of our long-term health outcomes are due to environmental factors! You can watch this TED talk by Dan Buettner on Blue Zones for more information.

 

He swims at North Padre Island at 12.5 years old.

 

I won't say that what I did is what everyone should do. Try a few things out. If it seems to work, persist. If not find something else. Here's the short version of the things that worked for Mouse: 1. A job or activity he loves (therapy dog). That's true for humans too. There's plenty of research on mortality after retirement. 2. Exercise: Swimming, swimming, swimming. Short walks, backing up, cavalettis (4 inches off the ground), and holding a stand with only three legs. 3. Supplements: Tumeric, Phytofex (includes glucosamine and chondrotin), coconut oil, vitamin b and e, fish oils, and coconut oil. 4. Quality Food. Feed something that works well, and keep your dogs lean. 5. Adequan. For his weight, he gets 2.5 ccs every four weeks. There's also a loading dose period of adequan. 6. Acupuncture every other week. 7. Massage time. On days he's at home with me, we have Mommy and Mouse massage time

 

Part II: Recently, someone posed this question: "If my breeding program produces mostly healthy hips, what else can I do?" Since I'm not a breeder in the traditional sense (I've yet to have a litter on the ground as of today), I can only use the available data to evaluate what is going on in my breed.

When I wrote the first part of this page sometime in the mid-2004, I went through OFA's database and our breed's online database (which since our national club has removed from public view.) People could submit PennHip to the national club at the time. I also called around, and many people told me what scores their dogs got. Of course, it was really easy to see which dogs had failed OFA Hips, and decided to make their PennHip scores instead. They'd have all passing OFA clearances except Hips, and their PennHip scores on personal websites.
 

What I'm actually seeing in my breed is improvement of hip scores on submitted dogs. If you look at failure rates within litters, it tends to be the dogs that are overweight who fail. Our breed, like the majority of overweight American pets, is currently being plagued by the obesity issue. In the conformation ring and pets on the couch are both fairly overweight in my opinion. However, I have a fairly specific definition of fit dogs. I like my dogs to function like athletes.

 

My personal opinion on what's going on in my breed is that health-focused breeders are improving hip scores from a genetic perspective, but owners who do not grow their puppies slowly and keep them heavy may see higher risks of hip dysplasia. My interpretation is that if you finding success in your breeding practices, keep doing what you're doing and make sure your puppy buyers don't keep their dogs heavy. Breeders focus on genetics, and the dog owners should be focusing on environment once the puppy is in their hands.


To investigate this more: I went through our Greater Swiss Mountain Dog health survey (http://www.offa.org/surveys/survey_swissy.html), and found some great answers to the OFA vs. PennHip issue. 1225 dogs were submitted in the survey. Of the dogs that are submitted for OFA in our breed (498 total) , only about 28% of them do some other hip evaluation. Of the other hip evaluations available, only 63 also did PennHip. Only about 13% of all dogs OFAed also had PennHip done. Of the dogs in the survey who had OFA hips done, 92% of dogs were passing (excellent, good, or fair)!

From all the Swissies in the survey, only ~4.2% reported to have hip dysplasia. That's 51 dogs out of the 1225 dogs in the survey.   Of course, this survey is still only a subset of all Swissies. There could certainly be dogs that are not in the survey, not diagnosed, or passed due to other issues. Despite that, these are still pretty good numbers. This is very exciting for our breed.
 

However, breeders are left with a different dilemma, do they breed to what looks good at two years old or do they breed to longevity in health? We sure do hope that the two are correlated. Taking hip health to another level could mean not only breed to dogs that passed at two years old, but also would look for pedigrees that maintained that hip health far after the dogs are retired. *Hip health is only one aspect of canine health. Many other considerations should be made when making breeding decisions. You're not just breeding to a dog's hips. You're breeding to the entire dog.


Mock up of social graphs I can make.

 

I have a small obsession with data visualization, and if you (the reader) had data on your breed and a particular health issue, I could plug it into something like the graph above - with clusters for each pedigree in your breed and color coding the health issue. Green are not affected, and red are affected. It would be very easy to visually see which pedigrees were throwing what and which combinations of pedigrees were successful. If I could find the time, I could scrape the data from OFA and plug it in myself. Or OFA could be really nice and just sent it to be in data file. :o)

 

 

New: Post I made on Show-Dog L - OFA vs. PennHip article below (sometime around 2006).

A while back, there was debating on the merits of OFA and PennHip. I decided to do an investigation on the results, meaning, and generalizability of both methods in regards to my breed.

I'm formally trained in statistics specializing in hierarchical multi-group and nested modeling. Playing with numbers is something I do on a regular bases, and yes, I love it.

I analyzed the methods and results of both methods and wrote up a short article based mostly on statistics. Full article in on my website. What I found in my breed (using a similarly built and sized breed which PennHip has a large amount of data on a reference group) regarding PennHip was that Distraction indices in my breed were fairly narrow (little variation). Also, the majority of the dogs PennHipped had passed OFA ratings.

The majority of dogs in our sample for my breed had a distraction index that would be correlated to no DJD. In statistics, little variation is a very, very bad problem that could be due to sampling error (self-selection in this case) as well as a variety of other things. Dogs (using the reference breed of similar size and build) had the 50%-tile mark had equal chance of dogs who were OFAed of developing HD - which is 20% of the breed. This interpretation is good for both PennHip and OFA because it shows that both methods are reliable measures. This is bad however for people who assume that all dogs PennHipped over the 50%-tile mark has no chance of developing HD.

What did this mean in terms of statistics? To me, it means that PennHip in my breed basically doesn't tell you anything unless the dog was at 80%-tile or higher. At 80%-tile, the reference breed had little to no chance of developing HD.

OFA also has inherent problems from age of HD development (if after age 2), objectivity, quality of x-rays, etc...

Keep in mind that OFA and PennHip is based on research, to which neither side will admit flaws in their methodology or setbacks in their analyses. Being in biobehavioral research, I know that all too well. Scientists will defend their theories until death, and sometimes even from beyond the grave.

Anyways, my interpretations only generalize to my breed. If you would like for me to examine PennHip statistics for your breed, I'd be more than happy to do so.