“Weighing the pig won’t make it fatter”: my latest “Best of Health” article

Best of HealthMost of us who have lived with and bred dogs for many years would like to think we’re pretty aware of potential and actual health problems in our breed. We’d therefore be pretty confident that any Breed Health Survey would simply confirm most of what we already know. Generally speaking, that’s what happens in practice.

In Dachshunds, we have now carried out a “quick and dirty” survey at one of our Breed Conferences and 3 more extensive paper and online ones; our 3-yearly DachsLife surveys.

Unsurprisingly, every previous survey showed IVDD to be the most prevalent health condition in Dachshunds. They also confirmed most of the things we already knew about anecdotally, including some conditions that breeders have been reluctant to be open about. Overall, the reported data confirmed that the issues we have prioritised as a Breed Council were indeed the right ones.

Interestingly, this year we found that Ear Mites, problems with Anal Glands and adverse vaccine reactions had a higher prevalence than conditions such as Diabetes and Patellar Luxation which some people had mentioned as being an issue. So, sometimes the data helps dispel the urban myths and in other cases flags up some surprises.

One of my favourite quotes in relation to measurement is that “repeatedly weighing a pig won’t make it fatter”. So, in our case, yet more measurement of disease prevalence really wouldn’t add a huge amount of value. We have improvement programmes underway which are demonstrably reducing the risk of Lafora Disease in Mini Wires and cord1 PRA in all the miniature varieties. However, although we are doing research into IVDD, we have nothing in place which will reduce its prevalence.

So, for this year’s DachsLife 2015 survey we changed the focus from identifying the prevalence of health conditions to understanding lifestyle factors, particularly in relation to back disease (IVDD). We know that IVDD has a strongly inherited basis, but it is a complex condition where other factors are known to contribute to the risk of disc herniations. For example, in 2013, Rowena Packer and colleagues at the RVC reported some research that showed longer and lower Dachshunds were at a higher risk of herniation. She also showed that fatter dogs (with a high Body Condition Score) were also at a greater risk of herniations.

We were able to get responses for over 2000 Dachshunds which gave us a good sized data-set to analyse. My statistical skills are limited to what I can do in Excel which meant I was not able to do any of the multi-variate analysis Rowena had done in her study to understand the effects of a number of variables at the same time. Nevertheless, you can still get some interesting insights from such a large set of data with some relatively simple statistical techniques.

Surprises in the data!

The analysis you do depends on the question you want to answer; so for example we wanted to know in relation to IVDD:

  • Are spayed/neutered Dachshunds more or less likely to have back problems?
  • Does the age of spaying/neutering make any difference?
  • Can we reproduce the RVC findings about length and body condition?
  • What effect does exercise (type and amount) have, both as a puppy and as an adult?
  • What effect does diet have?
  • Are there any differences between dogs that are shown and those that are not?

I used one of the statistical techniques called the “Odds Ratio” which you might have seen in the VetCompass papers published by Dan O’Neill. Rowena also used it in her paper on back disease and it’s in the well-publicised 2013 Bellumori paper comparing the prevalence of inherited disease in mixed-bred vs. pure-bred dogs. It’s also widely used in reporting the results of human clinical trials, for example with new drugs. In humans, it might be used to compare the odds of someone dying when given a particular drug, compared with those given a placebo. We wanted to look at the odds of a dog having IVDD for different lifestyle factors:

Dogs aged >3 IVDD No IVDD
Neutered<1 114 205
Not Neutered 81 282
Odds ratio 1.936

In this example, the Odds Ratio of 1.9 shows that dogs over the age of 3 were nearly twice as likely to have suffered from IVDD if they had been neutered under the age of one than those who were entire. You also need to check that this is “statistically significant”, which it is in this case. (I won’t bore you / frighten you with how to do that!)

Our analysis showed:

  • The odds of a neutered Dachshund suffering IVDD over the age of 3 is nearly double that of an entire Dachshund.  Neutering under the age of 12 months has higher odds of IVDD than neutering over the age of 1.
  • None of our analyses showed a statistically significant difference in the Odds Ratios for overweight dogs being at a higher risk of IVDD.
  • We couldn’t reproduce the RVC relationship showing longer dogs had a higher prevalence of IVDD. However, our analysis suggests that more “rangy” dogs were more likely to suffer IVDD than “stocky” dogs.
  • Dogs over the age of 3 that were highly or moderately active were half as likely to have suffered an IVDD incident than dogs described as mildly or not at all active.
  • Dachshunds over the age of 3 that were allowed to go up/down a flight of stairs every day had a lower probability of IVDD than those not allowed to use stairs.
  • Dogs over the age of 3 that did not participate in KC Open or Championship shows were 3.8 times more likely to have suffered an IVDD incident.
  • Dachshunds living with more than 1 other Dachshund or living with other (non-Dachshund) dogs had a lower prevalence of IVDD than Dachshunds living on their own.

Start with “Why?”

Some of these results are surprising, certainly when compared with conventional wisdom like “don’t allow your Dachshund to go up and down stairs”. The question you have to ask is “why might there be this association?

The neutering result is particularly interesting given the veterinary profession’s apparent obsession with early neutering. We could possibly build a case to explain this along the lines of the impact of neutering on growth plates and normal development. Interestingly, the findings of a 2013 paper showed neutered Golden Retrievers were more likely to suffer from Hip Dysplasia. Our data also showed that spayed bitches were no less likely to suffer from Mammary Tumours than entire ones; another finding that tends to contradict conventional wisdom.

Why might dogs that are shown be less likely to suffer IVDD? Are they kept in leaner, fitter condition than those that aren’t shown? Why might dogs that live with more than one other dog be less likely to suffer IVDD? Do they get more exercise from playing with each other?

As with many surveys, our results raise more questions. You also have to recognise that “association” is not “causation”. However, the analysis does provide some fascinating insights which we will be able to use to provide advice on some of the lifestyle factors that may help reduce the risks of IVDD. Rowena Packer has also kindly offered to do some more fancy statistical analysis on our data so I’m looking forward to seeing what emerges from that.

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