Popular Sires and (ir)responsible Stud Dog owners

There has been much discussion about whether or not the Breed Council’s Health Plan should include guideline limits for the number of litters any individual Stud Dog should sire. The draft plan, issued for consultation proposes a limit of 20 litters over the lifetime of a Stud Dog. It also suggests limiting the number of litters to be sired per year.

The rationale behind this is to avoid the potential health issues that are known to arise from so-called Popular Sires and to enable the breed to work towards lower overall Breed Average Coefficients of Inbreeding.

The Breed Council had been tracking and reporting the number of litters sired by stud dogs and, in general, the data showed in the Miniature varieties there were a large number of dogs being used (350 MS, 200 ML, 100 MS), but a few dogs were siring between 12 and 20 litters in a year. In the Standards, where registrations are much lower, unsurprisingly, far fewer stud dogs were being used (typically 30-40 different dogs over an 18 month period).

The impact of a single Stud Dog on genetic diversity and potential health risks is therefore much greater in the Standard varieties than the Minis.

What the Breed Council’s analysis didn’t show was the Coefficients of Inbreeding of the litters produced by the most popular stud dogs.

I thought it would be interesting to do some analysis of this and, with the Kennel Club’s Mate Select and the newly launched MyKC web service, it’s quite easy to do, albeit rather time-consuming.

I don’t claim this to be a statistically robust analysis; it is simply illustrative of the issues that a Stud Dog owner needs to be aware of.

Example 1:

One Stud Dog had sired an average of 7 litters per year and had sired 15% of all the puppies registered in his breed. Of the litters I looked at, 85% had a Coefficient of Inbreeding greater than the current Breed Average COI value. In other words, more than 8 out of 10 of the litters had an adverse effect on the breed’s genetic diversity.

Further analysis showed that a third of his litters had COI values that were more than double the current breed average COI and one was as high as 25%. You’ll probably recall that the KC has banned matings such as Father-Daughter and Mother-Son which would result in COI values of 25% (probably higher). You’ll probably also know that high COI values increase the probability of two harmful genes combining to result in a health issue.

Example 2:

A second Stud Dog I looked at had sired an average of 17 litters per year which equated to 2% of all the puppies registered in his breed. In this case, a third of the litters had a COI value of more than the breed’s average and only one in 15 had a COI of more than double the breed average. So, in this case, you could argue that by mating so many “pet bitches”, this particular stud dog had contributed to reducing the Breed Average COI. Actually, the most interesting calculation in this case is the amount of income the Stud Dog owner has received from all the stud fees.

Example 3:

The third and final Stud Dog I looked at was an import who sired an average of 5 litters per year, amounting to about 8% of the puppies registered in the breed. Only 4% of his litters had a COI greater than the Breed Average; 15% had a COI of 2% and the rest were complete out-crosses (COI = 0%). In this case, the Stud Dog will have contributed to a reduction in the breed’s Average COI and added to its genetic diversity. Of course, there is a risk with imports that we introduce new, deleterious genes into the gene pool, but on balance, the increase in genetic diversity for the breed overall probably outweighs this risk unless the imported dog falls into the trap of being a Popular Sire. This again highlights the responsibilities of the Stud Dog owner to protect the future health of the breed.

I started this piece by talking about the Breed Council’s Health Plan and its guidance on the use of Stud Dogs. I admit I’ve only looked at three dogs, but each of these illustrates the heavy responsibility that lies with owners of Stud Dogs. They have the potential to act in the best interests of their breed, but how many are simply “taking a stud fee”?

Do let me know what you think.  What could we do to ensure we don’t run into problems that some other breeds have suffered?

Read more about Popular Sires.

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