Effective Population Size

Effective population size is not related to the breed population or to a set of named dogs. It is really a measure of genetic diversity within a breed. Imagine an area of Africa that has a total lion population of, say, 120, 60 females and 60 males. They live in prides where only the leading male will be allowed to breed. Each pride has 15 females so each of those will be mated to this single lion.


This means that although there are 60 males only four of them will be bred from, so the effective population size will be 64, not 120. . Added to this the genetic diversity of the population will become less and less as the prides go through one 'bottleneck sire' after another. There are many reasons why some Beardies are never bred from. They may be sold as pets and neutered, their owners may not wish to breed or they may never get the chance to mate a bitch. The more dogs that sire multiple litters the less bitches there will be for others to mate and the lower the effective population size


Most male lions will never get the chance to reproduce

This has been happening in Beardies since the earliest days. One well known sire of the 60s has more than 26,000 descendants at four generations, goodness knows how many today as I can't work that out! Just imagine how many times he appears in individual pedigrees, it is not unusual to find him 20 or more times. This increases the risk of an individual puppy inheriting two identical genes from him, those genes might be beneficial but they are just as likely to be detrimental, harmless on their own but harmful when 'doubled' to make the puppy homozygous. And he is only one of many, many bottleneck sires in the breed. The lower the EPS the greater the risk. An EPS of less than 50 is considered to be unsustainable and at high risk of detrimental effects of inbreeding as well as being at risk of known and unknown genetic disorders. The EPS of the Beardie is less than 24. No one is to blame for this situation, we all did what we thought was right at the time. I am as guilty as anyone. Jendie, Ch Gillaber Drummond, sired 28 litters. This is less than half the number sired by some of his contemporaries but it was still far too many. But he was a great dog who sired great puppies, six of them won CCs at Crufts and five won groups at Ch Shows. I didn't think allowing him to be used so much was wrong, I thought he was producing super Beardies. He was...but I had not learned that in the long run so many litters by a single dog would be wrong for the breed. I've learned and I hope others have and that we can work together to remedy the situation. Having tantrums will not help anyone. We MUST put differences aside and move forward.

My dog is a wonderful Best In Show winning paragon of beauty. He does not carry any 'bad' genes and I'll sue anyone who says he does!


Some owners become irate when it is suggested that their Tom, Dick or Harry carries undesirable or harmful genes. They are convinced their beloved Tom, Dick or Harry is clear of any faults, genetic or phenotypical and they are ready to do battle with anyone who suggest otherwise. Sadly their view is simply rubbish. The average dog will have around 400 potentially damaging variant genes and a couple of disease causing mutations. We may not, at this stage in our knowledge, be able to identify all of these or even determine their effects, but there is no doubt they are there. Whilst the genes are heterozygous, that is matched by a ‘healthy’ gene they will cause no damage but once they are homozygous, matched by the same deleterious gene, they will cause problems.

Beardies have an effective breed population size of less than 24, a fact that puts us firmly in the ‘serious risk’ category. We need to breed for diversity and in my opinion this should have higher priority than breeding to win in the show ring.

What should the effective population size be?

An effective population size of more than 100 is considered to be sustainable

An effective population size of less than 100 is at risk

An effective population size of 50 is considered to be at serious risk

THE BEARDED COLLIE HAS AN EFFECTIVE POPULATION SIZE of 23.9, based on a Kennel Club analysis of inbreeding between 1980 and 2014


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