Interesting article on blue - blue breeding

I came across this article whilst looking for information on the prevalence of CDA in blue staffys. It's a bit of an essay but makes for some interesting reading if you can spare 10 minutes.

"Discussion about blues and the numbers being registered is seldom off the various social internet sites. Like everyone else, I deprecate the actions of those who breed blue Staffords (or French Bulldogs etc.) purely for money without due regard for the quality of their dogs, whether in relation to the Standard or to their health. The topic has become so emotive that clear thinking has become very cloudy in many instances. As one who simply wants the scientific truth in this matter (and all other such topics) I have sought the comments of the academic experts, as well as trying to get reliable information on any associated problems.

I will assume that readers will understand the workings of the ‘D’ (dilution) gene and its recessive ‘d’, of which there are at least two alleles or variants, one of which is more common in dogs in general and is the only one to be found in some breeds; it is not known if both are present in Staffords or not. It is ‘d’ when homozygous, i.e. a dog carries two copies, one from each of its parents, that produces ‘blue’ by causing the eumelanin (black) pigment in hairs to clump rather than be evenly distributed throughout.

Firstly a question – ‘Is there any difference, in respect to ‘d’(assuming it is the more common allele involved), between a blue dog produced by two brindles that carry it or one which is the result of blue to blue matings over several generations?’ The answer is simply ‘No’! If you tested each dog, either by DNA sequencing  or by the DNA tests for ‘d’ offered by some companies, you would get exactly the same result, which in turn means that the expression of ‘d’ in both would also be the same. In the course of correspondence regarding blue to blue matings, Prof Schmutz of Saskatchewan University, who is regarded as the queen of colour genetics, simply stated that you can’t get “more homozygous” by the process and did not see why it would matter, thus supporting what has been pointed out above. Prof Tosso Leeb of Bern University, whom I also consulted, responded in a similar vein seeing ‘no rational reason for a ban on blue x blue matings’

Some confusion may have arisen by using the term ‘dilution’ for the gene which in scientific literature is now referred to as the MLPH gene in accordance with its function at the molecular level. It was the American geneticist, Clarence Little, the father of coat colour genetics, who coined ‘D for dilution’ in the 1940s on account of its recessive ‘d’ ‘diluting’ black to blue (actually a slate grey) as he put it and nothing more. Some however may have the impression that when you mate two blues or dilutes together you are then ‘diluting’ further and further with each generation, which is simply untrue. Once the initial ‘dilution’ has occurred to produce the blue dog which is homozygous ‘d/d’, then that is the dilution process complete!

There are of course anecdotal reports of blue to blue matings producing coat and other problems, plus comments that many blues are different from other colours in build and appearance. Should this be considered so, it is almost certainly a question of ‘bad’ breeding rather than ‘blue’ breeding. If you breed for one particular aspect, in this case a colour, without regard for the whole dog (or other animal) then you are asking for trouble. This is something that has been seen in other species, for example in cattle where breeding for milk production solely has had serious adverse effects on cows’ health.

The big problem is a virtual total lack of data, i.e. peer-reviewed papers in scientific journals, and there would need to be several to ensure that any finding was corroborated. I am aware of some papers of a histological or molecular nature but none on the incidence of coat colour-related conditions in dogs in general or in specific breeds. (If anyone comes across any, please let me know.) Hearsay and anecdote have been the basis for so many opinions when firm data is essential.  In fact a vet I was talking to very recently at a seminar highlighted this lack of facts and figures.

In Staffords we must be very aware that perceived coat problems may not be confined to blues. I know we are again forced to rely on anecdotal opinion, but if one goes back thirty years or so you may have heard of certain stud dogs being associated with progeny with poor coats and I do recall seeing brindle dogs, supposedly from a certain popular line, with ‘spectacles’ of hair loss round their eyes. Some may recall I asked vets from a large canine charity (Health Bulletin 14), plus others along the way, for their thoughts and clearly the body of opinion was that blues were no more affected with skin and coat conditions than other colours, in fact some vets consider that whites may be at greater risk.

Currently the greatest hope of getting meaningful data is the VetCompass project which receives information, including coat colour as well as the usual parameters, from many veterinary practices on all ‘patients’ being seen. I have spoken to Dr Dan O’Neill the veterinary epidemiologist in charge about our concerns. At the moment no data has been extracted in relation to coat colour but, having asked the right questions, it is on the ‘to do’ list. However, even if health conditions were found to be more prevalent in blues (or any other colour), thus showing a correlation, that would not be the end of the matter. Correlation does not equal causation! Further studies would be necessary see if the colour genes were actually involved and to rule out co-incidental findings such as inadvertently selecting genes for other conditions.

To appreciate why great care is needed with ‘correlation’ we only have to look at the hereditary cataract cases that emerged in the late ‘nineties’. There was a correlation with the red breeding, with a few saying to keep away from the ‘reds’, but no one with the least understanding ever claimed it had anything to do with their coat colour or the genes that produced it. It was just chance that it came to the fore in reds.

The one condition that is associated with blue dogs is colour dilution alopecia (CDA) where the blue hairs become fragile and break off. It can vary in severity and may lead to extensive bald areas where the skin may be affected by dryness and infection requiring long term topical treatment. White areas, if present, are not affected and in blue fawns CDA is likely to be much milder simply because of there being much more phaeomelanin (red) than eumelanin (black) in their hairs. However many blues (of many breeds where the genes are the same, as well as Staffords) have good, even excellent, coats with no problems so one cannot say that, although only blue hair is affected, the d/d genotype is specifically the cause. Expert opinion now considers that some other, as yet undescribed, genetic factors are involved; these will also be carried by non-blues but have no effect because of the different coat colours. There have been attempts to understand CDA but sadly very little progress has been made and there would seem to be no current research. Prof Leeb does have a call online for case reports plus specimens; I have no idea what the response has been but one suspects it has not been overwhelming.  This may simply reflect a low incidence of CDA but perhaps VetCompass will shed light in due course. In addition, only one of the vets surveyed from the large canine charity referred to above reported seeing a case of CDA. Furthermore if a blue dog does have hair loss, all other possible diagnoses, such as demodex, allergy, etc., must be eliminated before considering CDA and if there is reasonable recovery, CDA can almost certainly be excluded. In the course of discussions, it was suggested that if breeders of blues were concerned about the possibility of CDA or similar coat and skin problems, then they ought to ensure they used only dogs with visibly good coats. This of course is common sense and constitutes ‘good’ breeding.

Of course the absolute way to eliminate all risk of CDA would be to discourage or prohibit breeding for blues as the colour is essential for the expression of those genes that may be the real cause.  As far as we in UK are concerned, this would mean changing the Standard by deeming blue to be ‘highly undesirable’ along with liver and black and tan.. In fact some years ago I wrote an article to this effect pointing out the anomaly of permitting blue but not liver or black and tan, bearing in mind that black and tan is a perfectly normal coat colour and liver is produced by black eumelanin being replaced with the brown variety, without any hair abnormality, which the eumelanin clumping in blues undoubtedly is.

As many know, there was no mention of ‘blue’ in the original 1935 Standard, being only added in the 1948 review. There is no documented evidence of why this was done to my knowledge. It may be that blues pre-1948, were included with brindles and fawns but added after the genetics had been described by Little as mentioned above. Thus if a change in the Standard to discouraging blues, because of perceived health issues, were to be proposed, the inevitable question is why has it taken well over sixty years to be raised? And more importantly, where is the evidence, in the form of peer reviewed papers, which will withstand scientific scrutiny?

Even if the KC were persuaded to implement such a change, the greater threat of legal action is a possibility. A commercial breeder, all above board and licensed with the local council, might sue the KC (or other KC’s or similar bodies that have implanted colour breeding restrictions for registration) as their business might be adversely affected. Unless I am greatly mistaken (the legal experts will correct me I’m sure) the KC would back down rapidly as they would know that it was a lost cause."

I tried to post the link but as I have not yet been a member for 7 days I cannot but it is on the North West Staffordshire Bull Terrier Club under health bulletins, and is health bulletin 24.

Great article.

As stated within, there is very little peer-reviewed evidence to suggest that blue's have a higher incidence of skin problems, so many are reliant on personal experiences and anecdotal evidence. I've only recently begun learning about genetics (I'm studying A level biology) so this is something of interest to me, but having also worked in kennels for many years previously, blues (and whites and fawns, I will add) do appear to have more severe skin problems. Whether this is due to bad breeding or genetics is not clear. Though it also states here that CDA is a blue issue...

Ultimately, I do think that the issue with blues is the popularity of the colour and the standard of breeders that are producing the puppies. I very rarely meet a blue that is to standard, many look like crossbreeds.

I'm a scientist myself. Currently undertaking a PhD in drug design and metabolism, but throughout my undergraduate degree I done various modules on genetics so I have a strong understanding of the genetic science behind it.

I agree with your view that the issues encountered within the blue population are down to poor breeding for colour and money rather than issues with the MLPH gene itself.

Also from what I can gather, CDA can occur in any blue dog, regardless of whether it came from parents of two different coat colours or whether it came from parents with two blue coats.

Therefore my conclusions from this article are as follows. If someone has a blue dog of any breed then there is a chance that they can develop CDA, although it is an inherited disease, there seems to be a number of genes involved that are responsible for this disease coming to fruition, and it doesn't depend on the pairing of blue blue parents or mixed colour coats, the moment a dog has the heterozygous MLPH gene of 'dd' there is a chance of CDA, although it seems to be fairly uncommon.

Bad skin conditions appear to be a result of poor breeding rather than an association with a specific coat colour.

Therefore if you are in my position and your puppy comes from a family with two blue parents, if the parents seemed to be in good health, HC and L-2HGA clear, with a good coat then you will more than likely have a good healthy puppy. BUT you have to be prepared and accept that fact that down the line there could be a chance that a puppy could develop CDA.

It would be good if in the future a test was developed for all breeds of blue where they could test for CDA in an attempt to remove it from all breeds of dog. Maybe one day...

Wow, that sounds really interesting! I'm really enjoying the science based subjects, my degree starts in September in Occupational Therapy.

So, sorry if this is wrong, just trying to understand ore clearly - whilst all dogs with a blue coat can potentially develop CDA (though which combination of genes involved in this occurring are not clear), but if both parents hold the heterozygous dilute gene there would be a 50% chance of the pup being Dd (heterozygous) as opposed to 25% of being either homozygous (DD) or recessive (dd)? So if a blue bred with a black it would not make a difference because the MLPH gene is already dilute?

This issue has been long debated on this forum, more so when there were different admins/regular members who were interested in breeding. I don't have a lot of interest/input in breeding personally (I don't have the time with rescue/study!) but I do think this discussion is important to further prevent issues.

Another concern of mine in regards to gaining the blue colour is that people are so willing to inbreed their dogs to guarantee the colour that they want.. I think that inbreeding is a practice which we can all agree should not be happening to the level that it is.

A very interesting read and from what I gather there is no real evidence that a Blue/Blue breeding in itself will/won't cause an issue but could increase the risk ?

The best way to understand dominant and recessive allelles is through diagrams:





So what these two images show is that two carriers have a 1 in 4 chance of producing a dilute, whereas a blue and a black breeding produces a 2 in 4 chance of producing a dilute. And of course two blues breeding creates a 4 in 4 chance of producing dilutes i.e. 100%. What the article states is that once a blue dog is blue, you can't get more dilute, once they're dilute, that's it, they're homozygous.

Any blue dog can get CDA, so all that this means that if 2 blue dogs breed, then there are more blue dogs within the litter, so naturally the odds of one of those dogs in the litter developing CDA increases ONLY if the parents carry the genes responsible for CDA. Blue dogs and black dogs can carry this gene, so it doesn't matter if it's blue blue or black blue, the blue puppy from the litter can still develop CDA.

As for other skin conditions, that appears to be purely down to breeding itself. If you have a stud that has skin problems and he so happens to be blue and sires a number of litters, then he passes of his genes to his offspring resulting in them having bad skin.

Ah ok, so that rules out the myth that a blue/black combination is more safe than a blue/blue depending on whether the parents have the gene in the first place.

I guess the only way to eradicate the problem is to have some test for the condition so as to breed it out.

From my understanding yes, the only reason that those with a black coat cannot get CDA is because it is specific to the dd genotype, but they can still carry it. If we call the mutated gene responsible for CDA d1, then the image below shows that two parents with black coats can produce a dilute puppy with CDA.

Now that's got my internet, is it then suggested that Blue/Blue is at increased risk if one or more has the gene and also black/black breeding ?

My son is at Uni studying human bioscience so this will be an interesting conversation to have with him