130 replies to this topic

[terrecar]

Penny, are you claiming there are health issues with Mm?
According to Prevalence of Deafness in Dogs Heterozygous or Homozygous for the Merle Allele the rates of deafness in Mm are 2.7% uni and 0.9% bi. Are these really that different than the rates of deafness in Border Collies or other breeds?

Prevalence of Unilateral and Bilateral Deafness in Border Collies and Association with Phenotype
Hereditary Deafness in Dogs and Cats: Causes, Prevalence, and Current Research

Hi Mark. I really shouldn't be spending time here, as I have work up to my eyeballs. But having checked in...I've seen studies that suggest Mm isn't a problem as well, but then there is this study that indicates otherwise (looking at the percentages in the Reetz study): http://www.pnas.org/...103/5/1376.full (Retrotransposon Insertion in SILV Is Responsible for Merle Patterning of the Domestic Dog) with an excerpt below:

Dogs having Mm and MM genotypes typically have blue eyes and often exhibit a wide range of auditory and ophthalmologic abnormalities (3). Reetz et al. (4) studied the auditory capacity of Dachshunds and found that 54.6% of MM and 36.8% of Mm dogs had auditory dysfunction, ranging from mild to severe deafness. All control dogs (mm) in the study had normal hearing. Klinckmann et al. (5, 6) conducted ophthalmologic studies with three groups of Dachshunds (MM, Mm, and mm) and found that merles and double merles had significantly greater frequencies of ocular abnormalities, including increased intraocular pressure and ametropic eyes. Microphthalmia and colobomas are well described in merle and double merle Dachshunds and Australian Shepherds (3, 7, 8). In all breeds, the double merle genotype can be sublethal and is associated with multiple abnormalities of the skeletal, cardiac, and reproductive systems (3, 9, 10). For these reasons, merle-to-merle breedings are strongly discouraged (9).

• Leigh Anne Clark*,†,
• Jacquelyn M. Wahl*,†,
• Christine A. Rees‡, and
• Keith E. Murphy*,§

ETA: Sorry Shore's Dog. I only just now saw that you had posted the exact same study and (not surprisingly) the same paragraph.

[terrecar]

Double merle breeding.

Actually...ya' got me. I had never seen it in the show world until now. Just another reason to add to my many reasons to be soured on the AKC breed ring. I saw from the GSD judging that most still have over-angulated wobbly rears, as well.

[MrSnappy]

We have (had) a homozygous merle pup in my shelter until yesterday. She's a sable merle. She has a completely detached retina in the one eye, with a few small colobomas throughout the iris. She has an almost detached retina in the other, with several large colobomas throughout. She's got nystagmus in the one eye that is normally shaped; the other is microthalmic. She's functionally blind. It's pathetic.

We don't know what she is, breed wise. She's one of our famous "spotty rez dogs" who seem to get pumped out with some regularity in the area she's from. We assume she's a homozygous merle because the litters of some spotty / some not we get in are always healthy and "normal" across the board for sight and hearing.





My experience with the merle litters has been that the merle-to-solid breedings, producing both merle and other patterned pups are generally fine. The merle-to-merle breeders generally produce some problem dogs being deaf/blind or both. One litter produced all merle puppies, who were all fine for sight and hearing - but two did die in the shelter prior to our taking them, so that may have been related to the merle/merle, but we'll never know because they died.

I think it's very sad. A merle to solid (etc) breeding will produce 25% or more merles with the rest being solid (etc). A merle to merle breeding will produce all merles, but a percentage I can't remember off hand will generally be problematic for sight/hearing. The importance placed on a "perfect" merle is largely what drives breeders to do the double merle breedings - the number of merles will be higher (100%) so the odds of getting a "good" one are higher, but the odds of producing defective pups are also a lot higher. Breeders will argue that they are doing it carefully and conscientiously, but I have trouble with equating "careful and conscientious" with a deliberate production of potentially deaf and/or blind pups.

I know one breeder who bred a red dog to a blue merle because they thought they'd get red merles. Le sigh.

RDM

[Gloria Atwater]

But Gloria, Lassie is not "correct." OMG, one of her ears tips more than the other! Her coat is certainly insufficiently thick and fluffy. And most importantly, her head is not shaped like a long thin cucumber.

Okay, you made me laugh. Thanks for a spot of levity in all this.

~ Gloria

[Mark Billadeau]

Hi Mark. I really shouldn't be spending time here, as I have work up to my eyeballs. But having checked in...I've seen studies that suggest Mm isn't a problem as well, but then there is this study that indicates otherwise (looking at the percentages in the Reetz study): http://www.pnas.org/...103/5/1376.full (Retrotransposon Insertion in SILV Is Responsible for Merle Patterning of the Domestic Dog) with an excerpt below:

The problem with the data in the quoted introduction is it comes from epidemiological studies which do not prove causation, only correlation; these studies did not distinguish between Mm and MM.

It you read all the way to the end of the linked PNAS article on the identification of the merle gene you find this which seems to be at odds with the quote from the introduction which implies Mm carries increased health risks.

A genetic test for the merle locus can help responsible breeders of merle dogs prevent undesirable double merle progeny by allowing them to (i) distinguish merle from nonmerle in light-colored dogs that show little contrast between areas of dilution and full pigmentation, (ii) classify harlequin Great Danes as single or double merle, and (iii) identify cryptic merles.

Taken in total it seems to me science has not decided if being Mm is unhealthy.



I concede that breeding to produce MM (which is clearly linked to health issues) was inappropriate. My philosophical question was about once you have a MM dog (which could be produced by merle x cryptic merle) is it any different than breeding a go normal dog.



For those of you who don't know, "go normal" is a term used to describe a dog affected with CEA but has little to no loss of vision. Many of you are assuming that every breeder is using the CEA DNA test prior to breeding; reality does not support this assumption.

[Mark Billadeau]

This has been an interesting discussion on people's philosophical stand and people's understanding of the state of the science on the merle gene. I certainly don't have all the answers and these exercises help me probe what I know and don't, differentiate it from what I think I know, and how this impacts my stand on subjects.
Thank you all.

[PennyT]

Penny,
I was wondering the same thing. She was active trialing when I was just starting out. I wonder if it really is her?

J.

Someone in Georgia should know. Trig was a good dog as I recall.

[terrecar]

The problem with the data in the quoted introduction is it comes from epidemiological studies which do not prove causation, only correlation; these studies did not distinguish between Mm and MM.

It you read all the way to the end of the linked PNAS article on the identification of the merle gene you find this which seems to be at odds with the quote from the introduction which implies Mm carries increased health risks.

Actually, that's why I specifically mentioned the Reetz study. That particular study did distinguish between Mm and MM, and in fact found the percentages of Dachshunds affected as follows:

Reetz et al. (4) studied the auditory capacity of Dachshunds and found that 54.6% of MM and 36.8% of Mm dogs had auditory dysfunction, ranging from mild to severe deafness. All control dogs (mm) in the study had normal hearing. (Clark, Wahl, Reest, and Murphy)

Having been forced to read through all the way through to the end, due to a summary I had undertaken for a course, I did read the last paragraph and found it to ignore the data on the Mm dogs as well. So, I agree with your statement that:

"Taken in total it seems to me science has not decided if being Mm is unhealthy."

I think that sums it up nicely.

[Mark Billadeau]

Actually, that's why I specifically mentioned the Reetz study. That particular study did distinguish between Mm and MM.....

How did the authors in 1977 determine the genotype of these dogs when the gene wasn't identified until 2005? Are the phenotypes in this breed 100% indicative of the Mm and MM genotypes? Is it possible that the differences between dappled and double dappled Dachshunds are just as easy to visually distinguished between as some white and excessive white in Border Collies (see BC hearing study link)?

[terrecar]

How did the authors in 1977 determine the genotype of these dogs when the gene wasn't identified until 2005? Are the phenotypes in this breed 100% indicative of the Mm and MM genotypes? Is it possible that the differences between dappled and double dappled Dachshunds are just as easy to visually distinguished between as some white and excessive white in Border Collies (see BC hearing study link)?

I am no scientist, so I can only speculate. I do know that MM Dachshunds present with white patches, while those that are Mm do not. Of course that is going by phenotype, so your point is well taken. However, it seems reasonable, given the way the merle presents in Dachshunds, that one would assume merle with no white as Mm and merle with white as MM. Of course, the fact that there are piebald Dachshunds might throw a wrench in that theory.

[ShoresDog]

How did the authors in 1977 determine the genotype of these dogs when the gene wasn't identified until 2005?

Perhaps they knew enough about the dogs' pedigrees and the phenotypes of their ancestors to be able to assign genotypes. After all, Mendel could do it with the smooth vs. wrinkled, green vs. yellow peas!

Let's stipulate that MM is horrible, and Mm is OK (even though I'm not convinced of the latter). I think it's agreed that the outcome is quite bad for MM dogs. I would turn the question about merle around and ask it the other way:


What good arguments are there for breeding to retain the merle trait?




That is a rescue dog that was available in Idaho a while back. I note that currently 4 of the 36 available dogs at Southern California Aussie Rescue's website are obvious double merles with vision and/or hearing loss. The 10-15% range for MM's in that rescue seems to be pretty constant, and there are rescues wholly devoted to double merle Aussies. Of course MM's should not be bred. But the reality is that in a breed that has a lot of merles, MM's will be bred, by accident, ignorance, or malevolent greed. Are we willing to see this happen to border collies?

[Mark Billadeau]

What good arguments are there for breeding to retain the merle trait?

Taking your argument to the ultimate outcome (based upon merle being dominate) you are proposing no merle should ever be bred.

[KnottyClarence]

I've been thinking of all those MM stud dogs, soon to be born to BYBs all over the country, to a life tied to a tree waiting for those money making merle bitches their owners will bring to them, now that Westminster has said it's okay to breed this way and merle is the hottest color in collies.

Our species has been saying that dogs are not "livestock" per se. Poor Avanalanche tests that conclusion for sure. He did, after all, do the job he was bred to do--provide his owners with stud fees from litters guaranteed to be "all merle breed ring champions." And the AKC, that primo promoter of household pets, is making sure that many many pets will be born with health problems with which the average owner cannot cope.

[ShoresDog]

Taking your argument to the ultimate outcome (based upon merle being dominate) you are proposing no merle should ever be bred.

Yes.

[Pam Wolf]

What good arguments are there for breeding to retain the merle trait?

I can't think of a single reason.

[SS Cressa]

keeping the merle gene...

If a dog is a good working dog... why would you discriminate based on color/markings alone? If its an all around healthy dog... would it matter its "color" skin?

[geonni banner]

If a dog is a good working dog... why would you discriminate based on color/markings alone? If its an all around healthy dog... would it matter its "color" skin?

There's a big difference between not breeding for the merle trait and discriminating against an individual dog because of its color. A good-working dog is never a bad color, but whether or not you want to use that dog for breeding - and how you use the dog for breeding is a different thing. I don't think most people here would discriminate against a merle dog in a litter because he was merle. But they might not choose him for breeding - and would certainly not choose him for breeding to another merle.

[ShoresDog]

If a dog is a good working dog... why would you discriminate based on color/markings alone?

Every time this issue has come up, it's argued in the hypothetical that one wouldn't want to discriminate against a merle who was a good working dog. But every time, no one comes up with a single merle dog who has superior and/or unique working qualities that it would be crucial for the border collie breed to retain and that would require breeding that merle. It's all along the lines of, "Seems like there was one sorta nice merle dog at Sheepdog Finals last year, but he didn't make the double-lift final." I have never heard anyone say that there are specific stock-working traits that would be lost to border collies if no merles were bred.

[Pam Wolf]

Every time this issue has come up, it's argued in the hypothetical that one wouldn't want to discriminate against a merle who was a good working dog. But every time, no one comes up with a single merle dog who has superior and/or unique working qualities that it would be crucial for the border collie breed to retain and that would require breeding that merle. It's all along the lines of, "Seems like there was one sorta nice merle dog at Sheepdog Finals last year, but he didn't make the double-lift final." I have never heard anyone say that there are specific stock-working traits that would be lost to border collies if no merles were bred.

There might be but I am not sure they would be desirable traits

[Mark Billadeau]

Yes.

If you hold this opinion based upon the epidemiological studies, then you should also hold the same opinion about white headed dogs and blue eyed dogs since these phenotypes are also associated with the same health concerns as merle. If you do not hold the same opinion about white head and blue eyed dogs, then you simply have a color bias against merle.