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Puppies from 2 Merles


TravelerBlue
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First, I know that a merle should never ever be bred with another merle.

 

I'm in contact with someone, however, whose 2 merles had an accidental breeding. My questions are these:

1. If the puppies seem to see and hear well at 8 weeks, does that mean they escaped any consequences, or might deficiencies from the breeding appear later?

2. Do puppies who suffer from a merle x merle breeding necessarily have the mostly white coat? The puppies in this litter look like typical merles, with only a normal amount of white, does that mean they escaped consequences?

(I don't think the owner has done any vision or hearing testing, I think she's just going on the fact that they seem to hear and see just fine.)

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Since merle is a dominant gene, out of a litter of four pups from a merle/merle breeding, (on average) you could expect one "traditionally-marked" (black/white, red/white, black tri, or red tri) pup; two merle pups (each with one merle gene); and one double-merle pup (with two merle genes). That's on average so you *could* have all normal pups in a litter from a merle breeding, whether the pups were traditional colors or merle.

 

Pups that have vision or hearing issues due to being double-merle would have those problems from the get-go as they seem to be related to the absence of pigment in the essential tissue areas (for instance, in the ear canal for hearing problems). This is not something that would occur over time but which would be present from the start.

 

While it's typical for double-merle animals to have a lot of white, I don't know if that's true in every case. I do know that I've seen pups from a white-factor to white-factor breeding where there was unilateral deafness in two pups, and it did not occur (at least in one of the pups) on only the white side of the head. In other words, one pup was deaf in one ear that appeared normally-colored but apparently was missing pigment within the ear, where you could not see.

 

Pups (and dogs) can be very good at compensating and, in the case of unilateral issues, it can be hard for someone to realize that a pup has hearing or vision problems (versus being totally deaf or blind). Our Megan, who has early onset deafness, began to lose her hearing at age 5 and was clinically deaf by age 7, and yet was so quick to respond to visual cues and cues from the other dogs, that it was really hard to realize that she was actually not hearing.

 

I would think the best thing to do would be to have a trained veterinary professional examine the pups to look for visible signs of improper eye development and vision problems, and to have a BAER test done to determine the presence (or absence) of deafness and/or hearing issues. People can do certain informal "tests" at home that might indicate a problem but it would take a professional to properly assess the presence or absence or degree of impairment.

 

Oftentimes, vision and hearing issues that might not be readily seen in a pup will become manifested when the pup is in a new home and undergoing training, and the new owner might feel the pup is stubborn, obstinate, rather stupid, etc., when in reality the pup is simply not able to obtain and process visual and auditory cues properly.

 

Best wishes to these pups - I hope they are all fine and healthy.

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If both parents are heterozygous merles, statistically they should produce 50% heterozygous merles, 25% solid, and 25% homozygous, or double, merles.

 

But real life doesn't always follow statistical probability. A typical merle to merle breeding would be expected to produce 50% merle puppies. But some planned merle to merle breedings produce no merles at all. And others will produce more than 50% merles. Theoretically the puppies could all be merles. It's possible the person was incredibly lucky and none of the pups ended up getting 2 copies of the merle allele.

 

AFAIK, all double merle puppies are overly marked white, but I don't know that for a fact.

 

ETA: I was typing at the same time Sue was. I agree that the pups should be be checked by a vet or vets who can do the specific testing necessary.

 

I know someone who produced a mostly white (non-merle) pup who was bilaterally deaf. It took him quite a while to figure it out because the puppy responded on the basis of what is litter mates were doing.

 

Unilateral deafness would be even harder to determine without proper testing.

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Double merle pups can rarely appear almost like normal merles- it's uncommon, sure, but it does apparently happen. The dog hasn't always read the rules: see the dachshund with microopthalmia in this post. I am not saying that this is the case in that litter, just that it is possible.

 

Heterozygous merles are also prone to hearing and vision abnormalities, it's a lot less common than in double merle dogs but still higher than non-merle dogs.

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Heterozygous merles are also prone to hearing and vision abnormalities, it's a lot less common than in double merle dogs but still higher than non-merle dogs.

 

I'm not sure about vision abnormalities (is there evidence of this? The citation deals only with deafness), but while the risk for hearing loss is somewhat higher in heterzygous merles, it's not as high as it is in blue eyed solid colored dogs, and the risk isn't as great as it often seem from the warnings.

 

The paper cited is worth reading in its entirety. Across the breeds in this study, deafness, the total percentage of deaf heterozygous merle dogs -- unilateral and bilateral combined -- is 3.5% (0.9% bilateral and 2.7% unilateral).

 

25% of homozygous merles were deaf (10% unilateral, 15% bilateral).

 

Not at all trying to be snarky, but wanting to put it in perspective. :)

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No, you're grand GentleLake! I had intended to convey that meaning from the quoted sentence (hence 'a lot less common') but that apparently wasn't how it came across. Thank you for clarifying!

 

 

I cannot find my hard drive with my random stock of dog studies (and all my work-work for many years, but that's another story) so I cannot verify that I haven't just misremembered* or made it up about vision being affected.

 

* Which is entirely possible even though I am subjectively SURE I didn't. But then isn't everyone 'sure' who misremembers like that?

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Agree with the folks who say BAER test. I'd probably have a vet (if not an ophthalmologist) check the eyes just to be safe. I brought home a unilaterally deaf pup and knew within half an hour that he was a uni. He had a mostly white sister who was bilaterally deaf. Once the uni adjusted to the environment, an owner might not have realized that he was deaf in one ear. They probably would have chalked up the occasional "not listening" to, well, not listening.

 

In litters where there is a lot of white on any one pup, all puppies in the litter can be affected with deafness. Any time there's a risk, the smart (and kind to potential puppy buyers) thing to do is BAER test.

 

If this person ended up without any double merles, I hope she counts her blessings and becomes extra vigilant over preventing such a breeding in the future. It sounds as if she got lucky this time, but may not if that particular roll of the dice ever happens again. The bad results of a merle x merle breeding can be heartbreaking, so please encourage her to be extra careful about preventing a recurrence going forward.

 

P.S. Unilaterally deaf dogs can seem to hear just fine, especially when part of a litter. I had another situation where someone offered me a pup, thought he heard just fine, but when I asked for a BAER test (because of a lot of white) discovered that he, too, was a uni. The pup I described earlier was not known to be deaf, nor was his sister, until they were taken out of their normal environment, at which time it became fairly obvious (at least with the bilaterally deaf pup). Others observed the uni and disagreed with me and made excuses for the things he did, but I knew which ear and the BAER test confirmed it. For a pet, that wouldn't have been a big deal (and he's in a wonderful pet home now), but for a working dog, the ability to hear and triangulate sound at long distances is critical, so I couldn't keep him. I adored him, so it was really sad to have to give him up. He ended up in a good place, but I can envision him having gone to a farm and then being punished for not responding appropriately because no one knew his hearing wasn't normal...

 

J.

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So ... I think I'm concluding this: if a pup has markings very typical of normal blue merles or blue merle tri's, it's very highly unlikely that it would have the deafness associated with double merles. Yes?

 

As pointed out above, if the pups are heterozygous, you have about a 3.5% chance of deafness. But you may or may not be able to tell if any pup is deaf, especially unilaterally deaf, just from observing it in the litter.

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There's a place a couple hours from the breeder's home that does BAER testing. Gonna see about testing the pup there before bringing him home. Breeder agrees to take him back if there are issues.

But he does have heavy coloring on face and body, which pushes heavily (I think) against him being double.

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