Since Multi-Drug Resistance (MDR1) Gene Defect does not affect the health of the dog is it OK to breed a carrier to another carrier as long as the resulting puppies are tested for the defect (and the puppy buyers informed) ?

If you breed carrier to carrier, then about half of the pups, statistically, are going to be affected.     I can't see any justification for breeding practices which would perpetuate the problem.

Personally, if in a breed with limited numbers, I would breed Carrier to Non-Carrier, this would ensure no pups would be affected and also in the long term, move towards breeding out the gene for affected without limiting the gene pool unnecessarily.  If a breed with very high numbers, as in some breeds, I would only breed Non Affecteds.

Just my humble opinion ;)

It's a tough one because the MDR1 defect doesn't affect dogs normally but may if they are ill and the vets are not completely up to speed with which drugs to use and not use. Also a worry for me is eating horse poo outside, most dogs do it and who knows if that horse was recently wormed with an ivermectin based wormer. Also if you are deliberately breeding affected dogs who is to say where their offspring end up and if all owners are aware of the issue - a pup gets diarrhoea and the owner gives it immodium?

So, while it may not be the worst thing a dog can have there is now a very simple dna test that will help to eradicate this MDR1 defect, why not use it :-)

Because of the limited genepool of silkens in most countries (bar USA), carriers are being used in the breeding programme, with the intention to eventually breed the problem out, but not a carrier to a carrier.

For anyone reading this with a collie or any breed that may have the defective gene the dna test is a simple cheek swab that you can send off yourself to Laboklin so no excuse not to test :-)

It's going to be a long road to breed this out while maintaining quality and breed type.  There are far more serious defects (and temperament!) to be considered when choosing the right mate.
In the meantime, whilst breeders are trying to improve their lines, Vets shouldn't be giving any of the herding breeds these drugs.  There are usually acceptable and effective alternatives. To me it's the drugs that are wrong!

Thanks for your replies. As I expected there is not a right or wrong answer.

Dill your numbers are slightly wrong, but your argument is sound. A carrier to carrier mating would give probabilities of

25% affected
50% carrier
25% clear

However as WestCoast says there are worse conditions than MDR. So with that in mind if it is simply a case of avoiding the wrong drugs and horse poo (good point chaunsong) is this a condition that can be lived with and in the interests of not narrowing the gene pool too much should carrier to carrier matings be considered ?

I absolutely agree that there are far more serious problems, but as this is so easy to identify I think it should be considered :-)  And of course it's not just herding breeds, you would never think looking at a longhaired whippet or a silken windhound that they could carry the gene, same with a lot of crossbreeds and mongrels of unknown heritage. Several of the drugs that MDR1 affected dogs are sensitive to are well known, effective and reasonably priced drugs that vets like so saying they shouldn't be used it not really a viable solution.

In breeds like say border collies any breeder could probably find a wide choice of suitable mates for their bitch, so choosing one that compliments her traits and pedigree and is also MDR1 clear shouldn't be a problem.

>in the interests of not narrowing the gene pool too much should carrier to carrier matings be considered?

Depends entirely on the breed and available dogs imo :-)

In breeds like say border collies any breeder could probably find a wide choice of suitable mates for their bitch, so choosing one that compliments her traits and pedigree and is also MDR1 clear shouldn't be a problem.

You may say that Rough Collies are not a numerically small breed but I couldn't find a clear stud dog with the temperament, breed and health qualities that I was looking for but then I'm very fussy!

Accepting that all drugs have undesirable side effects, shouldn't we be asking the drug companies to produce drugs that don't have such serious harmful effects to so many dogs instead of trying to change our dogs to suit commercial pockets?

I am inclined to agree with West Coast.  I think the natural inclination will be not to use carrier to carrier wherever possible therefore the mere fact testing is possible should reduce affected dogs in time.
What does the breed club say?

>Dill your numbers are slightly wrong, but your argument is sound. A carrier to carrier mating would give probabilities of

>25% affected
>50% carrier
>25% clear

You are correct of course Mark, I should have checked my post before clicking.

I suppose the real question regarding this, is whether the breeders have any intention of trying to eliminate the problem through breeding?  
If so, then not breeding from Affecteds is the way to go.  

If not, I'm not sure there is any point of using the DNA tests, but then that also brings in to question the ethics of breeding from dogs with a known and avoidable problem and then selling the progeny.

DO NOT USE in dogs with MDR1 defect.

An affected dog (-/-) carries two MDR1 gene mutations, having received one from each of its parents. It will also  pass on a mutant MDR1 gene to its offspring.

MDR1-affected dogs are likely to experience drug toxicity following normal doses of the drugs listed here:

Anti-Parasitic drugs:

Ivermectine substances: Diapec®, Ecomectin®, Equimax®,Eqvalan®, Ivomec®, Noromectin®, Paramectin®, Qualimec®, Sumex® & Virbamec®

Doramectine substances: Dectomax®

Moxidectine substances: Cydectin® & Equest®

Loperamide substances (anti-diarrhoea): Immodium®

Metronidazole (Flagyl ® - general antibiotic

http://www.karibunicollies.com/home/mdr1
very useful information.

there are plenty of clears in Roughs to pick from .

I have no experience of MDR1 but I do know that the Animal Health Trust advised SBT breeders not to breed carrier to carrier for L2, which is of course a much more serious condition.
As others have said, I can't see the reason to breed carrier to carrier if the breed is numerically strong.

> If you breed carrier to carrier, then about half of the pups, statistically, are going to be affected. 

For clarification If it's a recessive condition just 1 in 4 are likely to be affected, half carriers, and 1 in 4 unaffected.

As this is not a specific health condition, just an intolerance to chemicals it's a tricky one.

Personally my view would be in a numerically strong breed why breed Carrier to Carrier if breed improvement is the aim, as only 1/4 will be clear of the gene, as opposed to at least half if using a carrier to clear.  Surely the latter course would help you get clear of the gene more effectively, without losing the positive traits of the carrier animals.

there are plenty of clears in Roughs to pick from
After 30 years breeding my interpretation of the breed standard, I'm still looking for the breed type, temperament or health standards that I want. :)  I certainly this into account but I am far more concerned about health issues that are more detrimental to an active healthy dog life.

I was around when a well established kennel lost more than half of her dogs due to her Vet using Ivomectin on all of her dogs before the situation was known.  But now there is no excuse for the number of Vets who are ignorant to drug sensitivity.  All my puppy owners are given printed up to date information about this with their puppies.

Obviously I found my ideals as I posted a site , also even going back years -Sandiacre ,Corydon, Ingledene, and I will be watching the new Canadian import  with interest....

I'm still looking. :)

I presume breeders looking for tested stud dogs have had their bitches tested for breed specific problems

Personally think all has to be taken into account... breed type, health results and also the bitch you are putting said stud too.... too much is emphasis is being put on MDR1... hip scoring is just as important,, as are all health tests..

> Personally think all has to be taken into account...

Exactly.  Every breed club should have a health committee who keep themselves fully informed of all the issues and potential issues affecting their breed and sit regularly to reassess and advise their members.

Personally think all has to be taken into account

Absolutely. :)  For me health testing, temperament and breed type are all part of the equation.  Unfortunately I want it all, which is why it's so difficult and after 30 years it's becoming harder and not easier............

What of course can really complicate matters is where more than one, sometimes half a dozen or more problems for which DNA tests are available is taken into account.

There may be few dogs that are clear of everything, so decisions need to be made re priorities, and those problems that affect a dogs normal quality of life are the highest!

possibly this is where breed type comes in... as personally I would rather use something of breed type that is perhaps not clear than use something that is obviously not of breed type and clear.. there are lots of things in the decison of which stud... To use an import just because its MDR1 clear when in USA there are other diseases and problems we do not have here like Bloat, Grey Collie Syndrome... lots to think about..

I this only collie related?

> I this only collie related?

This is the list of affected breeds from the Laboklin site, of course any cross, lurcher, mongrel of unknown heritage may also carry the defective gene.

Australian Shepherd , Border collie, English shepherd , Longhaired Whippet , McNab Shepherd (McNab Border Collie) , Old English Sheepdog , Shetland Sheepdog (Sheltie) , Silken Windhound, Rough Collie , Smooth Collie , German Shepherd, Bobtail, American White Shepherd.

I think to use the Canadian import rough collie gave a COI of 0.0%. All health tests done on dog and bitches . It was seen as a way forward .I certainly will be watching the pups

There may be few dogs that are clear of everything, so decisions need to be made re priorities, and those problems that affect a dogs normal quality of life are the highest!

as personally I would rather use something of breed type that is perhaps not clear than use something that is obviously not of breed type and clear..

Well said both. :)
There are so many factors to be taken into consideration.  Of course health testing is a priority but when there are many things to consider, debilitating issues rather than Vets using the wrong drugs or drug companies producing products that are not suitable will be higher on my list.

I also know of many long established breeders who are SO obsessed with health testing that by keeping and breeding from only clear dogs, now have a kennel full of dogs who bearly resemble the breed and only get placed at shows under their thankfully very clique who agree with their thinking.

Others are importing  clear dogs who may fit the breed standard in their country but IMO do not fit our UK standard in anyway.  I've also known of dogs imported for the best reasons but were later found to have untypical temperaments. 

NOTHING is so simple as just mating clear to clear (you may sort out one problem but find that you've amplified another!) and to think it is, is just like the Emporer's New Clothes and shows blinkered and narrow minded thinking. :(

Responsible breeders have enough to be thinking about without drug companies marketing drugs that are unsuitable for so many dogs and Vets not reading the packet inserts and using them on the wrong dogs.