THE DILUTE GENE IN LABRADOR RETRIEVERS – HEALTH PROBLEMS AND BEHAVIORAL PROBLEMS

Silver_Labrador_Retriever

by Jack Vanderwyk

The American Kennel Club (AKC) (and all other reputable kennel clubs around the world) recognizes three coat colors in the Labrador: black, yellow and chocolate. These colors are inherited based on genes at two loci: B and E. In recent years, other colors have become more prominent in the breed. Breeders refer to these colors as ‘silver’, ‘charcoal’ and ‘champagne’. In order to obtain these new colors, a recessive D locus dilution factor (d) must be introduced into the population. According to literature, the dilution factor was not originally a part of the Labrador Retriever breed, and therefore, controversy surrounds the topic.
Information known about the dilution factor’s lack of presence in the Labrador suggests that it was introduced into the breed in the United States, at some point in time, probably in the late 1940s, early 1950s, by crossbreeding. Research has shown that some dogs with coat color dilution are prone to hair loss and reoccurring skin problems. These conditions should be selected against by eliminating dilution factors within the Labrador population.

The Labrador Retriever breed should be consistent with its breed standard, and dilute colored dogs incorrectly represent the purebred breed.
The Labrador Retriever breed, as it was developed and registered in the United Kingdom, never (until 2006) carried the dilution factor. A survey in the United Kingdom, Europe, Canada and the United States shows that no reputable Labrador breeder has ever had a puppy carrying the dilution factor, so it is hard to explain the direct cause of a mutation in the breed. There is no other explanation than that crossbreeding occurred with a breed carrying dilution, probably the Weimaraner, and they passed the d allele down to offspring.

There are many breeders in the United States who specialize in breeding diluted “Labradors”. Diluted dogs typically have a metallic-looking sheen to the hair. A typical Labrador with a black phenotype can have the genotype: BBEE, BBEe, BbEE or BbEe. A Labrador with a chocolate phenotype will have either the bbEE or the bbEe genotype. A dog displaying a yellow coat must have the homozygous recessive genotype at the E locus, and therefore can be BBee, Bbee or bbee. It is possible for these genotypes to be diluted if the dog carries two copies of the recessive dilute gene, dd. Dogs that carry at least one D will not have a diluted coat. If a dog carries the Dd genotype at the D locus, one copy of the dilute gene is present. If bred to a bitch carrying a dilute gene (Dd or dd), diluted offspring could be produced.

Health problems and misconstruing of breed standards due to dilution

Various expressions of the dilution gene have been noted. Some dogs with dilute color display minimal or no health problems; other dogs experience hair loss and skin problems. Color dilution alopecia (CDA) and black hair follicular dysplasia (BHFD) can accompany coat color dilution. These diseases cause recurrent skin inflammation and drying, bacterial infections of hair follicles and severe hair loss. Late 2013 a 12-week-old female silver Labrador Retriever was submitted to the Comparative Ocular Pathology Laboratory of Wisconsin, and was diagnosed with Malignant Uveal Schwannoma. Scientists believe that the dilute color mutation may contribute to the cause.
Other disorders that could travel with the dilution gene are heritable Weimeraner genetic issues such as trembling disorders, autoimmune related vaccination sensitivity and intolerance, Von Willebrands Disease, hyperuricosuria causing painful bladder and kidney disease, and behavioral problems that are more common in the Weimaraner, such as separation anxiety, and dominant, protective, territorial temperament. Minimizing occurrence of these conditions would mean minimization of the dilute mutation. Selection against dilution is important in breeds that display health issues associated with the mutation. It is also important to minimize the dilution mutation in breeds that do not have a standard written which include these colors. The Labrador Retriever is currently one of these breeds. Dilute colored Labrador retrievers are a disqualification according to breed standards. Those dogs carrying the dilute gene should not be registered as purebred Labrador Retrievers.

The Labrador Retriever Club Inc. is the AKC Parent Club of the Labrador Retriever. On May 12, 2014, the LRC published the following message on their website: “Very exciting news – the OFA has agreed to maintain a database of Labradors who have been permanently identified (microchip or tattoo ) and have been tested for the d gene. Dogs having the genotype dd will be listed as affected, Dd as carriers of the dilute gene and DD as clear of the dilute gene. This is great news for us.”
Note: The Orthopedic Foundations for Animals (OFA) only registers hereditary diseases (or the lack of those) in their databases. So it’s not a simple matter of “a different colour”.

Implications

Although findings of these various studies do not definitively explain the cause of dilution in dog coat colors, they help us to understand the correlation between dilution and the MLPH gene. Knowledge that the MLPH gene mutation is responsible for dilution has allowed DNA testing companies to begin testing for the mutant dd allele. These tests can help identify carriers of the d gene, and therefore, can help to eliminate it from populations, such as the Labrador retriever, in which it is undesirable. Responsible breeders should take the time, and spend the money, to have their breeding stock genetically tested at the D locus. Labradors displaying dilution, ‘silver’, ‘champagne’ or ‘charcoal’, coloration (dd) should not be used for breeding. Ideally, only Labradors with genotype DD at the dilution locus should be used for breeding.

Throughout the years, Labrador breeders have worked diligently to eliminate undesired traits and illnesses in the breed. A complete elimination of coat color dilution in the Labrador retriever would take a very long time, through DNA testing and breeding stock selection. Kennel clubs and breed clubs are expected to respect the breed standard and the closed character of the studbooks. No respect of the breed standard and the closed character of the studbooks is shown by the common practice of registering “silver” as chocolate, “charcoal” as black, and “champagne” as yellow. Labrador retriever breeders are equally expected to follow the breed standard as currently written when selecting parents for future litters.

The situation in Europe

The AKC registration of “silver”, “charcoal” and “champagne” dogs as chocolate, black or yellow Labrador Retrievers, without any restrictions, has resulted in the disturbing fact that in 2011 the first American dilutes were imported into the United Kingdom, and that these dilutes were registered by The Kennel Club, also without any restrictions. As a result, hundreds of dilutes were born in the United Kingdom, and most of them were registered by the K.C. as completely normal black, chocolate or yellow Labrador Retrievers. The Kennel Club told the Labrador parent club that “DNA-tests” proved that these dogs were purebred Labrador Retrievers, and that there was nothing they could do about it.

The Kennel Club did not mention when these “tests” took place. However, it’s a matter of fact that these tests are extremely unreliable. Yes, the tests could show that the parents and grandparents of a certain dog are Labrador Retrievers, but does that make a dog a purebred Labrador? Even the most modern and sophisticated tests are not able to say something about anything that happened more than three generations ago, while many dilutes have a history that goes back to the 1970s, or even to the 1950s.
So, instead of using an extremely unreliable test to “prove” that a Labrador is purebred, the K.C.’s should use a test that is reliable: any dog carrying the d-gene can not be a purebred Labrador Retriever and should be excluded from the registry.

References

– Coode, C. 1993. Colour Inheritance. Labrador Retrievers Today. Howell Book House, New York. 28-32.
– Drögemüller, C., U. Philipp, B. Haase, A.R. Günzel-Apel, and T. Leeb. 2007. A noncoding melanophilin gene (MLPH) SNP at the splice donor of exon 1 represents a candidate causal mutation for coat color dilution in dogs. Journal of Heredity, 98 (5), 468-473.
– Duke, F.D., L.B. Teixeira, L.E. Galle, N. Green, R.R. Dubielzig. Malignant Uveal Schwannoma With Peripheral Nerve Extension in a 12-Week-Old Color-Dilute Labrador Retriever. Vet Pathol, Feb 10, 2014.
– Kurtz, K. 2013. Genetic aspects and controversies of coat color inheritance in the Labrador retriever. Animal Science 314, Michigan State University.
– Philipp, U., H. Hamann, L. Mecklenburg, S. Nishino, E. Mignot, A.R. Günzel- Apel, et al. 2005. Polymorphisms within the canine MLPH gene are associated with dilute coat color in dogs. BMC Genetics, 6, 34.
– Philipp, U., P. Quignon, A. Scott, C. André, M. Breen, and T. Leeb. 2005. Chromosomal assignment of the canine melanophilin gene (MLPH): a candidate gene for coat color dilution in Pinschers. Journal of Heredity, 96 (7), 774-776.
– Schmutz, S.M., and T.G. Berryere. 2007. Genes affecting coat colour and pattern in domestic dogs: a review. Animal Genetics, 38, 539–549.
– Templeton, J., Stewart, A., and Fletcher, W. 1977. Coat Colour Genetics in the Labrador Retriever. The Journal of Heredity 68: 134-136
– Vanderwyk, Jack 2012. Analysis of the ‘silver’Labrador population.
– Welle, M., U. Philipp, S. Rüfenacht, P. Roosje, M. Scharfenstein, E. Schütz, et al. 2009. MLPH genotype: melanin phenotype correlation in dilute dogs. Journal of Heredity, 100 (suppl 1), S75-S79.

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About Jack Vanderwyk

Hey! What am I like! :-)
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3 Responses to THE DILUTE GENE IN LABRADOR RETRIEVERS – HEALTH PROBLEMS AND BEHAVIORAL PROBLEMS

  1. judy says:

    This article is correct! I bought a silver labrador and it is horrible seeing her itch and dig her skin and hair off! If I could display a photo of her I would.

  2. EmilyS says:

    There was a similar controversy around merle American pit bull terriers. Merle is not a color that has historically been associated with that breed, and is not genetically possible. Merle APBTs are mixed breeds, probably created using the Catahoula Dog. The 2 registries for that breed, the UKC and the ADBA, have removed merle dogs. BTW, I’ve always thought the silver “Labs” that I see look like Weimeraner mixes, but the owners, and some serious Lab people have denied it.

  3. Kris Thompson says:

    I’ve owned three silver labs for over ten years. Being dog lovers we have stood by them thro so many skin conditions and now g:3 lymphedema in one. I can honestly say, controversy aside, I wouldn’t go down this sad road again. At 10 we are about to lose our first silver. She only has hair on her head(the two silvers are like that, we have a charcoal that is reasonably healthy). It’s a constant battle to keep her and one of her sisters healthy. I’ve spent thousands. Just be careful, I think as there are more generations and lines they may gain feasibility but I can only tell you my story.

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