CDP Position on Merle and the Ethical Implications of Color in Selective Dog Breeding.

Circa 1582-1584 - "Danish Stover"

Human preferences for certain colors of dogs have historically played a significant role in the distortion of dog breeding priorities. Despite claims in the origin stories of many breeds about color being connected to function, in most cases, these claims are overstated and/or irrelevant in modern dogs. Color restrictions in breed standards have resulted in unnecessary reduction in genetic diversity in many breeds. Emphasis on appearance in general, beyond color, has contributed to narrowed gene pools, exaggerated phenotypes, and the normalization of traits that compromise welfare. In modern pet dog breeding, many breeders choose colors not based on historical breed standards, but on market demand for flashy markings or "rare" types. The color selection problem cuts both ways. Whether selecting for flashy colors to please paying customers, or selecting against out of standard colors in a pure bred program, breeders are making the the same mistake - treating superficial appearance as a marker of quality.

People enjoy how dogs look, and aesthetic response is a normal part of the human dog relationship. We don't need to be ashamed of or deny our desire to mold canine appearance. However, we do need to stop breeding dogs in ways that de-emphasize the welfare of either the individual dog, or the population of dogs overall. This is the focus of recent efforts by many, especially in the UK, to limit the breeding of extreme conformations. CDP supports these efforts. However, we question the inclusion of merle in lists of innately unhealthy traits.

Coat color and pattern on their own should be neutral in breeding choices. They should neither drive selection nor trigger categorical exclusion. Treating color as either a virtue or a vice elevates aesthetics above function and reproduces the same structural error that has historically undermined dog welfare. What matters is how any trait functions, how it is managed, and what welfare consequences it produces in real dogs.

Merle is a dominant coat pattern caused by a mutation affecting pigment development It is not a modern invention or a designer novelty. Merle is a long-established coat pattern in collie-type and shepherding dogs, documented in working sheepdogs by the 19th century and likely present earlier in landrace herding populations, well before modern breed standardization. Within these populations, dogs were selected primarily for working ability. Merle survived the selection pressures of earlier times and persisted in the canine population until today. Its pleasing appearance to many people has likely played a role in its persistence, and, currently, it is definitely being selected for by some breeders for aesthetic reasons- as are many other traits including short legs, brachycephaly, and extremes of size.

Merle has the potential to be harmful to dogs. Dogs with a single copy of merle carry a very small but measurable increase in risk of hearing impairment, comparable to, and in some cases lower than, risks associated with other widely accepted phenotypes, including extreme white or piebald patterning . Irresponsibly made merle pairings, usually involving two merle dogs bred together, can produce a high incidence of congenital impairment, including deafness and vision abnormalities, which can be devastating to the individual dog..

Merle is notable for the severity of the defects it can cause and because it is often visible, but it is not truly unique. There are many other testable genetic mutations that create harm if not managed competently. Exercise induced collapse, caused by a recessive mutation in DNM1, can result in collapse and death during exertion in affected dogs, while single copy carriers are not expected to show disease. Degenerative myelopathy, associated with a recessive SOD1 mutation is another example. Progressive retinal atrophy affected dogs predictably develop progressive blindness, while single copy carriers remain clinically normal. Dogs with these mutations are routinely bred safely by using genetic testing to avoid breeding two carriers together.

Banning a visible trait such as merle does not eliminate the need for breeders to be competent. Modern dog populations carry numerous deleterious mutations, most of them invisible, many of them serious, and all of them requiring management. Any framework that prohibits merle while permitting the unmanaged breeding of other known inherited risks is internally inconsistent and does not reduce harm. Ethical breeding cannot be achieved through aesthetic prohibition. It requires genetic and phenotype testing, transparency, informed mate selection, and acceptance that stewardship of dogs includes stewardship of imperfect genomes.

The genetics of merle have been extensively studied and documented among breeders. There is a wealth of information widely available and testing for the length of the SINE insertion that creates merle is accessible. All breeders should be knowledgeable about genetics and common risks in dogs, including merle, and dogs should be tested as needed to avoid known risks.

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Which breeds have merle naturally?

"All breeds which have Merle have it naturally, a pair of dogs have bred and as one parent was Merle, some of the offspring are also Merle. Nothing non natural has happened, like artificially triggered mutations or gene transplanting. The real question is which dog breeds with closed stud books have had Merle traditionally from the start of the stud book, and which have gotten it later through non recorded crossbreeding." The First Merle Dog By:  Liisa Sarakontu

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Modern companion dogs do not exist primarily as genetically isolated breeds. While breeds remain culturally and historically meaningful, canine genetics do not care about AKC registration. Traits, mutations, and disease risks are widely shared across the entire canine species. Modern breeds themselves are largely a social construct, not a biological one. Breed club and TikTok warriors' claims about whether a trait, like merle, "occurs naturally" in a breed are based in a purebred culture and ideology that CDP does not ascribe to.

This perspective underlies CDP’s support for purpose bred mixed dogs and open breeding strategies. Mixing breeds does not introduce fundamentally new ethical problems. The reality is that all breeding decisions already involve managing complicated trade offs, risks, and responsibilities.

CDPs position is therefore as follows:

Historical claims about the morality of merle based on breed are ethically baseless. Merle is a "naturally occurring" trait of canines. Humans, even the keepers of the breeds in which it was historically present, do not own merle. Modern breeders, as stewards of the current canine population, should treat merle like any other existing potentially harmful mutation. Merle status should not exclude a dog from breeding when that dog is otherwise the best available candidate based on temperament, health, structure, and functional suitability for the breeding goal, but the goal should be to reduce or maintain the traits presence over time, not expand it. Merle should not be over represented within any breeding population, nor promoted as a distinguishing or desirable feature. Its presence does not confer value, and its absence does not confer virtue. All merle breeding must be accompanied by diligent appropriate genetic testing, clear disclosure, and pairing decisions that reliably prevent harmful outcomes.

To review CDPs complete ethical and registry standards visit our site .

References

1. Strain GM, Clark LA, Wahl JM, Turner AE, Murphy KE. Prevalence of deafness in dogs heterozygous or homozygous for the merle allele. J Vet Intern Med. 2009 Mar-Apr;23(2):282-6. doi: 10.1111/j.1939-1676.2008.0257.x. Epub 2009 Feb 3. PMID: 19192156.

2. Patterson EE, Minor KM, Tchernatynskaia AV, Taylor SM, Shelton GD, Ekenstedt KJ, Mickelson JR. A canine DNM1 mutation is highly associated with the syndrome of exercise-induced collapse. Nat Genet. 2008 Oct;40(10):1235-9. doi: 10.1038/ng.224. Epub 2008 Sep 21. PMID: 18806795.

3. Coates, J. R., and Wininger, F. A. (2010). Canine degenerative myelopathy. Veterinary Clinics of North America Small Animal Practice, 40(5), 929 to 950.

4. Mellersh, C. S., et al. (2006). Identification of a mutation in the canine PRCD gene associated with progressive retinal atrophy. Genomics, 88(3), 321 to 329.

5. Langevin, Mary: The Story of Merle - Merle - SINE Insertion from Mc - Mh