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Merle Color In Cocker Spaniels - Analyses Goal #2

Analyses

Goal #2: Provide scientific evidence the Merle color can produce significant health issues.

Findings

  • There are a number of articles that describe significant health issues that may arise when breeding Merle dogs
  • The AKC-Canine Health Foundation (AKC-CHF) lists Merle as a disease for which there is a genetic test. The AKC-CHF has therefore concluded that Merle is detrimental to the breeds
  • Based on the PNAS paper from 2006, the mutation for Merle is a disruption of the of pigmentation gene SILV. If this mutation is present, it can result in numerous health issues since the disruption occurs early in the development cycle and those cells then form many different body tissues which then can lead to a wide range of auditory and eye abnormalities. This can occur in both homozygous and heterozygous dogs. The research identified both the mutation and the ‘cryptic’ (phantom) mutation.
    • A referenced study with Dachshunds, studied the hearing capacity for Merle phenotype homozygous and heterozygous dogs and found that over 50% of homozygous dogs and just over 30% heterozygous dogs have auditory problems ranging from mild to severe deafness. All control dogs having no mutation for Merle had normal hearing
    • One can conclude that breeding a Merle to a non-merle can result in health problems nearly as frequent as breeding Merle to Merle (30% vs., 50%)
    • In other cited studies, the homozygous genotype can be sub-lethal and is associated with multiple abnormalities of the skeletal, cardiac, and reproductive systems
  • Common problems cited in an article in the AKC Gazette, dated August 2010 include cyclic neutrorpenia, white spotting and deafness, deafness and blindness, and color dilution alopecia.
    • Cyclic neutorpenia occurs in collies which can result in loss of pigment and internal, life threatening infections
    • Significant linkage has been identified that produces blindness and deafness in both heterozygous and homozygous dogs.
    • The homozygous of double merles have a much higher incidence of eye and ear abnormalities
  • A study lead by Dr. George Strain included several breeds of dogs of which 40 were homozygous (double Merle) and 113 dogs were heterozygous. The results were conclusive.
    • 29 of the 40 were Catahoula, a breed with no white markings – only 2 were deaf in both ears and 1 was deaf in 1 ear
    • Of the remaining 40, 11 dogs included 5 Aussies, 3 Collies, 1 Sheltie, 1 Corgi, and 1 Great Dane and 4 were deaf in both ears and 3 in one ear
    • Only 1 of the 113 dogs was deaf – leading to the conclusion that heterozygous dogs are not prone to deafness

Conclusion

  • Breeding Merle dogs introduces risk that offspring may have significant health issues including but not limited to blindness, deafness and color dilution alopecia and other problems leading to death
  • This is especially true for homozygous offspring resulting from breeding Merle to Merle
  • For significant health reasons, breeding Merle to Merle is strongly discouraged
  • Breeding Merle to non-merle has similar health risks although the incidence is reduced
  • The existence of the “cryptic” mutation introduces significant risk because it is not evident visually. Therefore, if you do NOT know the Merle status of a male you are planning on breeding to, a responsible breeder should perform a DNA test for the Merle mutation as a cryptic Merle may not show Merle phenotype but can produce Merle offspring

ASC Flushing Spaniel Show The 2016 ASC Annual National Specialty Show

will be held July, 2016

at Purina Farms in Gray Summit, MO

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