I respectfully disagree that there is more than one source for the dilute situation we are experiencing today. The fact that there have been no “designer colors” of silver, charcoal, or champagne to appear in Great Britain until only a few years ago ( and those from dogs imported from the USA who trace back to the suspected line) indicates that the dilute influence on color is not native to the Labrador.
Whether or not the appearance of the Weimeraner is purely coincidental is speculative since we had no DNA testing or micro chipping and breeding records were, and still are, the responsibility of the individual breeder. Could there have been other breeds who contributed the dilute factor? Yes, but the fact that we had no silvers being produced anywhere in the world until after the development of the “pointing labs” here in the USA, tilts the scales, in my opinion.
Please remember, if Weimeraners and Labradors were crossed, you would not see any unusual colors being produced until after the first generation of offspring since the mode of inheritance of the dilute factor is a simple recessive. So each F1, or first generation mixed offspring, would simply be carriers. Only when a dilute carrier would be bred to another dilute carrier would there be any chance at all for the production of a dilute affected offspring. It is the same mode of inheritance for any other simple recessive condition such as PRA or EIC.
On a side note, the coincidental jump in the AKC heights for Labradors after the advent of the “pointing lab” being developed may be just that, but interesting that only Canada followed suit in the difference in heights from what was previously the standard followed in the country of origin, Great Britain, and in every other country across the globe.
Consider this timeline:
1916 – Great Britain – original standard for Labrador Retrievers written – in correlated writings, heights were suggested to be 21 1/2″ – 22″ for bitches, 22″ – 22 1/2″ for dogs
1917 – USA – AKC standard for Labrador Retrievers virtually identical to GB standard
1928 – 23 Labradors registered with AKC
1929 – 1st pair of Weimeraners imported to USA
1931 – 40 Labradors registered with the AKC
1933 – 1st AKC Champion Labrador Retriever
1943 – AKC recognizes Weimeraners
1946 – there were 1736 Labradors registered with the AKC (Prior to the WWII time period, when dogs were not being shipped in or out of Great Britain because of the advent of the war, there was a great deal of importation of British Labradors into the USA. Most, if not all of the Labradors registered with the AKC were imported from, or bred from, recently imported British Labradors
1950s – the first “pointing” Labradors were developed
1956 – AKC standard standard revised.
22.5 – 24.5 for dogs and 21.5 to 23.5 for bitches.
1985 – AKC registers first “Silver”, Spook Culo born 2/2/1985. However, there may have been “silvers” registered as chocolates for several generations before Spook Culo.
1987 – AKC limits Labrador registration to three recognized colors
2006 – 1st “silvers” born in the UK on June 8, 2006. Registered as “Non Recognized
ShadowGlen Labradors, reg.