I am very sure that there is no black piggy in play in the narrow genetic pool that the pups are displaying and that must go back a few more generations before they were dumped.
Both Millyn and Baeddan have unusually small eyes; they are technically half-siblings as they share the same mother (Modron).
The four pups are showing a very limited palette of coat colours and markings; they are also all halfway breed mixes between aby and smooth. In the first one or two generations babies tend to look like one parent or grandparent in terms of breed appearance.
A good example of a first generation mixed breed baby is my Tegan, who has come out fully on her peru inheritance in terms of breed, coat colouring and markings and not one bit on the short-hair smooth side of her lilac coated and ruby-eyed dad. Although she is much looking more like her aunt Ffwlbri than her buff mother Tesni!
True halfway mixes - like all babies - tend to appear usually much more in later generations with both parents having an increasingly mixed inheritance themselves and the gene mix that is passed on is therefore more and more hodge podge. You would by then also see a wider variation in the new offspring with a wider gene pool in their ancestry; they wouldn't look as similar as my four do.
My Rainbow Ark Triplets (Morwenna, Myfina and Myfina) were even a bit further down the line in the breed mixing process in terms of each girl being a different combination of two of three breeds in play with Myfina displaying markers of all three - which is rare. But they also clearly illustrate the greater variation you get with a less limited gene pool.
PS: It could have been a rat or an unrelated piggy. Poor sod if the second was true!
