Is One Same Parent Inbreeding?

We sold a male choc lab to my husbands sister from a litter two years ago. We now have another litter and she wishes to get one of the females to breed with the male we gave her. They are brother and sister but from two different litters. This is still inbreeding as I see it. I contacted the akc and they said they will register inbred pups and recommended I ask our vet. I asked them and they said they do not recommend this. I am looking for a second opinion in writing as it is my husband's sister and I want a strong case as to why I will check the limited registration on the papers of the pup. Please respond with the possible outcome of breeding a sister to a brother from two different litters with the same mother. (Cynthia Riser - Michigan)

It has been known to perform this kind of breeding exercise in order to 'fix' characteristics in a line. For example, if the bitch has particular qualities that the breeder wants to remain in the breeding line, then mating two siblings who each have the characteristic would help retain that trait for future breeding. However, and this is a big however, this breeding phenomenon also has inherent risks. With all inbreeding there is an increased risk of unexpected traits and problems. This is because hidden recessive traits can be brought to the surface when two closely-related animals breed.

What your sister-in-law proposes is not the same as breeding two siblings but it is very similar and could potentially have the same devastating effects. Now I'm sure that many readers will testify that they have never encountered problems, but the potential is what I think you are worried about.