line breeding can be done sucessfully and would benifit the breeding program. It can cement good qualities such as good pigment, nice feet, nice head piece...ect...if you have recessive things..it will show up and you can not breed to it again...genetics are a sticky sittuation...but if done correctly it will benitit ..done poorly..it would bring horrable things.you have to knwo what you have.,.and know what your goals are..i personally dont call close inbreeding as line breeding such as father/daughter, mother/son, 1/2 sister/1/2 brother
I personally prefer to line breed. My line breedings produce more sound puppies and they set the things I want set in my program. One of my big things is temperament and my line bred litters have amazing temperament for the breed (Shelties). BUT I did a lot of research on the two dogs that I line breed on (meaning the dogs that I double up in the pedigree). I have seen both of them in person, laid my hands on them, still speak with their breeders on a very regular basis, spoke with other breeders breeding dogs from them, ect... I think that is important to do when you are breeding any pair of dogs - but with linebreeding you have to make sure that dogs that you double up genes from are examply specimens of the breed in health, conformation, and temperament, because you'll be seeing a lot of their traits popping up.
The closest line breed that I feel comfortable doing is 1/2 Aunt to 1/2 Nephew. They only have one common side of the gene pool. You also have to look at what the common dog would be to the resulting puppies - not so much to the parents. So in my case, the resulting puppies would have a common (or doubled up) grandfather and great grandfather. His genes actually probably work out to be as influential as the parents genes.
What a lot of folks don't understand is that while Out crossing doesn't necessarily double up on recessive faults as often it is like a surprise package. You don't really know what recessives you are dealing with either. Out crossing can produce just as problematic litters as Inbreeding can. The key to any breeding is to make sure that you know the dogs and their history - regardless of whether you plan to line breed. If you get a litter that produces a problem puppy, don't breed the two dogs together again. Breeding is a lot of common sense and a lot of homework if done correctly.
If any of yall know much about horse breeding, yall would really see the pros & cons of line breeding in general. I don't know how often dog breeders inbreed, but it is very common to find a horse with the same ancestor 3, 4, or even 5 times on the same side of the pedigree, & also on the other side. In a horse I think it's easier to see the affect as opposed to dogs because a horse is used in so many ways that exhibit their traits & can live 25+ years. When you can have 6 generations standing in front of you it's easier to see what traits have been passed down.
And you also see alot of father/daughter & half-sibling matings, but only when the breeder is very knowlegeable about the horses - what traits they consistently pass on, & when the horses are near perfect & will complete each other. A lot of great horses have been made this way. Though after a mating of that closeness, they will normally outcross because the traits will have been set, as was the purpose of the mating.
On the other hand, since people have no real control over the outcome of the breeding, you might just end up with a sorry looking horse who's mean & conformationally deformed, not to mention the recessive genes that when doubled up WILL shock you with something you probably didn't know your horse carried. I would imagine the same is true for dogs or any other species.
But I think as long as you know what you're doing and have the experience needed, the pros outweigh the cons most of the time, though I don't suggest anyone breed immediate relatives.