Dog breeding is a very complicated process and should be taken up by professionals only. Dog breeding is about improving the breed and not about bringing a litter into this world. There are simply too many dogs dying in shelter homes mainly due to careless and thoughtless breeding. You should not breed your dog simply because you want puppies.
A professional and responsible dog breeder knows the pros and cons of various kinds of breeding. The decision that he takes will keep in mind the welfare of the dogs and the future puppies.
Various Types Of Breeding
Inbreeding: refers to the mating of closely related animals, like mother/son, father/daughter, sibling/sibling, and half sibling/half sibling. Inbreeding produces uniform and predictable offspring. Dog breeders do it to eliminate unwanted traits and to double up good genes. The other benefit is that hidden genes show up and they can then be removed. Inbreeding also has negative consequences for the breed. In the long run, the breed becomes genetically impoverished. Faults and weaknesses add up in a breed. It also leads to reproductive failures and loss of vigor.
Line-Breeding: I refers to mating of less closely related dogs. It produces predictable offspring and slows genetic impoverishment. It does not halt genetic impoverishment, but only slows it down.
Out-Crossing: refers to the mating of unrelated dogs within the same breed. In dog breeding it would mean that a common ancestor is not present behind either parent within a four or five-generation pedigree.
Out-Crossing: The breeding is done to bring in new qualities and to reintroduce lost qualities. It improves the immune system, vigor and reproductive capacity. The offspring are not predictable and it might bring in some unwanted quality.
Hybridization: refers to the mating of unrelated breeds. It may result in a totally new breed. It brings in new qualities and reintroduces lost ones. The offspring are considered impure for many generations. It might result in a new breed. On the negative side it might bring in qualities that are totally undesirable.
Inbreeding Eugenics
Too much inbreeding will ultimately lead to a breed that has a pure immune system. Inbreeding has resulted in problems in several breeds. For example, breeders carried out extensive inbreeding in Pugs to have a flatter face and a rounder head. This resulted in more c-sections being done. Due to inbreeding some breeds cannot give birth without human assistance.
Issues like genetics, line-breeding, cross-breeding, etc can be too complicated for a layperson. That is why it is advised that dog breeding should be left to professionals, who know the breed in and out. It takes many years to completely understand all aspects of dog breeding and even then one can never be to sure.