Here is a great topic most do not truley understand. They think linebreeding is a bad thing. Here is the best I have heard it explained out of Gonnie Shaffer and Robert Gavels book Neapolitan Mastiff.
" Inbreeding.... Inbreeding consists of breedings that are very close, i.e.,Father to daughter, mother to son, full siblings, half brothers to half sisters. These types of breedings will result in the very best offspring or the very worst possible genetic combinations. The worst will come if you do not know all of the shortcomings of the dogs that you are dealing with. You should never inbreed when dogs have the same serious fault. If you ascribe to these types of breedings, you must be mentally ready to cull any abnormalities. Inbreeding should only be done by the knowledgeable breeder.
Linebreeding...... Linebreeding is the breeding of relatives,i.e., uncle to niece, aunt to nephew, first cousins, grandfather to granddaughter, and grand mother to grand son. Linebreeding is also known as breeding within a family or bloodine. In this type of breeding, you do not gather all of the negative genes immediately; you are bringing out the best without too drastically doubling up on problems. We prefer this type of breeding, and you should use linebreeding for three to four generations before using a modified outcross.
Outcrossing..... Outcrossing consists of breeding two dogs that are totally genetically unrelated. Technically, in order to truly outcross, you need to choose a totally different breed, because all dogs in a given breed came from the same small foundation group. Looking at a pedigree, there may be no relatives in the first, second, or third generation,but looking back further in the pedigree you will find common ancestors. Most dog breeders therefore refer to an outcross as a mating with no common ancestors in the first five generations.
When linebreeding for many generations, you may have a problem or deficiency that you want to correct. An outcross breeding is then used, and a dog is selected that is dominant in that trait and produces it in his or her offspring. The resultant offspring is then bred back into your line.
Many breeders of Neapolitan Mastiffs continually out cross their dogs in order to get very big dogs (Hybrid Vigor). There is nothing wrong with that, but you can never fix a type that is distinctive to your dogs alone. If you continue to outcross, you end up with a hodgepodge of different looks along with different genotypes. Most of the desirable genes in the Neapolitan Mastiff are in the recessive state, and it may take several generations to lock one specific trait into your dogs. Like inbreeding, outcrossing should never be done by the novice breeder.
One reason why there are many different head styles is the failure of the breeders to employ inbreeding or linebreeding consistently, thereby fixing head type. Many of the breeders here in the United States breed indiscriminately (outcrossing continually,no rhyme or reason to a breeding program),or breed to whomever is winning at the shows. Only a few breeders that employ linebreeding really know the power that this type of breeding can have for a breeding program. You must have short-term goals and long-term goals. Short-term goals focus on problems that can be corrected in a relatively short period of time. Long-term goals are ones that will take considerably more time. Also, keep in mind that if you have the same problems after five years and have not made any progress, you must reevaluate your breeding program."
