Selection by pedigrees alone, without consideration being given to the physical traits of the mating pair, is the chief danger in this system of breeding. The writer can state in the following few words the most important counsel to those who would attempt linebreeding: Physical compensation is the foundation rock upon which all enduring worth must be built. A linebred pedigree is valuable or dangerous in exact proportion as the individuals have been selected. Linebreeding does not replace selection but, on the contrary, demands the most discriminating choosing within the line. If the breeder selects by pedigree, and without consideration to physical compensation, undoubtedly dogs with notable faults will result, and thus linebreeding will ensure failure quicker and more certainly than will any other known system of breeding.
The word “confined” is used advisedly for, after linebreeding has been practiced for a few generations, the end result is the development of what is in effect a pure breed — a breed within a breed, so to speak. When that has occurred, any attempt to introduce “cold” blood (that of unrelated dogs of other strains) is likely to result in the penalties of hybridization. The departure from linebreeding is a kind of “crossing” in a small degree, for when the blood of line bred animals becomes intensified they assume all the attributes of a distinct strain, which in truth they are, and they will likely behave as such for a long time.
In saying that linebred dogs tend to become like pure breeds, or strains within their breeds, and that their progeny from a union with unrelated animals are like hybrids, I do not mean that such breedings should never be made, or that the results would be like breeding into an entirely different breed of dogs. While in some strains of animals linebreeding and inbreeding have been intensified to a point where a herd or flock would be practically a breed of their own, I do not personally know of such a family in any breed of dogs today. However, there have been strains developed in some breeds to a point where their blood has become so dominant that it will not yield for several generations to any noticeable blending when outcrossed, the characteristics of the inbred or linebred parent always showing up. This is, of course, to be expected.
Fortunately there are in almost all breeds of dogs a very few fanciers intent upon consistently producing dogs superior to the average of the breed. Many of these know that the quickest and most certain way to do this is by linebreeding.
Of course there is more.. But I'm assuming this will give enough to talk about for a while.