Robert you post an interesting question and if I correctly understand you are raising this question:
[FONT=Times New Roman, serif]"What is the term if there is one for crossing back such a line every five to say eight years.????? Its a type of OUT CROSSING but it is the same gene pool that both breeders started 50 years earlier." I think to what you referred is "sustained in and in inbreeding".[/FONT]
[FONT=Times New Roman, serif]Interspersed with the above question, you discuss improving a strain of White Plymouth Rocks (WPR) using line breeding (modified inbreeding) and liberal inbreeding and things you touch upon in your message seem to indicate this method.[/FONT]
[FONT=Times New Roman, serif]I bring up two old timers from the past to answer this complex question - Harry Graves and Maurcie Delanao (arguably two of the greatest fathers of the breed). They employed similar methods to develop and maintain their strains of White Plymouth Rocks.[/FONT]
[FONT=Times New Roman, serif]Your "1000 mile distance" isn't what's important; rather isolating two distinct but genetically identical strains of WPR's is what you seek. Likewise, obtaining a 3rd strain completely unrelated is necessary as well.[/FONT]
[FONT=Times New Roman, serif]As I was starting a beginner's discussion under the SOP string regarding "inbreeding"; this form of inbreeding you are raising would be considered even beyond the scope advanced breeding. I know of only a handful of poultry-men who have ever pursued this method of two and three line inbreeding programs; as it requires extreme patience, diligence and fortitude to accomplish. I am also not sure you could find 3 genetically pure lines of White Plymouth Rocks today.[/FONT]
[FONT=Times New Roman, serif]I will clumsily attempt to explain this method as explained to me by Harry Graves over half a century ago, below as simply and briefly as I can:[/FONT]
[FONT=Times New Roman, serif]Grading-up (selective breeding) and in and in inbreeding takes a period of 5 to 15 years. Grading-back (out breeding) through in and inbreeding takes another 5 to 9 years.[/FONT]
[FONT=Times New Roman, serif]The first planned mating of the first cross of WPR hens with WPR cockerels, referred to is F1, inter se mating. Accordingly, suitable first generation cocks are mated to selected hens; as always based on SOP. These progenitors are grouped to avoid inbreeding and kept distinct in two groups. The offspring of the F1, inter se matings, the F2 generation, are the "double cross" in the line. The objective in the F2 or double cross, generation is to obtain cockerels, which will be purest in color, and superior to both progenitors of both first crosses.[/FONT]
[FONT=Times New Roman, serif]It takes several years for the best individual first-cross cockerels to be singled out. The best cockerel of the first F2 “double cross” of the progenitors becomes the Alpha Cock (AC). Without question he must be superior in all aspects of body, size and color.[/FONT]
[FONT=Times New Roman, serif]From this AC, planned mating continues using the AC crossing back to the original progenitor hens creating an Alpha one first generation F1A. From this generation are selected the two best of AC sons which are place back with the progenitor hens of both groups producing AC FA1 “double cross” generation. Now taking hens from the first generation AC FA1 double cross back to AC to produce second generation AC FA2 double cross. The hens from this cross are then taken and separated and culled into two classes and crossed with AC's first generation sons. (Note here it would take too long to explain the re crossing of AC's grandsons back to the grandmother's but the math is the same as explained above.) The results after usually 10 or more generations is the creation of two stable, separate but genetically identical lines.[/FONT]
[FONT=Times New Roman, serif]These lines tend to weaken and so Grading-back is necessary by drawing stock from the Graded-up stock and this is where it gets a bit shaded. You have to either have a separate line of WPR completely unrelated to the two strains created or you had better know the Grading-up line of stock you will chose your new cock to Grade-out your strains.[/FONT]
[FONT=Times New Roman, serif]Grading-up is the system of breeding, whereby, generation after generation of standard bred cocks are used on the similar standard bred hens of the same flock but where the cocks are unrelated to the females major improvement, through heterosis, results in the F* generation. Performance and type approaches that of the purebred in the succeeding generations. After the sixth generation, the graded flock will be genetically similar to the in an in bred generations. Important consideration in a grading-up program is that the cocks used should be performance tested and the production level must be high.[/FONT]
I wanted to post this message from the other string I was answering Robert's question on because it goes along with the SOP breeding discussions we've been having here and I'm not sure how many folks here are following the string I wrote this in. I misunderstood Robert's question but it raised a complex breeding issue that still holds validity and worthy of consideration for all serious breeds. So if you didn't read the other string and have any interest just click the above spoiler.