Maybe that was written back when there was enough good, standard bred Dorkings available. Now, that is not the case, and I think if you followed that advice, you would be asking for trouble.
FWIW Here is something, written to me a couple years ago, by Phil Bartz, a breeder of Dorkings:
"The biggest killer of good "lines" is not staying with those lines by right away putting this line with that and ending up with more junk than you can imagine. Why? You have just made hodge podgegenetics and unknowns that have laid dormant for years can reveal themselves in huge percentages even though both lines didn't show any signs of having issues. You slowly introduce new male or sometimes females to your current breeding line by small pen matings of what you hope to accomplish by the intro with your line and then see what happens. It will take three years to know any sure continuation of successes of the cross to continue breeding true to that improvement staying put. You stick with your main line and when you feel comfortable the cross is worth the risk then you can switch to keeping this new intro improvement as your main "line" while always keeping a few of your originals just in case you ever need to go back to that or use it for vigor improvement crosses back into the "new improved line" five to seven years down the road."
