Keith,we both have some of Fred Zillichs' bloodline and yes a few years back ]some Buff Rock was used sparingly for new blood and size by Fred.Freds stock is a very high percentage Leghorn blood,you have to look hard for some minor defects left from the dash of Rock blood,like shorter main tails,shorter sickles,slight red in earlobes,slight fluffiness, more broodiness,or slight tint of eggs.On the plus side there is back width,good breasts,frames,sturdy legs,stature and size.
I prefer long tails,lesser sickles and saddles and the only way to keep that trait is to let my bloodline concentrate or dominate the blood percentages.Keeping my main male line,lineage unbroken is one way I like to do it.Good breeders have to work in new blood from time to time,and in my nearly 40 years with Buff Leghorns I have done so a 1/2 dozen times or more.Most breeders do outcrosses,and if done right with persistence, it is beneficial.Sometimes a bloodline will work well,other times not.I look at it as a way of getting a wider gene pool,reducing inbreeding depression,and adding traits I lack or want strengthened.What it boils down to is our selections for the breeding pen and not narrowing (bottlenecking) to close by keeping too few males. Dan Honour