line breeding

It depends on the needs of the flock. when breedlng animals, first I talk to the breeder of my birds or ( insert species). I find out which breeding systems he/she used to create the creatures. How closely the birds are related. Is this a closed gene pool, or is there and outcross close up in the pedigree. What influence did any one breeding program have on the gene pools creation and maintenance? What does the breeder feel are both the immediate and long term needs for his/her gene pool? These answers will help you understand which breeding programs are best for your animals. Be they mammals, birds or? Many breeder use a variety of programs depending on the needs of their gene pool. In poultry, any outside blood is best brought in thru the female side. That way if the cross doesn't nick, one hasn't polluted the whole gene pool thru the use of a male.
A closed gene pool is more than just a gene pool which hasn't been outcrossed. It is a gene pool which has been maintained within itself for so long that any unconsidered outcross is more likely to create problems than enhance the gene pool. The genes in a closed gene pool are very stable and do not take kindly to being manipulated by anything but than an extensively researched and well educated insertion of foreign blood. This foreign blood should be from a related gene pool and no more than 25% of it should be unrelated to the closed gene pool. It should be added in thru the female side. Then the get from that breeding be bred back into the closed gene pool to re-stablize the closed gene pool with the addition of whatever plusses were brought in from the foreign blood.
This is where many novices err. They believe they need to create "biodiversity" and found their flock by crossing strains. In closed gene pools and veteran line bred superior flocks ( both sometimes the same thing) this upsets the equilibrium of the gene pool and the novice spends years trying to re establish it or plain gives up. research is your friend. The breeder of your birds and the history of the breed are also.
Best,
Karen
Waterford English Light Sussex
in western PA, SA