Breeders of all classes of livestock spend years putting together a stud and gathering as many of the desirable genes together (linebreeding) only to lose all their gain when going outside of their stud to bring in new blood or what is called an outcross. Whilst I hope you are bringing in this bird to improve a feature lacking in your stud and not just because he/she is the brother/sister of a show winner, you are bringing in addition to the desirable feature, a lot of hidden undesirable genes. The genetic makeup of birds in their chromosomes means that all the undesirable genes are still present. It is just that they are not “switched on”. When mixed with the genetics in your stud there is every possibility that a number of them will be switched back on and become evident and your gains will be eliminated.
The way to minimise this is to go back to the stud that your birds originate from and while you are bringing in the desired feature, a lot of the hidden genes are the same as what you have and you will not lose the uniformity you have built up as much.
The most effective way to do this and seldom practised in NZ, is for two or three studs to work in together and swap or loan birds. Over time your studs will all have similar genetic bloodlines but sufficiently different to reduce inbreeding depression and with different breeders placing priority on different features the studs should have features your stud is lacking in.
How you achieve the loan or swap is up to you but generally if the bird breeds four chicks then you split them between you. You can ring them alternately with each others rings or draw them out of a hat at the end of the season. It is up to you. It may be that you simply just swap or loan the adult birds.
It is not something commonly practised, but I would urge you all to consider. I know of one case in NZ where is has been practised successfully between two studs ever since the British importations. It is a win win situation for both parties and financially a lot cheaper too except for the wine consumption during the discussions!