In search for some more information on genetics I bumped upon the book "Principles of genetics: an elementary text, with problems" by prof. Edmund W. Sinnott and L. C. Dunn. Published in 1925 it is an old book by current standards but it stems from the time when heredity and selection found their scientific base.
On page 349 the authors touch upon The Breeders Problem:
I would like to rephrase, modernise, append and correct these points for the contemporary budgerigar breeder and call it The Breeders Challenge(*).
What is your ambition as breeder? Do you just want to breed budgerigars or do you want to breed quality budgerigars? This article is for the latter one. The definition of quality varies. Every person, be it breeder or judge, has his or her own opinion on how a budgerigar should look like. Over time the perception of the perfect bird also changes.
Before you can start with the breeders challenge you must have an idea of the ideal budgerigar looks like. If you want to win shows your ideal must match that of the judges. Some top breeders have a vision on how the budgerigar should evolve and look ahead. For most of us it would be saver to just go for the current ideal.
What is important to a true breeder is not the quality of a bird in a show cage but the value it has in the breeding cage. A true breeder does not want to have top birds; he or she wants to breed them. It may seem like a subtle difference but I feel it is a very important one.
What makes a top breeder is the way he or she assesses a bird. Top breeders see the subtle differences that will become important characteristics for breeding even better birds in the future. For instance a top breeder can look at a bird and make abstraction of the feather length and asses its potential as parent. Top breeders have "the eye". They know the difference between quality and breeding value. "Breeding value": we've hit the most important concept in this article.
Assessing breeding value is the most difficult but also the most important part of the breeding challenge. The entire breeding season is determined by the choice of the parent.
I'm not going to write up a nice guide titled 'how does a good parent look like'. I'm not experienced enough for that. It may even depend from stud to stud. You should ask those top breeders and take a look in their breeding cages for what they use as parents. One important issue with budgerigars is feather length and concerning this I have one recommendation to make: don't be fooled by buff birds. Buff birds generally look bigger and better then yellow birds but buff is not such an important trait when it comes to breeding value. Arguably it could very well be a counter argument as it is common knowledge that buff birds produce less offspring. Isn't it better to pair up two medium buff birds and get offspring of which some are buff than to pair up two buff birds that will never have offspring? When selecting try to imagine your non buff birds with a buff feather. When you do that directional head feathering, balance and so on become more important and you will be able to make abstraction of feather length.
So your breeding season is at an end and you look at your flight. Which birds will you keep for the next breeding season? Selection always starts with assessment but that is just the start. Remember that you want to select the best parents and not the best birds.
An assessment is based on the physical traits of a bird. The physical traits are correlated to the breeding value but there is some error on it. The only real test for the breeding value of a bird is the offspring.
Group your birds by parents and assess them all individually. It is important to assess all the young of a pair and not just the best one. Ask yourself the following questions for every pair:
You will now have an idea which pairs are good pairs and which pairs are bad and hopefully you will have an idea of the breeding value of your parents for different characteristics. Use this information when selecting the young! This means also selecting on pedigree. It is a vital tool at complementing the assessment of a bird. As a rough rule of thumb you can say that in general the breeding value of a bird will be closer to halfway between the assessed quality of the bird and the assessed quality of the parent pair then to the assessed quality of the bird as such. Or in other words: the lesser birds of a pair will often be better than they look and the better birds of a pair will often be worse then they look. As a consequence you will end up selecting more birds from the better pairs then you would have if you had only selected on the assessed value of the birds.
I should not close this part on selection without saying that you must always remember that the more young you breed, the more choice you have when selecting and the better the next generation will be. Fertility is paramount for a good stud.
Before I say anything else about mating systems: the previous paragraphs are a several times more important then this one. As long as you select the best birds for breeding even the worst mating system will do reasonably well, good even. On the other hand if you select all the wrong birds no mating system can cope with that and it will be a disaster. A good mating system can only help if you do reasonably well at selecting the best parents and it will protect you partially against the selection mistakes.
I can't touch upon mating systems without mentioning inbreeding. Inbreeding is mating relatives and as such is not a mating system. Every mating system however does involve inbreeding at one level or another. In some mating system this is intentionally and in others it is a side effect. There are articles saying that inbreeding is good but it is very hard to find articles convincingly explaining why it is good. I will begin with the bad effects of inbreeding.
Experience and many experiments lead to believe that inbreeding leads to inbreeding depression. Inbreeding depression is mostly apparent in the form of lower fitness, higher susceptibility to diseases and decreased fertility. Conversely crossing unrelated inbred animals often leads to robust and fertile offspring. Note that there are exceptions so inbreeding doesn't automatically leads to inbreeding depression but it probably will. I said before that fertility is paramount so we must be careful with inbreeding.
Another negative effect of inbreeding is that it diminishes genetic variation and a lower genetic variation leads to a smaller selection result. I'll explain. Because of inbreeding the birds will more and more share the same genes. In other words the genetic differences between individuals become smaller and the positive effect of selecting the better ones becomes smaller. So your stud doesn't advance anymore despite rigorous selection. There is an easy solution to this problem that is called out-cross. Be sure to introduce one or more out-crosses well before your stud stagnates.
So are there any good points about inbreeding? Yes there are. First for practical reasons: when you only have one good bird and you will have to use inbreeding to use its full potential. Inbreeding can also be used to expose low frequent recessive genes. I can best explain them by example:
Ex. 1: one good bird
You've just spent your savings on that super bird from that top breeder.
You would have liked to buy 10 pairs from that breeder but your budget
barely sufficed for one cock. This cock is much better then your own birds
so in a few years you want your stud to be mostly comprised of its genes.
You will have to use inbreeding - quite high inbreeding even - to achieve
this: cock x daughter, half brother x half sister, etc. Without inbreeding
this would be impossible.
Ex. 2: exposing low frequent (good) recessive genes
Suppose you want to breed blue birds but you only have green birds in your
stud. You suspect that some of your birds are split blue but you have no
idea which ones. Using inbreeding you can raise the odds that two
splits are paired because a relative of a split has a higher change of
being split itself. Replace 'blue' with a 'good recessive gene' and you'll
see that by using inbreeding you can exploit those good recessive genes in
your stud. Note that inbreeding does not know the difference between a
good or a bad gene so you will have to pay careful attention not to
develop bad genes.
As one of the bad points of inbreeding I mentioned that inbreeding decreases the genetic variability. But strangely enough you can diminish this effect dividing your stud in separated subpopulations. When you divide you stud in two separate lines the inbreeding increase inside the lines will be twice as high as opposed to mixing the two lines. But you can prove using some mathematics that that inbreeding level in the stud as a whole does not increase as much when you subdivide. This means that the genetic variation within your stud as a whole does not decrease as much when you subdivide.
By the combined effects of less loss of genetic variation and the exposing of low frequent good recessive genes the above method of dividing your stud in different smaller lines might be a very good one to practice.
I'll give an example of a starting beginner that just bought 3 pairs (from the same breeder) and has the intention of eventually breeding with 15 pairs:
Year 1
cock A x hen B
cock C x hen D
cock E x hen F
Year 2
Line 1 (5 pairs)
cock A x hen (CD)
cock (AB) x hen (CD)
cock (AB) x hen (CD)
cock (AB) x hen (CD)
cock (AB) x hen (D)
After each breeding season per line the 5 pairs are sorted according to their breeding value (i.e. the average assessment of their young): Pair 1 > Pair 2 > Pair 3 > Pair 4 > Pair 5
For the next breeding season you order the young per pair from best (left)
to worse (right) and organise the 5 pairs like this:
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
2 2 2 2 2 2 2 2
3 3 3 3
4 4
5
Squashed together on one line the order becomes:
1213121412131215121312141213121
There might be gaps since you probably won't breed 16 young from your best pair. Gaps are no problem it's the order that counts. Also notice that the lesser pairs have fewer representatives in this line-up.
To create your pairs for next year take the bird most to the left and go
down the line until you find a suitable partner. A suitable partner would
be one that has the opposite sex and isn't a sibling. If everything
matches perfectly you'll get these pairs:
Best from pair 1 x best from pair 2
2nd best from pair 1 x best from pair 3
3rd best from pair 1 x 2nd best from pair 2
4th best from pair 1 x best from pair 4
5th best from pair 1 x 3rd best from pair 2
You'll notice that this resulted in 5 young used from the best pair (pair 1), 3 from the 2nd best pair (pair 2), 1 from both the 3rd and 4th best pair (pairs 3 and 4) and none from the worst pair (pair 5).
In this system you will probably want to substitute the 3rd from pair 2 with an out-cross. This can be a real out-cross or a bird from one of the other lines depending on your budget or what the line needs.
The breeders challenge can be summarized as:
0. Vision of what the ideal budgerigar is.
1. Assessment of a bird for the important characteristics of a high
breeding value
2. Selection of the best parents by complementing the assessment with
information from relatives.
3. Mating the birds according to a mating system.
(C) Bert Raeymaekers