Improvement Breeding
By Don Schrider
Breeding’s first role is to produce the next generation, but doing so without any planning leads us into a situation where all the birds are closely related and results in loss of productivity and vigor over generations. We can divide breeding into two main functions—maintenance and improvement of productive attributes, and maintenance of genetic diversity within our flock. I will refer to these two aspects of breeding as "breeding for improvement" and "conservation breeding" respectively.
Most available information on breeding focuses on improvement breeding. Essentially improvement breeding is often described as breeding "your-best-to-your-best." In actuality, culling inferior birds and selecting superior birds results in improvements to a flock over time. Good improvement breeding need only focus on mating together birds that share good traits to cause them to occur more frequently in the flock, as well as making sure that mated birds do not share the same faults so that faults occur less frequently. We call these two aspects of improvement breeding "emphasizing good traits" and "offsetting faults."
Conservation breeding has to do with making decisions that ensure there is enough diversity in the flock such that it can be bred for many generations without fear of the individuals becoming too closely related. So conservation breeding focuses on managing how related each individual is to other individuals in the flock; based on relations, who is mated to who; and ensuring that some individuals within the flock are as unrelated as possible. As we design a breeding program for our flock, conservation breeding decisions are going to play a key role in allowing us to breed for many generations without losing diversity.
It should be clear that as long as we can only maintain one flock of chickens, we can only breed for one season without mating related individuals, and, as seasons progress, more and more birds in the flock will become closely related. Nowhere is this more clear than in a small flock with only one rooster—genetically he is half the flock, as every offspring gets half his genes. This simple example illustrates that to maintain genetic diversity we need to use as many males as possible, and limit how often they are used.
As we breed our flock, there are relationships we try to avoid and others that can be used. For instance, brother to sister matings tend to be the most intense form of inbreeding. However, sire to offspring and dam to offspring are less intense. How can this be? A parent only gives its offspring half of its DNA, the other half coming from the other parent. Whereas, brothers and sisters can be nearly identical in DNA and this type of mating sometimes results in loss of size and increase in faults—like crooked beaks. More distant relationships would include cousins, aunts or uncles, and even 2nd cousins. Ideally, we would like our matings to be largely more distant relationships, however, the occasional more closely related mating is acceptable.
