A good uniformity is important for a proper management of breeder flocks. If uniformity is high it means that many birds will be in the same stage of development, which makes management actions as light stimulation and feed increases more effective.

Grading is a useful tool to improve uniformity. With grading groups of smaller and bigger birds are formed, and as the feed amount can be adjusted to the development of the birds they can slowly be adjusted to a uniform overall flock.

However, a good uniformity is as well related to uniformity in frame size as it is to uniformity in body weight by itself. When there is a huge variation in frame size, a uniform body weight will not necessarily mean that the birds are uniform in development, as smaller birds will have relative for their size bigger body weights, and vice versa. It is therefore important to get a uniform frame size as well.

A lot of the (lack of) uniformity in a flock is already determined very early in life. Although the birds are genetically almost identical and the feed is also uniform for all the birds in the flock, individual differences as chick quality, , bacterial pressure, temperature differences etc will influence the early feed intake and therefore growth of the bird, and therefore the early development.This means that differences in size is already established very early in life, and will not easily change afterwards, if no actions are taken.

As frame size especially develops early in life, it is important that grading should done as early as possible. If grading is done later in life, the body weight of the groups of birds can be adjusted towards the average, but the frame size will remain smaller or bigger, dependend on the early development of the birds. As the final frame size is already more or less determined at an age as young as 7-8 weeks, grading should be done at a moment when there is still enough time to correct the frame size.

A good practice is to try to finish the grading before the age of 28 days, or even earlier if that is possible. Although it seems easier to do it at an older age as the differences in body weight between the individual birds are more pronounced, the fractional differences are already established after a few weeks, which makes it possible to do an effective grading.

If grading is done early, there is more opportunity to do a gradual adjustment of feed and body weights to get the body weights of the different groups more uniform. Also the dominancy of the bigger birds will have not established that much to make it difficult to mix the groups at a later age. One other aspect is that with earlier grading, we normally see that especially the number of bigger birds in the flock seems to diminish, probably because of the more equal dominancy as described before.