When we do grading, either during or at the end of rearing, we have to be careful with the actual feed amount that we are giving.

Especially when at the end of the rearing period the smaller birds are taken out of the flock and placed separately, we have to realise that by doing this, we are changing the feed amount for the other birds as well.

To illustrate the effect, we can consider an imaginairy flock of 9000 female broiler breeders, which at the end of rearing are 2000 g in body weight and get 100 g of feed on average.

We can assume that all these birds are eating exactly the same, but in reality that is of course not the case. If it would be the case, all birds would weigh the same, which is obviously not the case.

So lets assume (for simplicity reasons) that within the flock of 9000 birds we have three different groups.

3000 birds are indeed 2000 g in body weight and eat 100 g of feed

3000 birds are 2200 g in body weight and eat 110 g of feed

and 3000 birds are 1800 g in body weight and eat 90 g of feed

To get the birds evenly in production, we take out the 3000 small birds, place them in a separate house, give them and adjusted feed profile and an adjusted light schedule, as the birds are less developed.

This means that the remaining flock consists of 6000 birds, 3000 birds that have the average body weight and the average feed intake, and 3000 birds that are heavier in body weight and eat more feed. On average, the flock is 2100 g and eat 105 g of feed.

This means that if we do take the smaller birds out of the flock, we have to actually increase the feed for the remaining birds, to not let them drop in feed quantity! If we would keep the flock on the average feed amount of 100 g as was the level before the grading, in this imaginairy flock we are dropping the actual feed intake with 5 g!

Of course in a real life situation it will not be so easy to calculate the real feed intake as in this example, but its good to realise that when we do grading, we do not only have to adjust the feed amount for the groups that have been separated, but also for the groups that remain as "normal" birds, to avoid problems with growth and development.