To increase uniformity in rearing, flocks of breeders can be graded in weight groups, for instance in big, average and small birds. It is advisable to do it early in life as at that moment the frame size can still be corrected, but sometimes it is necessary to do it again later in rearing. To get the birds more uniform, we often correct the feed amounts for the different groups to get the total flock more uniform. But what is a good correction, and how to choose the right feed amount?
The goal of the adjusted feed program is to get the birds slowly back on the standard body weight, so we need to correct the feed amounts with little steps. But when we think about our weight groups, we have to realize that the different groups were not eating the same, as otherwise they would have had the same body weight. Especially for the heavier groups and then especially for the males (although it holds for the females as well) this can be a problem.
If we take as an example a flock of broiler breeder males of 12 weeks of age which is eating 75 grams of feed per day and is weighing 1700 gram. We grade the birds into three groups, average, small and big. The big birds are most probably big because they were eating more than the average 75 gram, for instance 85 grams. As a result, the small birds had less to eat, only 65 grams, and got underweight.
If after grading we put all the groups on 75 grams of feed, we actually decrease the feed for the biggest group from 85 to 75 gram! As a result the birds will get more competitive, start fighting more for feed and as a result might lose uniformity again. If we cut the feed for the bigger group under the standard to correct them quickly, we make the problem even worse.
This problem is occurring especially in males and especially in the group with large birds, as they are more competitive and are actually facing a reduction of the feed amount. It might therefore even be necessary to increase the feed for that groups slightly, to make the relative reduction in feed and resulting competition less, and in that way maintain the uniformity in the group.