Selection against Body Weight in Small Populations of Chickens

Abstract

Four generations of selection were conducted in small populations to reduce body weight of chickens at 150 days of age. The base population was divided at random into three groups. One of those was directly selected against body weight (small body weight line), and the second was selected by a selection index designed to reduce body weight but to increase egg production to 270 days of age and to hold egg weight constant (index line). The third group was maintained as a control line.
Although effective selection responses were observed in both of selected lines, the responses were higher in the small body weight line than in the index line for both characters of body weight and egg production. It was contrary to expectations. The effective selection differentials were smaller than the expected selection differentials in both selected lines. The realized heritability for body weight at 150 days of age was about 0.3.
Changes of gene frequencies at four blood group loci were examined in each line. In the control line there were observed no obvious changes in the gene frequencies over four generations. In the selected lines, however, the gene frequencies showed a consistent trend of increase of higher frequent genes. The trend was much conspicuous in the small body weight line.