Developmental stability in different genetic stocks of white rock chickens

Asymmetries were determined for several bilateral traits in females from a line of chickens selected for 39 generations for low 56 day body weight (LWS) and in a subline of LWS where selection had been relaxed for four generations (LWR). Because of reduced food intake under ad libitum feeding, some LWS females do not commence egg production, a condition that can be overcome by relaxing selection for a generation or two. Bilateral traits, measured at 240 days of age in LWS non-layers, LWS layers, and LWR layers, were shank length and diameter, distance between the auditory canal and the posterior junction of the upper and lower mandible, and weight and length of the first primary wing feather. Other traits measured were body weights at 56, 168, and 240 days of age and age at first egg. Fluctuating asymmetry, a good overall measure of developmental stability, was lower in the relaxed than selected line. Means of relative asymmetries were also lower for LWR females than LWS layers and nonlayers which were similar.