Comparison of body weight modification in chickens induced with the sex-linked dwarfing gene (dw) and by restricting access to food during rearing

Abstract

Related dwarf and normal female chickens were allowed restricted or free access to food from 8 to 18 weeks in order to compare the relative effects of genetic and nutritional manipulation of body weight on a number of egg production traits. Production records were collected from a total of 770 adult hens individually housed in a randomized block design. From 8 to 18 weeks dwarfs grew less efficiently than normals within both the restricted and fully fed groups. A relationship between body weight and age at first egg was shown, with dwarfs and restricted birds laying at later ages than their counterparts. Egg weight at 34 weeks was related to body weight, but dwarfs laid smaller eggs than their normal relatives even when compared at equivalent initial weights. A relationship was shown between body weight and egg weight when expressed as a proportion of body weight, which held for both genetic and nutritionally induced differences. Restricted feeding during rearing increased egg number to 66 weeks in normal birds but not in dwarfs, and dwarfs laid fewer eggs than normals. Age at first egg had a major influence on egg numbers.