Production traits of a Rhode Island Red layer line were analyzed to detect carrier animals with major genes that influenced a particular trait by applying the major gene index (MGI) approach. This method was used to examine the deviation of predicted breeding values between parents and offspring. Advantages of this method include its simplicity and time‐reducing, cost‐saving benefits compared with any other statistical approach for screening major genes. The layer line had been selected based on the desired gain index for 6 years at the National Livestock Breeding Center, Okazaki station. The line consisted of 125 sires and 2986 dams. Two economic traits as breeding objectives were studied – age at sexual maturity (ASM, days) and egg production efficiency (EP, %). The MGI detected nine sires and 23 dams as carriers with major genes for ASM, and five sires and 26 dams for EP. They were identified as important breeding stock, and pedigree information provided candidates possessing major genes with favorable effect at the founding of the selected layer line. It seems likely that the simple approach of the MGI could be a useful preliminary method for detecting carrier animals with major genes before applying molecular techniques on a sampled population to identify in more detail the existence of major genes and their carriers.