Percent residual food consumption (PRFC) was recorded for cocks from a highly productive strain of layers and compared with PRFC recorded for old hybrid hens. In addition, possible causal traits to PRFC were studied on the cocks. PRFC is defined as the difference between the recorded and the expected food consumption as a percent of the expected. The phenotypic variation in PRFC among cocks was found to be large (SD=6.19%) and the heritability of PRFC was estimated to be 0.37 ± 0.29. Factors causal to the variation in PRFC were differences in fat content, behavioural pattern and heat loss in metabolic processes. Including PRFC, recorded on cocks in one four-week period after 24 weeks of age, as a selection criterion in an index may be suggested to improve the efficiency of food utilization in layers.