Feed efficiency is a major driver for sustainable pig breeding, saving feed resources and lowering environmental impacts. In pigs, contrasted feed efficiency are associated to differences in feeding behaviour, with a reduced feeding time in more efficient pigs. Studies in human and rodents have shown that aligning feed intakes with day/night cycles is essential to optimize energy metabolism and body composition. In pigs, the role of daily feeding rhythms on feed efficiency remains to be explored. In our study, temporal feed intake data of about 4,000 pigs from two divergent lines selected for residual feed intake (RFI) were recorded by automatic feeders. Feeding rhythm was mainly distributedduring the day, with two peaks, in the morning and in the afternoon. Significant differences were reported between lines for this pattern, with pigs from the more efficient line eating proportionally more during the peaks (+ 73 g/d and +89 g/d, P0.30±0.04), and showed significant genetic correlations with daily feed intake and RFI. The sequence variants detected in the founders of the two lines were then imputed to all breeding pigs of the lines previously genotyped for a 60K medium density SNP chip. The allelesfrequencies were computed for the genomic variants segregating in the ten core clock genes regulating circadian rhythm. Changes of allele frequencies with selection were tested separately in each line. Significant responses to selection were pointed out in the ARNTL and CLOCK genes in the less efficient line (P<0.05 genome-wide level), suggesting a molecular basis for the differences of feeding rhythm detected between the lines. These results indicate that the genetic variability of feed efficiency in pigs could be related to alterations in circadian rhythms.Read less <