ID2 and diabetes mellitus: Recently, it has been revealed that metabolism and circadian rhythms are highly intertwined physiological processes and their dysregulation can be associated with various disorders related to metabolism (i.e. diabetes) and appetite.24 It has been observed that ID2 knock-out mice present dysregulated circadian rhythms of feeding behavior and locomotor activity, and reduced weight gain regardless of high feed intake.25 The down-regulation of ID2 in high FCR chickens might affect the circadian rhythm of feeding behavior.