Starvation induces skeletal muscle proteolysis in order to provide amino acids for hepatic gluconeogenesis or energy production, leading to the loss of skeletal muscle mass (Mitch and Goldberg, 1996). Previous studies reported the effects of fasting on the expression of genes involved in skeletal muscle proteolysis in chickens. For example, atrogin-1 mRNA levels increased in response to fasting in layer chickens (Nakashima et al., 2006). The expression of atrogin-1 and MuRF-1 mRNA was elevated in food-deprived broiler chickens (Li et al., 2011 and Ohtsuka et al., 2011). These findings suggest that atrogin-1 and MuRF-1 play important roles in fasting-induced skeletal muscle proteolysis in chickens as well as in mammals. Furthermore, atrogin-1 mRNA levels were found to be lower in broiler chickens than in layer chickens under ad libitum feeding conditions ( Nakashima et al., 2009). These findings raised the possibility that the regulatory mechanism underlying the gene expression of ubiquitin ligases in skeletal muscle differs between broiler and layer chickens, resulting in low skeletal muscle proteolysis in broiler chickens.