At 42 days of age, one male duck per replicate was randomly selected and weighed after feed deprivation for 12 h. Blood samples (about 5 mL each) were taken from wing vein and centrifuged at 3000 × g for 15 min at 4 °C to separate serum, which was frozen at −20 °C for further analysis. After blood collection, ducks were killed by cervical dislocation. Pectoralis major muscle samples were immediately taken and stored at 4 °C for meat quality analysis. Abdominal fat yield was calculated as the percentage of eviscerated weight. Subcutaneous fat thickness and intramuscular fat width were measured by a vernier caliper as previously described ( Wu et al., 2012).