It was pulverized to powder with differenclet meanparti sizes categorised as coarse (357 m) and fine (16 m) by a jet mill . Mean particle sizes of oolong tea powder (OTP) were measured by the laser diffractionscattering method.One-day-old Cherry Valley meat ducks were obtained from a local hatchery and fed a commercial starter diet containing216 g/kg crude protein and 12.0 MJ/kg apparent metabolisable energy to 15 days of age. At 16 days of age, a total of 252ducks with similar body weight (744 ± 6 g) were selected and randomly divided into 3 groups with 6 replicates of 14 ducks (7males and 7 females) in each, and fed a control finisher diet (165 g/kg crude protein and 12.4 MJ/kg apparent metabolisableenergy) or one of two test diets supplemented with 1% coarse or fine OTP until 42 days of age. Ingredient compositionand calculated nutrient content of the basal diet were shown in Table 1. Ducks were allowed free access to pellet feed andwater on a plastic mesh that was placed 0.4 m above the floor. Continuous light was maintained and the temperature of theexperimental room was set at 26 to 28◦C initially and then reduced by 2◦C per week to a final temperature of 20 to 22◦C. At42 days of age, ducks were weighed and feed consumption was recorded by replicate to calculate average daily gain (ADG),average daily feed intake (ADFI) and feed conversion ratio (FCR, feed intake/weight gain). Mortality was also recorded.At 42 days of age, one male duck per replicate was randomly selected and weighed after feed deprivation for 12 h. Bloodsamples (about 5 mL each) were taken from wing vein and centrifuged at 3000 × g for 15 min at 4◦C to separate serum, whichwas frozen at −20◦C for further analysis. After blood collection, ducks were killed by cervical dislocation. Pectoralis majormuscle samples were immediately taken and stored at 4◦C for meat quality analysis. Abdominal fat yield was calculated asthe percentage of eviscerated weight. Subcutaneous fat thickness and intramuscular fat width were measured by a verniercaliper as previously described