OTP decreased abdominal fat yield, subcutaneous fat thickness,intramuscular fat width and serum TG concentration in ducks, which may be partly due to the enhancing effect of caffeinein OTP on lipolysis in adipose tissue, and to the inhibitory action of some other substance in OTP on pancreatic lipase activity. Coarse OTP had no significant effect on fat deposition, implying that bioavailability of lipolytic componentsin coarse OTP was less than those in fine OTP. It has been reported that the bioavailability of tea components can be improvedby reducing the particle size of green tea in rats . Tea catechins are present in mesophyll butnot epidermal cells , thus coarse grinding may not be able to thoroughly break up the mesophyll cellwalls of tea leaves. The optimal particle size of OTP for reducing fat deposition in meat ducks needs further investigation.Supplemental OTP with different sizes decreased drip loss of pectoralis major muscle. This can be explained by theantioxidant activity of OTP, which can decrease lipid oxidation, enhance integrity of cellular membrane and consequentlyimprove the water-holding capacity of meat . However, dietary treatments did notaffect meat colour, pH values, cooking loss or shear force, which is consistent with previous research .The antioxidant activity of oolong tea has been reviewed previously . In this study, fine OTP increasedSOD activity and decreased MDA content in serum, which may contribute to lower lipid accumulation . Deng et al. also reported that dietary green and black tea increased SOD activity and decreased MDA contentin serum of rats, whereas tea particle size was not reported in their study. The lack of response to coarse OTP is consistentwith the data of fat deposition.