Abstract: 【Objective】 The research aimed to study the effects of dietary quercetin supplementation on egg quality and lipid metabolism of laying ducks at late phase of production. 【Method】 A total of 288 healthy Longyan laying ducks at 63 weeks of age with similar egg production rate were randomly divided into 4 groups,with 6 replicates of 12 ducks each.The ducks in control group were fed a corn-soybean meal basal diet,and the ducks in other treatments were supplemented with 100,200 and 400 mg/kg quercetin,respectively.The pre-trial period was 2 weeks,and the trial period was 9 weeks.During the pre-trial period,all ducks were fed the same basal diet.At the end of weeks 3,6,and 9,six duck eggs were selected from each replicate to determine egg quality.At the end of week 9,two ducks from each replicate were sampled via the wing vein to determine plasma lipid metabolism indexes.After slaughtered,the development of the liver and reproductive organs was assessed,and the liver was collected to analyze lipid metabolism indexes. 【Result】 ①Compared with the control group,dietary supplementation with 400 mg/kg quercetin significantly increased the egg-laying rate of ducks during the late laying period (weeks 4-6) (P＜0.05),exhibiting linear and quadratic responses with increasing dietary quercetin levels (P＜0.05).However,dietary quercetin supplementation had no significant effect on average daily feed intake,daily egg weight,feed to egg ratio,or egg breakage rate (P＞0.05).②Compared with the control group, at the end of the week 6, the addition of 100 and 400 mg/kg of quercetin significantly increased eggshell thickness in duck eggs (P＜0.05); the addition of 400 mg/kg quercetin group significantly improved the average eggshell weight, eggshell proportion and toughness at weeks 6 and 9, and throughout the entire late laying period (P＜0.05). At week 9, the dietary addition of 200 mg/kg of quercetin significantly improved eggshell strength, eggshell proportion and toughness (P＜0.05), and all these indicators showed an upward trend with increasing levels of quercetin added (P＜0.05).③With increasing dietary quercetin levels,ovarian stroma weight in laying ducks exhibited a quadratic response,initially decreasing and subsequently increasing (P＜0.05).Compared with the control group,dietary supplementation with 100 mg/kg quercetin significantly decreased ovarian stroma weight in ducks during the late laying period (P＜0.05).④Plasma LDL-C and hepatic TG contents decreased linearly and quadratically with increasing quercetin levels (P＜0.05),and plasma LDL-C content of ducks in the 200 and 400 mg/kg quercetin-added groups were decreased (P＜0.05),and hepatic TG contents of ducks in the 400 mg/kg quercetin-added group were decreased (P＜0.05) compared with the control group.⑤Based on eggshell toughness,eggshell ratio and breaking strength,the optimal supplemental levels of dietary quercetin were obtained by fitting the equation as 199.5,284.3,and 284.9 mg/kg,respectively. 【Conclusion】 Dietary quercetin addition could improve eggshell mechanical properties and lipid metabolism of laying ducks at late phase of production.Under the conditions of this experiment,the recommended quercetin supplementation level in the diet of late-phase laying ducks was 200-285 mg/kg.

Key words: quercetin; laying ducks; shell mechanical property; lipid metabolism; productive performance