Abstract: 【Objective】 This study aimed to investigate the effects of dietary supplementation with vitamin D₃ (VD₃) and 25-hydroxyvitamin D₃ (25-OH-D₃) on the tibial quality and intestinal microbiota composition of breeding ducks in late laying period. 【Method】 A total of 60 laying Pekin ducks (64 weeks of age) were randomly allotted to 3 treatments with 10 replicate pens of 2 duck each.The ducks were fed a basal diet with no vitamin D supplementation or supplemented with VD₃ or 25-OH-D₃ at 1 000 IU/kg of feed for 15 weeks.During the experiment,the average body weight and average daily feed intake were measured.After the experiment,the slaughter performance (pectoral muscle rate and cecal rate),plasma biochemical indicators and tibial quality of breeding ducks were determined.Additionally,intestinal morphology of the duodenum,jejunum,and ileum was evaluated,and cecal contents were collected for 16S rRNA sequencing to analyze microbial diversity. 【Result】 Compared with control group,①Dietary supplementation of VD₃ or 25-OH-D₃ had no significant effects on body weight,average daily feed intake,pectoral muscle rate,and cecal rate (P＞0.05).②Dietary supplementation of VD₃ or 25-OH-D₃ significantly increased plasma albumin content and the ratio of albumin to globulin (P＜0.05).③Dietary supplementation of 25-OH-D₃ significantly increased the tibial compressive strength (P＜0.05),dietary supplementation of VD₃ had no significant effect on the tibial compressive strength (P＞0.05).④Supplemented with either VD₃ or 25-OH-D₃ significantly increased the villus height of duodenum and jejunum and the ratio of villus height to crypt depth of duodenum (P＜0.05),reduced the muscle thickness of duodenum (P＜0.05).Compared with VD₃ group,dietary supplementation of 25-OH-D₃ significantly increased villus height and the ratio of villus height to crypt depth of duodenum (P＜0.05).⑤Dietary supplementation with VD₃ or 25-OH-D₃ significantly increased the relative abundance of norank_f_norank_o_Clostridia_vadinBB60_gorup and Rikenellaceae_RC9_gut_group (P＜0.05), significantly reduced the relative abundance of Roseburia,Erysielatoclostrium,Collinsella and Clostridium_sensu_stricto_1 (P＜0.05).The relative abundance of Desulfovibrio and Clostridium_sensu_stricto_1 in 25-OH-D₃ group was significantly higher than that in VD₃ group (P＜0.05). 【Conclusion】 Both VD₃ and 25-OH-D₃ could improve the tibial quality and intestinal morphology of breeding ducks in late laying period.Moreover,the effect of 25-OH-D₃ in improving tibial compressive strength,duodenal villus height and the abundance of flora related to energy metabolism in cecum was superior to that of VD₃.

Key words: vitamin D₃ (VD₃); 25-hydroxyvitamin D₃ (25-OH-D₃); tibial quality; intestinal morphology; microbiological composition