Abstract: 【Objective】 This study was designed to investigate the effects of rutin supplementation on milk yield, serum parameters and lactation-related hormones in lactating Chinese Holstein cows, and subsequently to offer reference data of optimum dosage of rutin for improving their lactation performance. 【Methods】 Twenty cows in their peak lactation were randomly divided into 4 groups and each was offered a basal diet supplemented with 0, 1.5, 3.0 or 4.5 mg rutin?kg-1of diet. The trial was 11 weeks, including an adaption period of one week and a ten-week experimental period. Milk yields were recorded every other day, and milk composition and vein blood samples were analyzed on the 5th, 35th and 65th days. Choose the best group and control group (0.0 mg?kg-1)to test serum biochemical indexes, immune indexes and lactation-related hormones. 【Results】 Compared with the control group, the cows receiving 3.0 and 4.5 mg?rutin kg-1 had significantly higher milk yields (P<0.05). No significant difference in milk yield was detected between the cow receiving 1.5 mg?rutin kg-1 and control group (P>0.05). The milk fat content of the cows receiving 1.5 or 3.0 mg?rutin kg-1 was lower than that of control group (P<0.05). No significant difference in the milk fat content was observed between the cows offered 4.5 mg?rutin kg-1 and control group (P>0.05). The contents of milk protein, lactose and milk non-fat solid matter did not differ significantly among groups (P>0.05). The serum lysozyme content of the group treated with 3.0 mg?rutin kg-1 was higher than that of control group (P<0.05), while the urea nitrogen on the 35th and 65th days was lower than the 5th day (P<0.05). This treatment group, alanine aminotransferase (ALT) levele from 22.88(IU?L-1)in 5th up to 25.38(IU?L-1)in 65th, the prolactin level reached 13.94 ng?ml-1 from 12.19 ng?ml-1, increased by 14.36%. The serum concentration of IgG, TP, ALB, GLU, Cort, AST and ALP in the cows receiving 3.0 mg?rutin kg-1 did not differ from that of control group (P>0.05). The serum concentration of estrogen (E2) and progestin (P) did not differ significantly among the treatments (P>0.05), but the serum progesterone showed an upward trend in rutin-supplemented cows compared with control. 【Conclusions】Dietary rutin improved the production performance of lactating Chinese Holstein cows with maintained milk quality, decreased blood urea nitrogen and increased serum lysozyme contents. The appropriate dosage for rutin supplementation was 3.0 mg?kg-1 diet.

Key words: rutin, dairy cows, lactation performance, serum parameters