Abstract: [Objective] The aim was to explore the effect of adding lactose to diet on lactation performance and rumen fermentation of dairy cows. [Method] Twenty lactating China Holstein cows with similar parity and body condition were randomly divided into four groups, namely, control group, experiment group I, experiment group II and experiment group III. The control group was fed with basic diet, and experiment groups I-III were fed with 5%, 10% and 15% lactose on the basis of basic diet, respectively. The preliminary experiment lasted for 7 days and the formal experiment lasted for 30 days. Milk components and rumen fermentation parameters were determined by milk component analyzer, colorimetry and gas chromatography respectively. [Result] Compared with the control group, the dry matter intake, milk yield and routine milk components of dairy cows in each experimental group had no significant effect (P > 0.05), but the milk yield increased with the increase of lactose dosage, and the contents of milk fat, milk protein and lactose also increased. Compared with the control group, the milk fat rate of dairy cows in experimental group II and III increased significantly (P < 0.05), and the lactose rate in experimental group I, II and III increased significantly (P < 0.05). Compared with the control group, there were no significant differences in rumen pH, total volatile fatty acids, ammonia nitrogen concentration and lipopolysaccharide content among the experimental groups (P > 0.05). The contents of acetic acid and isobutyric acid in the rumen of the experimental group III were significantly decreased (P < 0.05), while the contents of butyric acid in the rumen of the experimental group II and III were significantly increased (P < 0.05). [Conclusion] Adding lactose to the diet can improve the lactation performance of dairy cows and promote rumen fermentation of dairy cows during lactation.

Key words: diet, lactose, cow, lactation performance, rumen fermentation