Objective This experiment investigated the effects of adding different weights of residual red dates to the diet of lactating cows in the late stage of lactation on rumen fermentation parameters and microbial diversity.

Methods Selected 32 Holstein cows with similar breeds, ages, parity, and lactation days (200 ± 5) d in the late lactation stage, randomly divided them into 4 groups, with 8 cows in each group, and divided them into a control group and groups with 5%, 10%, and 15% residual red dates added. The experimental period was 37 days, including a pre feeding period of 7 days and a main trial period of 30 days. On the 30th day of the experimental period, 3 experimental cows with milk production close to the group average were selected from each group, and rumen fluid was collected orally to measure fermentation parameters and microbial diversity.

Results The pH of the group treated with defective red dates was higher than that of the control group (P>0.05), and the concentrations of acetic acid, propionic acid, and valeric acid were higher in the group treated with 15% defective red dates than in the control group, as well as in the groups treated with 5% and 10% defective red dates (P>0.05); Four groups of samples obtained a total of 2 668 operational taxonomic units (OTUs), of which 1741 were OTUs; The Angiotensin-Converting Enzyme index and Chao1 index of the group with 5% defective red dates added were higher than those of the control group, the group with 10% defective red dates added, and the group with 15% defective red dates added (P>0.05). The Simpson index and Shannon index of the group with 10% defective red dates added were higher than those of the control group, the group with 5% defective red dates added, and the group with 15% defective red dates added (P>0.05). The dominant bacterial groups at the phylum level in each group are Firmicutes, Bacteroidetes, and Verrucomicrons. The relative abundance of Firmicutes in the group with 5% defective red dates added was higher than that in the control group, the group with 10% defective red dates added, and the group with 15% defective red dates added (P>0.05). The group with 10% defective red dates added was higher than the control group and the group with 15% defective red dates added (P>0.05); The dominant bacteria at the genus level are Prevotella, and Ruminococcus. The relative abundance of Prevotellace-UCG_003 in the group with 10% defective red dates added was higher than that in the group with 5% defective red dates and the group with 15% defective red dates added (P>0.05). The relative abundance of Prevotellace-UCG_003 in the group with 15% defective red dates added was significantly higher than that in the control group, the group with 5% defective red dates added, and the group with 10% defective red dates added (P<0.05). The group with 10% defective red dates added was significantly higher than the group with 5% defective red dates added (P<0.05).

Conclusion Adding 5% to 10% residual red dates to the diet of lactating cows does not affect the richness and diversity of rumen microbiota in lactating cows; When adding 15% defective red dates, it will reduce the richness and diversity of rumen microbiota in lactating cows, change the structure of rumen microbiota in lactating cows, and increase the relative abundance of Bacteroidetes and Proteobacteria.