Abstract: The aim of this study was to investigate the effects of dietary supplementation with manganese glycine (MG) on gut microbiota and laying performance in aged laying hens. A total of 720 70-week-old Hy-Line Brown hens were assigned equally to four groups with six replicates of 30 birds each. No additional manganese (Mn) was added to the basal diet (the measured Mn content was 21.77 mg·kg^-1). The hens were fed basal diets supplemented with 120 mg·kg^-1 of Mn from manganese sulfate monohydrate (MSM), or 40, 80, or 120 mg·kg^-1 Mn from MG. The measured Mn contents in the experimental diets were 144.46, 57.84, 96.97 and 135.59 mg·kg^-1, respectively. The experimental period was 12 weeks (70-82 weeks). The results showed that, dietary supplementation with 40 mg·kg^-1 Mn from MG resulted in higher laying rate than those observed in the 120 mg·kg^-1 MSM group and 80 mg·kg^-1 MG groups from 77 to 80 weeks (P <0.05). The laying rate of growps supplemented with MG from 70 to 82 weeks of age tended to increase (P= 0.071), while no significant difference was observed in other indexes of laying performance among the treatment groups (P>0.05). The Chao1 and Shannon indexes of cecal microflora in layers fed with 40 mg·kg^-1 MG were significantly higher than those in 120 mg·kg^-1 MSM group (P<0.05),and has the highest OTUs number, which indicated the highest diversity and richness of the microbial community. At the genus level, the top 10 bacteria were traced back to the phylum level, the Firmicutes relative abundance in the 120 mg·kg^-1 MSM group was significantly higher than that in the 80 mg·kg^-1 MG group (P<0.05). The microbial groups that played an important role in the 120 mg·kg^-1 MSM group were concentrated in the Firmicutes and Selenomonadaceae, the microbial groups that played an important role in the 80 mg·kg^-1 MG group were concentrated in the Spirochaetota phylum Spirochaetaceae family. The results of differential bacteria analysis showed that the relative abundance of Lactobacillus in the 40 mg·kg^-1 MG group was significantly higher than that of the 120 mg·kg^-1 MSM group (P<0.05), and the relative abundance of Paenibacillus, Massilia and Campylobacter in 80 mg·kg^-1 MG group was significantly higher than that of 120 mg·kg^-1 MSM group (P<0.05); Compared with the 40 mg·kg^-1 MG group, the 80 mg·kg^-1 MG group and 120 mg·kg^-1 MG group showed a decrease in the relative abundance of beneficial bacteria Megamonas, Lactobacillus, and Romboutsia (P<0.05), while the relative abundance of harmful bacteria Campylobacter increased (P<0.05). In conclusion, dietary MG supplementation with 40 mg·kg^-1 could improve the species richness, diversity index, increase the abundance of beneficial bacteria and the flora involved in the metabolic process of the intestinal microflora in aged laying hens, and improve the laying performance of laying hens in the later stage of the experiment (77 to 82 weeks of age).

Key words: manganese glycine, aged laying hens, laying performance, microorganisms