IntroductionMn, which is an essential trace mineral for all animals, has functions in skeletal system development, carbohydrate and lipid metabolism. The aim of this study was to clarify the effects of different manganese (Mn) sources in basal diets on nutrient apparent digestibility, fecal microbes, and mineral elements excretion before and after weaning.MethodsA total of 15 Holstein heifer calves (6-week-old, 82.71 ± 1.35, mean ± standard error) were randomly designed into three groups (five each): no extra Mn supplemented (CON), 20 mg Mn/kg (dry matter basis) in the form of chelates of lysine and glutamic acid in a mixture of 1:1 (LGM), and 20 mg Mn/kg (dry matter basis) in the form of MnSO4. All calves were weaned at 8 weeks of age. The experiment lasted for 28 days (14 days before weaning and 14 days after weaning). Dry matter intake (DMI) was recorded daily. The animals were weighed by electronic walk-over, and body size indices were collected using tape on days −14, −1, and 14 of weaning. The feces of calves was collected to measure the apparent digestibility of nutrients (acid insoluble ash was an internal marker) and bacterial community on days −1, 1, 3, 7, and 14 of weaning. Fecal mineral concentration was determined by inductively coupled plasma emission spectroscopy on days −1, 1, 7, and 14 of weaning.ResultsThe results showed that, compared with the CON group, adding LGM to diets containing 158.82 mg/kg Mn increased the apparent digestibility (P< 0.05). The Chao 1 and Shannon index of fecal bacteria decreased at day 1 in the LGM and MnSO4groups and increased after weaning. The PCoA results indicated that the LGM group was distinctly separate from the CON and MnSO4groups during the whole experimental period. Significant differences (P< 0.05) were observed in the relative abundance of two phyla (ProteobacteriaandSpirochaetota) and eight genera (Alloprevotella, Prevotellaceae_UCG-001,ClostridiaUCG 014, RF39, UCG-010,Pseudomonas, Ralstonia, andTreponema) in three groups. Moreover, the LGM group showed less excretion of Fe, P, and Mn than the MnSO4group.DiscussionIn summary, 20 mg Mn/kg diet supplementation improved nutrient digestibility, changed the fecal microbial community, and reduced mineral excretion. Organic Mn supplementation in the diet had more advantages over the sulfate forms in weaning calves.