Simple SummaryThe stable microecological system in animal intestines is beneficial for the healthy growth of calves, and as zinc is an important trace element in the body, the question of how to better promote its absorption by the body has become an important research hotspot. Research has shown that an appropriate amount of zinc addition can promote the growth and proliferation of beneficial bacteria in the body’s intestines and inhibit the proliferation of harmful bacteria. This study showed that adding 80 mg/kg zinc amino acids to the diet can improve the growth performance, immune performance, antioxidant capacity, intestinal microbiota enrichment, and the intestinal microbial environment, as well as promote the healthy growth, of calves.AbstractThe aim of this study was to investigate the effect of dietary supplementation with zinc (Zn) amino acids at different concentrations on immunity, antioxidant capacity, and gut microbiota composition in calves. Twenty-four one-month-old healthy Angus calves of comparable body weight were randomly divided into three groups (four males and four females in each group) based on the amount of Zn supplementation added to the feed the animals received: group A, 40 mg/kg DM; group B, 80 mg/kg DM; and group C, 120 mg/kg DM. The experiment ended when calves reached three months of age (weaning period). The increase in dietary Zn amino acid content promoted the growth of calves, and the average daily weight gain increased by 36.58% (p< 0.05) in group C compared with group A. With the increase in the content of dietary Zn amino acids, the indexes of serum immune functions initially increased and then decreased; in particular, the content of immunoglobulin M in group A and group B was higher than that in group C (p< 0.05), whereas the content of interleukin-2 in group B was higher than that in the other two groups (p< 0.05). In addition, the content of superoxide dismutase and total antioxidant capacity in the serum of calves in group B was higher than that in group C (p< 0.05), and the MDA level was lower than in group C (p< 0.05). Moreover, alpha diversity in the gut microbiota of calves in group B was higher than that in group A and group C (p< 0.05); the dominant phyla wereFirmicutesandBacteroidota, whereas the dominant genera wereUnclassified-LachnospiraceaeandRuminococcus. Linear discriminant analysis showed that the relative abundance ofBacteroidesin the gut microbiota of calves in group B was higher than that in group A, and the relative abundance ofPrevotellaceae-UCG-003was higher compared to that in experimental group C. Thus, dietary supplementation of 80 mg/kg of Zn amino acids to calves could improve the immune function and antioxidant capacity, as well as enrich and regulate the equilibrium of gut microbiota, thus promoting the healthy growth of calves.