Effects of Organic Zinc Supplementation on Gut Microbiota and Health-Related Biomarkers in Healthy Adult Dogs

Abstract Zinc is an essential trace element involved in multiple biological processes; however, despite its well-established biological functions, studies investigating the effects of organic zinc supplementation in dogs are scarce. This study evaluated the effects of organic zinc supplementation on immunological, antioxidant, metabolic parameters, and the gut microbiota of adult dogs. Ten Beagle dogs were subjected to a crossover experimental design, receiving a basal diet with or without supplementation of 150 mg/kg zinc in the form of proteinate. Blood samples were collected throughout the experimental period for hematological, biochemical, immunological, and oxidative analyses, and fecal microbiota was evaluated at the end of each period. Zinc supplementation significantly increased serum zinc concentration ( P < 0.05), confirming its greater bioavailability. A higher total leukocyte and lymphocyte count was observed on day 44 in the supplemented dogs ( P < 0.05), without alterations in erythrocyte or platelet parameters. In the immunological profile, the supplemented dogs showed higher serum concentrations of IgG, IL-2, and IFN-γ, as well as greater adenosine deaminase and cholinesterase activity ( P ≤ 0.05), whereas no differences were observed for IgA, C-reactive protein, or ferritin. In metabolism, zinc supplementation significantly reduced serum concentrations of total cholesterol ( P < 0.05), with no effect on glucose or albumin. Regarding oxidative status, the supplemented dogs showed increased superoxide dismutase activity ( P < 0.05), with no changes in reactive oxygen species or lipid peroxidation, suggesting an enhancement of antioxidant defense rather than oxidative stress. Zinc supplementation did not disrupt gut microbial diversity but was associated with selective shifts in the relative abundance and predicted functions of specific bacterial taxa, despite pronounced inter-individual variability among dogs. It is concluded that supplementation with organic zinc promotes positive adjustments in the immune response and antioxidant system of healthy adult dogs, without compromising oxidative homeostasis or the overall diversity of the intestinal microbiota.